Thanks so much, Mark. I would consider doing this, but Netflix has offered me a lot of money to limit my video production so they can stay in business :)
WOW!!!! THANKS AGAIN!!! Why did they not teach us this stuff in school!? They should have a salvaging & fixing broken things instead of chasing paper & disposing of old things. I did learn how to sit at a desk & push a pencil to sleep![;?
When I am given an old piece such as this one to 'service' / modify, as a matter of course, I replace all original capacitors (for what they worth...). Also, some of the high power resistors in the power supply may have run out of spec due to heat, so it is wise to replace those also. In doing so, you give the amp a new lease of life for many years. Thanks for the video, great narration!
This should definitely be taught in school. I currently have a 70s AC30 open, that had the reverb and tremolo ripped out and the tube heating converted to extra smoothed DC. I managed to trace it (I understood the phase inverter thanks to your video) and am now trying to diagnose the hum and crackle. It still has original can caps in there. It works, though. Nice hobby - I'm in IT for money, and a point-to-point wired amp is something different from what I usually get to see. Anyway, I measured the DC voltage on those cans, but I didn't think to measure the ohms. Will do that now. Glad I shelled out for a nice Fluke meter. Thanks for your videos!
It's amazing...the entire 4 sections were kaput. Usually only one or two sections are bad. This cap was practically shorted. I recently repaired a '69 Fender champ with a filer cap that was as bad as this one. what was even worse was, as soon as you turned it on, and before the tubes could warm up, the 120 cycle hum was right there instantly. Yours was really bad though. It's not often you get one that hums like that one :) Gotta admit, Rusty's cap sniffing abilities are amazing :)
This is definitely the worst one I've seen in a long, long while. A dead shorted cap will usually blow a fuse or fully illuminate a current limiter bulb, but the partially shorted ones will blast you with that dreaded 120Hz tone. I wanted all the beginners to hear that sound, so they will be able to recognize it quickly and know what it indicates. Rusty is still sneezing after smelling that wretched cap.
Hi Uncle Doug & Rusty, I hope your all well. Nice little amp. Learning all the time, Thankyou for all the Time & Effort you and Rusty put in making videos and Teaching. Always looking for a new Uncle Doug & Rusty video, old one's are great. Summer is Waning. Have Fun, be good, C.
Once I had a cap blow up a giant wound resistor and trip the breaker at my house at once. Granted, it was the mains filter across the power cord. The worst thing about it is that it was actually the new replacement I had put in.
Overall an informative video. In most vintage Tube amps, or Tube amps older than 30 years .. it's a good idea to just replace all electrolytic capacitors by default ... it'll reduce the chance of ending up with input & output transformer "burnouts", and saves Tubes / Valves too ( as fuses often fail to react to such faults, as the faulty components can act as a "Hot running" resistor) Just a quick one: When measuring any components ... make sure they're not connected in any circuit ... as you're just going to get a false reading due to the other components connected to it etc. So, always disconnect at least one "leg" of a suspicious component, so it's disconnected from the rest of the circuit. ( semiconductors, such as Tubes / Valves and transistors need often be removed and tested separate, in designated Tube /Valve testers.... or in the case of transistors, in modern digital component testers etc.).
Thanks again for another excellent video, Uncle Doug. I have a 1954 Bogen Challenger 33 that a gracious Craigslist seller gifted to me. It had terrible filter caps. In fact, it wouldn't even turn on without blowing the fuse. An amp tech friend of mine helped me to replace all of the electrolytic caps, including the terrible paper and wax caps. Well, the amp sounds fantastic now. I wanted to keep the amp as original as possible, so I bought some old style mic connectors from Mouser and grafted them to the ends of guitar cables. I love the unique sound of this amp, and do not plan on changing any other part of the circuit.
You're welcome, RW. It sounds like a great amp that has found an appreciative home. I like the fact that you are keeping it original, down to the microphone connectors. Keep up the good work.....and best of luck with all your projects.
Awesome video, I don't get the chance to work on much tube equipment these days, but I really enjoy studying theory and repairs in your videos. I don't know if you ever serviced a lot of tvs in your time, but I'd have to say the worst capacitors I've ever seen were in mitsubishi/electrohome tvs. Every single electrolytic was defective and would leak, causing corrosion and damage to the boards and create any imaginable problem. They were decent sets otherwise. I really enjoyed working on them. When I had time, I would troubleshoot each problem one by one, instead of just replacing the capacitors without doing any tests. It was often a smelly job, smelled like fish or boiling nut oils far beyond normal temperatures. Many would just go visibly open.
Thanks, T1. I repaired several Philco Predicta TV's many years ago, but have since hidden/declined whenever anyone asked about TV repair. It is true that some caps were doomed to fail shortly after manufacture, while others seem to last forever.
Dude... I'm mostly just a mere vulgar musician and I understand about 30% of the technical stuff you go into but I've been following pretty much all your videos and I gotta tell you : you're one of the most entertaining people on « youtube-land »... Keep it up! Next time though ; just skip right to your good old Rusty-meter to troubleshoot these things ; it'll save you the hassle! ;)
Thanks, Adrien. You're right about it being simpler to go straight to trusty Rusty.....but his contract requires that I at least try some other methods first, so as not to unfairly interrupt his nap time :)
You have new subscribers all the time, so more great info for troubleshooting tube amp problems. You had plenty of room to replace the 4 section filter cap with singles. A lot less money too! Rusty continues to be your go to troubleshooter.Thankz
You're welcome, Mega. Every once in a while we just like to have some fun, and these ridiculous filter caps were a good excuse to do so. We're glad you enjoy the videos :)
Its a nice video, thank you! I don't think I would trust those old carbon resistors too far. While its nice to keep things original, reliability becomes an issue particularly if its going to be pushed pretty hard. I used to work on jukebox amps quite a bit. They took quite a beating. I can only imagine what the guitar people will do to this amp! :)
I do new builds with carbon comp resistors. There is nothing wrong with them and when chosen for select places like plate loads their high voltage coefficients will add some nice nonlinear distortion to the signal. This is of course wanted in guitar amps so be careful when replacing CC resistors, you may just make the amp too sterile by switching to film resistors. The larger the signal swing across the resistor the more harmonic distortion will be added. To those that say they are "noisy", ones that have failed can sound like bacon frying in a pan but high quality CC resistors will not make your amp noisy. The last high gain amp I made had an output noise level of
Hey Doug and Dog, I found your channel through a link on reddit a few days ago, and have been binge watching since then. I just wanted to say thanks for taking the time to make these videos - you have inspired me to no end! I am currently filling a basket on rs online (UK radio shack equivalent) with some tools to get started on my own. I recently bought my first proper electric guitar set up (classical guitarist of 10+ years) and am in dire need of a tremolo effect, so I am gonna start with the mechanical tremolo you posted a while back. I'll post a reply on that video when I am finished!! Thanks again Doug and Rusty, Tom
You're welcome, Tom. We're really glad that you found our channel. The mechanical tremolo requires a lot of lathework and machining. Have you seen the Ricktone tremolo videos? It's purely electronic and might suit your needs better.
Rusty's skills are beyond question. Dated parlance translated--"Rusty sports the mad skills"...very 90's but I'm not as cool as I once thought I was. P.S. I'm pretty sure (based on what I've seen/heard thus far in the Uncle D. videos) that the capacitors in my newly acquired Carvin amplifier will need to be replaced. I'm going to watch/learn for a few weeks before taking any action...I'm in no hurry to be wrong AGAIN so i'll keep consuming the 'course material' indefinitely. Thanks again guys!
Hello Uncle Doug and and company! I'm happy to report that I simply had to replace a couple of pre-amp tubes to solve my problem after determining that it was merely 60hz hum that needed to be remedied. I think after a full re-tube and a tuning of the bias will make my Carvin MTS combo the amp it can be which should be ultra low noise, good clean channel with plenty of nice tube warmth...just gonna start with a simple matched set of EL34s, maybe try a low noise 12ax7 in V1 and regular JJ's in v2-5. Think that will make the mild,but present 60hz hum altogether disappear. Also Uncle Doug, I'd love for you to see this UNCLE Alberts Del Ray--very neat amp and would love to show ya--just go to Craigslist Indianapolis and search musical instruments and enter tube amps...won't be long before you find this intriquing and gorgeous piece of masterwork. It is really really neat! Peace out Dawg(as they said in the 'hood before it became trite.)
Hi Uncle Doug. I have a question. I restored a 1940 Zenith radio console around 2012and used a variac at 110v during operation. About a month ago, I heard several "pops" (about 15 min apart). As the radio died on me I heard a sizzling sound from the speaker. The transformer, because I had used a variac, was warm to the touch didn't smoke on me. All the tubes checked okay. I have to remove the chassis from the cabinet power and check the power circut. If the transformer did go bad on me, what advise can you give me to have the console paying again? Thanks
Long distance radio repair is simply a guessing game, Jorge. A variac will not protect the components in your circuit. For protection, you need a current limiter (see my video). You will have to test the primary input and all the secondary output windings of the power transformer with an ohmmeter (for continuity). If it fried, then you'll have to track down and install an suitable replacement. Good luck.
What model? There was one or two Zeniths around that era that used a pair of 6X5Gs for rectifiers. It was an improper design, and they paired them up with a marginal power transformer for the size of the radio, so they were notorious for shorting and burning out the H.V winding. There are two ways to check the transformer, one is by taking resistance measurements, the other is by pulling the tubes out and powering it up. A failed power transformer usually has one or more shorted windings and will get red hot within minutes, which you can also find by measuring the resistances of each winding, particularly the H.V winding between each outside leg and the center tap. It's possible that the sizzling was a tone correction cap across the output transformer primary, that cap has to be a high voltage one or it can fail and short out.
Whenever I see that type of cap on my radios, it's automatically replaced! LOL! Glad you left the structure above the chassis! That's what I do, wire the new caps under the chassis! Rusty is on point...as per usual!
Uncle Doug, I would sure love those old caps, the stripped once’s especially... Great artwork just waiting to be displayed if you wanted to help with that... Ms. gulf coast
Uncle Doug would be awesome if you did. I’m sure I could round you up something that could help with a video... I got an ex wife whose as annoying as a Sub tweeter, wish somebody would tune her up.. lol thanks uncle Doug, great video as always
Hey Uncle Doug, I'm a couple of years late to the party, but seriously surprised not to see one comment about the Kinks riff. Please include more Kinks riffs in your guitar-amp testing repertoire. Keep it up!
Another really fine video on troubleshooting. From a safety point, all rings, bracelets and dangling metal jewelry should be taken off (2:05) when working on these high voltage circuits. I also assume the filter cap was discharged before measuring the ESR. Thanks!
We agree, TM, and yes, as discussed in many of our videos, all filter caps are discharged prior to any work on the chassis, especially when taking ESR measurements.
Hi Uncle Doug, I've recently been thinking of buying an ESR Meter, then I figured you can buy a lot of new filter caps for the same price and old caps aren't something that improve with age like a fine wine! Also, I just completed a Ricktone Tremo-verb, ironed out the faults, and was inspired to make a SE amp I used the back to back transformer design to make a Champ clone with a 6aq5 in the power stage, works great. Kind regards to you and your four legged friends, Colin.
I understand the economics of ESR vs simply buying caps, Colin, but in the long run....especially if you do this a lot.....it will pay off (I think :) Congratulations on your successful Tremotone and Champ projects. It's great to hear that the videos are helpful.
Hey Uncle Doug ! Well that was a loud noise ! I always enjoy watching your videos I've learned( and still learning ) a lot !! Thank Yoiu for sharing your knowledge ! Have a great day ! and give my best to Rusty and Jack
I notice that you add plastic insulation over the leads of some of your electrolytic capacitors (but not all of them). Why is this done and when should it be done? Many thanks again for taking the time to teach us.
I sure miss working on vacuum tube stuff, I am slowly getting back into it but on a very small scale due to space & money. Those 6L6 tube amps can sure punch out the power. I just found your channel, good video Uncle Doug
Great vid. Were they vintage bumble bee caps you pulled out? If they match your new replacement ones and they are not leaking you should use them. Mojo! I'm in the process of putting them in my les Paul along with 50's centralab harness and belden wire with a pair of t tops.
Yes, they were, Tock.....and I intend to test them and add them to my vintage parts stash ASAP :) Regardless of their tone capabilities, they really look neat in a circuit.
Burstein-Applebee PA amp? I was a part counter kid at one store in the mid '70's but I don't remember seeing anything like this. Thanks Uncle Doug and Rusty.
Nice job on getting rid of the 120hz hum. I wish I could understand electronic circuits. I have a pair of 1959 Stromberg Carlson 6550 push/pull mono block tube amplifiers that are actually NOS never been used in original boxes. I can’t find a technician in New York State that can go through them I have really very little education in regards to electronics. Sure wish I could find a technician to test this so I may use them as home audio mono blocks.
Rusty sneezing. yes That can was shot. I've seen 2 4 section caps with all 4 sections read less than 200ohms .They both were scorched and someone had put a 20 amp fuse in place of a 3a. very lucky the transformer was still ok!!!! Thanks for your videos. They help me in areas im short in
Complete noob here. When you are using the multimeter [on Ohms] I can see the positive test lead but where is the the common lead? Don't you need both to complete a circuit for a proper read? Please let me know. Thank you kindly
HEY! Do you do this for a living? Because I got a record player that has a really bad hum and I know it’s the capacitor, but only if you live in Texas, because that’s where I live
@@UncleDoug aww man, that’s too bad, because this thing hums worse than that radio you showed, and it makes the music that comes from the vinals sound terrible
this comment is made prior to that can capacitor, caps like that are the main reason prior to such loud hums, because the electrolytic fluid in that capacitor is no more, there is hum as a result of it's high resistance, usually the resistance in the can electrolytics are low and able to be used as long as they are neither leaky or dry because it helps keeping the tubes inside(if any) from red plating
Excellent demonstration of the Rusty test! Very nice raunchy sound, is the bias set cold? Was Jack on camera for this one or relaxing on the couch. :))
Thanks, Andrew. The PD was 16.5W for metal 6L6's.....which is just about optimum in my book. I think the guitar input was overdriving the octal pre-amp, but the moment I heard the resulting tone, the Kinks came to mind :) Jack is on hiatus for a couple weeks, studying astrophysics at MIT.
Uncle Doug Right you are! You guys have a great night! Thank you for the great videos. I am an industrial electrician/maint tech but limited in electronics. With a few good tube amp books and your truly great videos I am gaining more and more knowledge about my beloved tube amps. Thank you very much for sharing your wisdom and knowledge!
Hi Uncle Doug - thanks for all the great videos - I don't even have a tube amp but I still enjoy them ! Did you have to train Rusty to be a component sniffer ? Or is it one of those things some dogs are just born with ? My dog demonstrates no obvious diagnostic skills. Maybe I could start her out with some dog-bone resistors and work up from there ?
You're welcome, Christopher. Rusty was just a natural-born component sniffer. Even as a pup, he would sniff and bark at faulty transformers and electrolytic caps. Jack, on the other hand, is slowly developing his cat scanning abilities, but he's still young and I'm optimistic about his future in diagnostics. Perhaps your dog would be more interested in circuitry if you started using bacon as shrink-wrap :)
My electronics teacher showed that a new electrolytic cap will have a low resistance until it charges to the meter's output voltage. However, that 120Hz hum says bad caps in billboard-sized lettering. Loud distortion at 2 means high input level. Guitars put out 0.5v, microphones, about 0.05. Possibly a second input for a clean signal is needed? It's what I'd do, anyway.
If you watch any of my more recent videos, I make a point of doing this......but more importantly, on this channel, we don't begin our comments or responses with insults, like "Dopey". If you wish to participate in correspondence, then please heed this rule.
Hey Mr Doug build some more amps please sir LOL. I'm electronically zero'd but you and another guy, Tony McKenzie, on YT inspired me to try so I ordered a MOD 102+ kit complete with very explicit instructions (Very). I took my time and was quite successful. I've been building speakers for years so I ordered a british celestion GH12 or some such and boxed it. I'm really impressed with myself. It sounds better than either my fender or my marshall. LOL. Thanks Doug.
they do get bad over time...they simply dry out. and while they do so the aluminium foil which forms the capacitor may come so close that they eventually shorting out if you apply any voltage on the terminals. Or the electrolytic which forms the insulation between the foils become some kind of plastic and makes that very thin foil cracked and then there is no capacitor no more just two terminals connected to nothing....
I observed one electrolytic cap go in a mac 2120. Like a mini volcano. Very cool. It had a very peculiar smell. Is that smell always the same when they go or when they are thinking about it? I've noticed that smell on some other vintage gear.
Since you're talking about caps.. Doug, I've ordered a HI-Fi tube amp kit and on the power supply circuit the schematic says I need a 150uF/450V Electrolytic cap just after the choke.. Question is, can I stick in there a 470uF/450V cap, providing it fits, or is that overkill and/or detrimental? How about a 500V or 600V cap at 1000uF? LOL. Guess what I'm asking is..can I install the biggest cap I want? Back in the 90's I scratch-built a 12V brick-style power supply using the biggest transformer and caps for the voltage regulator I could buy for a secondhand car amp I used to drive my scratch-built speakers which sounded good and loud in my room and hadn't any trace of hum/buzz. I'm not a total noob to electronics but electron tubes/valves are new territory and I'm finding them so fascinating! I'm loving the idea that, once completed, my amp won't have a single semiconductor within it and will be as far removed from digital as possible, apart from the on-off switch! Loving your videos even though they center on guitar amps mostly but the principal is the same and I'm soaking them up.
The simple answer is no, Dennis, you can't arbitrarily increase the values of capacitors in a power supply. Engineers dictated the proper values and their choices should be followed. A slight increase, i.e. 22uf instead of 20uf, is OK, but you risk damage to your rectifier tube (and gain nothing) if you greatly increase filter capacitance.
This is what you found in old amps....the other day i found some light bulbs wired in as cathode resistors for the output tubes in a *fixed negative grid biassed* amp....if you push that amp very hard they do light up and add some resistance in this path and save the output tubes from dissipating too much power.....
I believe the Hammond AO-44 (or perhaps the AO-39) uses some light bulbs as variable ballast resistors. It's actually a very clever solution, probably developed before varistors appeared on the scene.
Hi Uncle Doug, stupid question time... I noticed in a few cases now that you have chosen to replace cans with axial electrolytic caps. Is it based on availability or is there another reason? I recently replaced all the cans on a Hiwatt DR-103 and used all new cans that were readily available to me. Just curious. As always, great video! Give Rusty a scratch for me.
This was a customer amp, JC, and cost was a definite consideration. The separate caps were much cheaper than a replacement can.....and I had the individual caps on hand, while ordering a replacement can (if one could be found with the proper values) would take several days. If this was a Blackface Fender Deluxe Reverb I was restoring to keep, I would order and install the proper can caps.
+Uncle Doug : completely understand and it makes sense. I have had experiences where I could not the original parts and used what was available and everything was just fine. Project economics drive many considerations. Speaking of considerations, excellent job in your recent capacitor series installment explains the differences, why's, and applications for various capacitors. All the best!
With my small video camera microphone I have to be careful not to overdrive it too much, or the resulting distortion will give a false impression of the amplifiers true tone. The "2" was indeed rather loud :)
If you don't mind me asking what area are you in? I'm in long beach, ca and so hard to find good techs that know much about this stuff. I had a great one for years...Red Rhodes...also a great steel pedal guy ( sweet baby James) but he's gone now unfortunately. I collect many old fender amps but always in need of repair. Thanks and for your videos! Hi to Rusty!
Rusty and I are in West Texas, David, about 850 miles east of you. We're very flattered that you would seek our help, but we've retired from doing outside work. Hopefully, you can find another trustworthy tech in your area. Best of luck.
looking at your videos, i don't see a lot of star grounding in the amps. how common is it? and in your opinion, how important is it? I've only built a handful of tubeamps, but i've always stargrounded. having caps connected to separate points on the chassis will make currents run in the chassis itself, possibly leading to noise, no? am I wasting my time stargrounding?
I can't say that you're wasting your time, Borgar. Many very knowledgeable people swear the star grounding is the only way to go. In my own experience, using both star grounding and (good, logical) multiple-site grounding, I don't really hear much difference. My recent Supro build (see the video series) uses what I call "common sense" grounding (not star) and it is dead silent. Yes, there may be tiny differences in potential within the chassis, but they are primarily DC......which is silent.
I know, it's not that I'm going to use the amp without the guitar plugged in, I was just worried as to why it was doing that..it's kind of strange.the thing that's really bothering me is the short duration of crackles and pops at startup .im worried to use the amp because I heard of the caps are bad causing that then the power supply can be damaged if I use the amp with bad caps?
The primary indicator of failing filter capacitors is a 120Hz hum (i.e. double AC supply frequency). If you are truly concerned about the noises, then take the amp to a qualified technician and have them check it out.
Hey there Doug! great videos! I love them. I was wondering if there are like a couple of precautionary steps (in summary) for working with high voltage amplifiers? I know that one must drain all the capacitors by using a resistor and shorting but besides that is there any other dangers lurking around? I have had questions like if you touch a transformer (like those big ones outside some amplifiers) can you die? should you cover them all the time? Ive been wanting to tinker with tube amps but im afraid I do not have the sufficient knowledge for that. Thanks again for the great and informative videos
Safety precautions, including how to make your own capacitor-draining tool, are included throughout the videos, 39P. You really need to watch and acquaint yourself with all of them before touching any of the wiring or internal components of a circuit. A couple of quick suggestions: Never be grounded (skin touching concrete, pipes, etc.), and never touch any circuit with both hands (keep one in your pocket).
Their circuitry is extremely elaborate, they are difficult to re-calibrate, and they are easily damaged by shipment and rough handling. I would suggest a Hickok tester, from a seller with flawless feedback who will accept a return, if necessary. Good luck.
You would think so, but the Current Limiter bulb did not illuminate. The capacitor can got real hot, however, so there is definitely some current flowing through the leaky caps (which had become resistors) to ground.
I heard a noise like that just before that amp I told you about caught on fire...It was just a little fire that went out within seconds... I big ceramic resister blew up and a couple of others looked cooked. I'm learnin the hard way but i don't mind...thanks again for these videos. ..and rusty was right bout those can capacitors they stink!
Yes indeed, if you don't pull the plug quickly on a roaring hum like the one in the video, something is either going to catch fire or explode.....and you can't believe the mess an exploding electrolytic capacitor can make :( Keep on learning, YR. Often learning the hard way makes the longest-lasting impression.
Hi Uncle Doug! I love the videos you are posting. I know you have said you get your parts at antique supply and power supplies at another site. I haven't had any luck finding an old mallory capacitor (500V/30 MFD, 500/10, 450/10, 450/10) that would help me fix a 4 channel Rauland 2135 pa amp. Is there somewhere else you go to find anything along this order? Sorry if you answered this question in another video, i am still working my way through them.
It's often impossible to find the exact can cap you need, Erik, which is why I generally resort to installing individual axial caps within the chassis, leaving the old can in place for looks. I know of no other good sources for the can-style capacitors.
Thank you for your response. Finding the original would be a one in a million at this point lol. After more hunting and calling several manufactures. The problem is finding a replacement cap 500v/30. I was able to find a 450/30 and a 600/30 and 450/10 for the others. I am not sure what one to go with. Does the voltage rating affect the tone or have any ill effects on the transformers? If a surge pass thought the cap at 600v that would normally fail with the original, would i be doing more damage than good using a 600v cap? Maybe add a 500 v fuse to protect the rest of the amp? Any thoughts on what to do when you can't find the right volt value capacitor are appreciated. Thank you for your time.
Looking in the circuit with another few years research in my brain, I see Tiny Chief caps... those are paper/oil type, and like Bumblebees do go bad with age... did those get tested too?
Cool deal. I'm re-capping a 1979 Peavey Mixer... it had 120hz whine.. and since it's been an on-the-road concert mixer, it's seen and heard a great deal. There's only 350 or so Electrolytic caps. Some are bulged, some leaked, all are getting changed... Fun Fun Fun... Tedious as heck.
Got it all done (350+ caps) ... it's a long boring video. However, I recorded my DIY leslie speaker in Stereo, and that worked great. My DIY leslie is a little different than yours... but not too much. we started with the same drum... I had a 10" speaker, and a relay to use as a foot switch on/off. All that stuff is posted.
Doug, got a question. I'm starting to do my own amp work. My first project is replacing the filters on my Marshall JCM 800 50W amp, and biasing new power tubes after the cap job. I have a tube bias adapter, so good there, but the filters came with two smaller caps, and I wanted to check to see if those, still on the board are in spec. Can these be checked in circuit with a multimeter? Or do they have to pulled from the board and tested, or can an in-circuit ESR meter tell me what I need to know? If the proper way is with an ESR meter, any suggestions on one that will work for amp repair or maintanance? I am looking at a few for sale, but need to make sure I'm looking at ESR's that can do amp work ranges...I just want to be able to check if they are in spec within tolerance. Thanks!!!
You really can't fully test capacitors with a multi-meter. Even if the capacitance reading seems appropriate, the capacitor could still be faulty. ESR meters are specific for electrolytic caps and much better at spotting failing ones, but they don't fully charge the cap to operating voltage, which is about the only absolute way to judge them. I have an Anatek Blue ESR meter and use it all the time. It may not be the absolute most-thorough method to sniff out failing electrolytics, but it very practical and effective. You can use an ESR meter to measure all electrolytics in circuit, unless they are in parallel.....which is quite rare.
Thanks for the reply. So I would be able to test electrolytic caps in circuit with a decent ESR meter? I was looking at either the Anatek Blue or the Signstek MESR V2. I was just looking for a way to test electrolytics to see if they need replacing while still in circuit on my vintage amps. De-soldering would not be a big deal, but was wondering if it can be done reliably enough in circuit with either a multimeter, or a decent ESR meter. I'm going to be looking at as many videos as I can to see how testing on caps in amps like mine are done to determine whether or not they need replacing. I see you have a vid on this with the Blue, so I'll be posting there. Like I said, replacing the filters is straight forward enough, and re-biasing the JCM 800 out put tubes looks easy enough, but diagnosing the electrolytics has me baffled right now. I believe my Hiwatts and Sound City amps on the other hand, ( correct me if I'm wrong please..) dont have bias pots and will need to adjust bias through the resistors. Thats for another time. Right now the JCM is the easiest platform to start with. Thanks for the replies Doug!!!
It’s like if Steve Martin fixed guitar amps! Uncle Doug is hilarious great videos too very informative. Tell cousin Jack congratulations on being an astrophysicist! And I think Rusty’s only pretending to sniff the bad caps out y’all... he can probably only tell due to his esp
Hi Douglas, Was that four electrolytic smoothing capacitor canister, incorporated into the PE30 amplifier, manufactured by Hunts Capacitors of London (now mercifully no longer in business)? I ask this as Hunts capacitors had a reputation for being unreliable. I always evict the blighters whenever I see them beneath a vintage radio’s chassis. What is that ESR meter you use? I’m curious! 73 de Phil.
I'm not sure, Phil. The only unusual characteristic was that it was abnormally tall.....about 6". The amp was picked up by the owner yesterday so I can't check it. I use an Anatek Blue ESR meter. They have a great website, excellent service, and great products.
That's a good question, Jozef. I ran every test but that one. The amp is gone now, so it's too late to check, but I would imagine their capacitance to be quite low....if any.
Hey Doug, thanks for the videos 😃I have a question regarding a SS amp. I have a Marshall MG 15. The Neutral prong on my plug broke off and it heated up pretty good. I noticed the wiring coming out of the transformer got a little cooked. After going through a couple of fuses, i fixed the plug, but now I seem to be getting a lot of "what i thought " 60 cycle hum. A person i was talking to said i probably burnt out a filter. Was he talking about a filter capacitor? Do SS amps even have filter capacitors? Im wondering if what i hear is actually 120 cycle hum... great channel by the way. I am learning a lot about how to work on my Fender Hotrod Deville (my "real" amp) through your channel.
There is no telling what harm might have been done by overheating, Kyle. Yes, SS amp power supplies use filter capacitors. You might want to get a qualified tech to look it over.
Uncle Doug thanks for the reply. Around my area work is expensive, and questionable at best. Id be better off just to get a new amp, ill just have to do some more research. Got alot to learn :)
Interesting to note that the can cap showed no signs of failure. Bubbling of electrolytic etc. unfortunately I have cats and they only want to crawl inside amps and do nothing to help me in amp diagnostics. All hail Rusty!
What were all of the capacitors that you removed from the amp to bring it back to "as designed"? Was that someone else's attempt to bypass the stock filter capacitor? Oh, and Hey Rusty, what's up?
![[#2024MAMA] ROSÉ (로제), Bruno Mars - APT. | Mnet 241122 방송](http://i.ytimg.com/vi/dgGqD28J6aQ/mqdefault.jpg)
Uncle Doug, if you would just produce 1 video a day I would cancel my Netflix account. Really enjoy and learn a lot.
Thanks so much, Mark. I would consider doing this, but Netflix has offered me a lot of money to limit my video production so they can stay in business :)
@@UncleDoug Sell out....you're the man Doug, and Rusty of course.
@@donaldlogan3626 Thanks so much, Donald.
@@UncleDoug Personally ... I think you're all wired up ... heh-heh.
@@Tonetwisters My wife would agree, TT.
WOW!!!! THANKS AGAIN!!! Why did they not teach us this stuff in school!? They should have a salvaging & fixing broken things instead of chasing paper & disposing of old things. I did learn how to sit at a desk & push a pencil to sleep![;?
You're welcome, Wyatt. I agree that practical, hand-on training is way better than boring lectures and theory. Thanks for watching and commenting :)
Because school won`t teach you anything you need in real life after the first 3-5 years ;)
When I am given an old piece such as this one to 'service' / modify, as a matter of course, I replace all original capacitors (for what they worth...). Also, some of the high power resistors in the power supply may have run out of spec due to heat, so it is wise to replace those also. In doing so, you give the amp a new lease of life for many years.
Thanks for the video, great narration!
You're welcome, Lep :)
Dear Old Rusty, he adds SO much fun to your extraordinarily educational videos. Thanks Uncle Doug.
You're welcome, Stony. Amen :)
This should definitely be taught in school. I currently have a 70s AC30 open, that had the reverb and tremolo ripped out and the tube heating converted to extra smoothed DC. I managed to trace it (I understood the phase inverter thanks to your video) and am now trying to diagnose the hum and crackle. It still has original can caps in there. It works, though. Nice hobby - I'm in IT for money, and a point-to-point wired amp is something different from what I usually get to see. Anyway, I measured the DC voltage on those cans, but I didn't think to measure the ohms. Will do that now. Glad I shelled out for a nice Fluke meter. Thanks for your videos!
You're welcome, KD. Best of luck with your projects.
The 196 ohm reading was measuring the Output Tube cathode bias resistor...
Good point, AK. Thanks for spotting it :)
You continually restore my faith in humanity, thanks Uncle Doug!
You're welcome, Nf. That is our mission in life :)
It's amazing...the entire 4 sections were kaput. Usually only one or two sections are bad. This cap was practically shorted. I recently repaired a '69 Fender champ with a filer cap that was as bad as this one. what was even worse was, as soon as you turned it on, and before the tubes could warm up, the 120 cycle hum was right there instantly. Yours was really bad though. It's not often you get one that hums like that one :) Gotta admit, Rusty's cap sniffing abilities are amazing :)
This is definitely the worst one I've seen in a long, long while. A dead shorted cap will usually blow a fuse or fully illuminate a current limiter bulb, but the partially shorted ones will blast you with that dreaded 120Hz tone. I wanted all the beginners to hear that sound, so they will be able to recognize it quickly and know what it indicates. Rusty is still sneezing after smelling that wretched cap.
Great troubleshooting! I always learn something when I watch one of your videos.
Hi Uncle Doug & Rusty, I hope your all well. Nice little amp. Learning all the time, Thankyou for all the Time & Effort you and Rusty put in making videos and Teaching. Always looking for a new Uncle Doug & Rusty video, old one's are great. Summer is Waning. Have Fun, be good, C.
We will, Cass. You're welcome. It's always good to hear from you :)
Once I had a cap blow up a giant wound resistor and trip the breaker at my house at once. Granted, it was the mains filter across the power cord. The worst thing about it is that it was actually the new replacement I had put in.
Wow, that would be a bad combination....an explosion that involves a newly purchased part, and it all happens in the dark :(
Solder in backwards ?
Overall an informative video. In most vintage Tube amps, or Tube amps older than 30 years .. it's a good idea to just replace all electrolytic capacitors by default ... it'll reduce the chance of ending up with input & output transformer "burnouts", and saves Tubes / Valves too ( as fuses often fail to react to such faults, as the faulty components can act as a "Hot running" resistor) Just a quick one: When measuring any components ... make sure they're not connected in any circuit ... as you're just going to get a false reading due to the other components connected to it etc. So, always disconnect at least one "leg" of a suspicious component, so it's disconnected from the rest of the circuit. ( semiconductors, such as Tubes / Valves and transistors need often be removed and tested separate, in designated Tube /Valve testers.... or in the case of transistors, in modern digital component testers etc.).
Thanks for your helpful input, Robert.
Thanks again for another excellent video, Uncle Doug. I have a 1954 Bogen Challenger 33 that a gracious Craigslist seller gifted to me. It had terrible filter caps. In fact, it wouldn't even turn on without blowing the fuse. An amp tech friend of mine helped me to replace all of the electrolytic caps, including the terrible paper and wax caps. Well, the amp sounds fantastic now. I wanted to keep the amp as original as possible, so I bought some old style mic connectors from Mouser and grafted them to the ends of guitar cables. I love the unique sound of this amp, and do not plan on changing any other part of the circuit.
You're welcome, RW. It sounds like a great amp that has found an appreciative home. I like the fact that you are keeping it original, down to the microphone connectors. Keep up the good work.....and best of luck with all your projects.
I could watch these videos All Day And All Of The Night!
Pretty Kinky, Hijme ;)
Kudos for that short demo.
I have worked on a lot of Precision, Grommes, and Sound Craftsman amps and loved all of those oldies but goodies!
Thanks, Dennis :)
Awesome video, I don't get the chance to work on much tube equipment these days, but I really enjoy studying theory and repairs in your videos. I don't know if you ever serviced a lot of tvs in your time, but I'd have to say the worst capacitors I've ever seen were in mitsubishi/electrohome tvs. Every single electrolytic was defective and would leak, causing corrosion and damage to the boards and create any imaginable problem. They were decent sets otherwise. I really enjoyed working on them. When I had time, I would troubleshoot each problem one by one, instead of just replacing the capacitors without doing any tests. It was often a smelly job, smelled like fish or boiling nut oils far beyond normal temperatures. Many would just go visibly open.
Thanks, T1. I repaired several Philco Predicta TV's many years ago, but have since hidden/declined whenever anyone asked about TV repair. It is true that some caps were doomed to fail shortly after manufacture, while others seem to last forever.
Dude... I'm mostly just a mere vulgar musician and I understand about 30% of the technical stuff you go into but I've been following pretty much all your videos and I gotta tell you : you're one of the most entertaining people on « youtube-land »... Keep it up!
Next time though ; just skip right to your good old Rusty-meter to troubleshoot these things ; it'll save you the hassle! ;)
Thanks, Adrien. You're right about it being simpler to go straight to trusty Rusty.....but his contract requires that I at least try some other methods first, so as not to unfairly interrupt his nap time :)
You have new subscribers all the time, so more great info for troubleshooting tube amp problems. You had plenty of room to replace the 4 section filter cap with singles. A lot less money too! Rusty continues to be your go to troubleshooter.Thankz
You're welcome, ATL. As I said, it isn't rocket science, but it was SO BAD that I thought you all would get a kick out of it :)
Your videos are always the highlight of my day. It's so much fun to learn about this stuff. Thanks.
You're welcome, Mega. Every once in a while we just like to have some fun, and these ridiculous filter caps were a good excuse to do so. We're glad you enjoy the videos :)
I am still finding these gems. Another great Vid Uncle Doug! I am glad you tell it like it is 🙂
Glad you enjoyed it, Richard.
Its a nice video, thank you! I don't think I would trust those old carbon resistors too far. While its nice to keep things original, reliability becomes an issue particularly if its going to be pushed pretty hard. I used to work on jukebox amps quite a bit. They took quite a beating. I can only imagine what the guitar people will do to this amp! :)
You're welcome, Stuart. Yes, there must be a balance between originality and reliability. Thanks for your input.
I do new builds with carbon comp resistors. There is nothing wrong with them and when chosen for select places like plate loads their high voltage coefficients will add some nice nonlinear distortion to the signal. This is of course wanted in guitar amps so be careful when replacing CC resistors, you may just make the amp too sterile by switching to film resistors. The larger the signal swing across the resistor the more harmonic distortion will be added. To those that say they are "noisy", ones that have failed can sound like bacon frying in a pan but high quality CC resistors will not make your amp noisy. The last high gain amp I made had an output noise level of
A simple but important lesson! Thanks Uncle Doug and Rusty!
You're welcome, Brian. Sometimes the simpler things are the best :)
Hey Doug and Dog,
I found your channel through a link on reddit a few days ago, and have been binge watching since then. I just wanted to say thanks for taking the time to make these videos - you have inspired me to no end! I am currently filling a basket on rs online (UK radio shack equivalent) with some tools to get started on my own. I recently bought my first proper electric guitar set up (classical guitarist of 10+ years) and am in dire need of a tremolo effect, so I am gonna start with the mechanical tremolo you posted a while back. I'll post a reply on that video when I am finished!!
Thanks again Doug and Rusty,
Tom
You're welcome, Tom. We're really glad that you found our channel. The mechanical tremolo requires a lot of lathework and machining. Have you seen the Ricktone tremolo videos? It's purely electronic and might suit your needs better.
Ah that is actually exactly what I meant! Confused as I was watching your comparison video of the two as I was typing. Cheers and take care
Good luck with your project, Tom.
Thanks for the great videos Doug, Rusty must be really upset about this, give him a pat and cookie for me.
You're welcome, Strat. After a successful sniff job like this, I always treat Rusty to a treat or two. I'll tell him that one of them came from you :)
Rusty's skills are beyond question. Dated parlance translated--"Rusty sports the mad skills"...very 90's but I'm not as cool as I once thought I was.
P.S. I'm pretty sure (based on what I've seen/heard thus far in the Uncle D. videos) that the capacitors in my newly acquired Carvin amplifier will need to be replaced. I'm going to watch/learn for a few weeks before taking any action...I'm in no hurry to be wrong AGAIN so i'll keep consuming the 'course material' indefinitely. Thanks again guys!
Thanks, WTD. Best of luck with your studies and eventual repair :)
Hello Uncle Doug and and company! I'm happy to report that I simply had to replace a couple of pre-amp tubes to solve my problem after determining that it was merely 60hz hum that needed to be remedied. I think after a full re-tube and a tuning of the bias will make my Carvin MTS combo the amp it can be which should be ultra low noise, good clean channel with plenty of nice tube warmth...just gonna start with a simple matched set of EL34s, maybe try a low noise 12ax7 in V1 and regular JJ's in v2-5. Think that will make the mild,but present 60hz hum altogether disappear. Also Uncle Doug, I'd love for you to see this UNCLE Alberts Del Ray--very neat amp and would love to show ya--just go to Craigslist Indianapolis and search musical instruments and enter tube amps...won't be long before you find this intriquing and gorgeous piece of masterwork. It is really really neat!
Peace out Dawg(as they said in the 'hood before it became trite.)
Hi Uncle Doug. I have a question. I restored a 1940 Zenith radio console around 2012and used a variac at 110v during operation. About a month ago, I heard several "pops" (about 15 min apart). As the radio died on me I heard a sizzling sound from the speaker. The transformer, because I had used a variac, was warm to the touch didn't smoke on me. All the tubes checked okay. I have to remove the chassis from the cabinet power and check the power circut. If the transformer did go bad on me, what advise can you give me to have the console paying again? Thanks
Long distance radio repair is simply a guessing game, Jorge. A variac will not protect the components in your circuit. For protection, you need a current limiter (see my video). You will have to test the primary input and all the secondary output windings of the power transformer with an ohmmeter (for continuity). If it fried, then you'll have to track down and install an suitable replacement. Good luck.
What model? There was one or two Zeniths around that era that used a pair of 6X5Gs for rectifiers. It was an improper design, and they paired them up with a marginal power transformer for the size of the radio, so they were notorious for shorting and burning out the H.V winding. There are two ways to check the transformer, one is by taking resistance measurements, the other is by pulling the tubes out and powering it up. A failed power transformer usually has one or more shorted windings and will get red hot within minutes, which you can also find by measuring the resistances of each winding, particularly the H.V winding between each outside leg and the center tap. It's possible that the sizzling was a tone correction cap across the output transformer primary, that cap has to be a high voltage one or it can fail and short out.
Whenever I see that type of cap on my radios, it's automatically replaced! LOL! Glad you left the structure above the chassis! That's what I do, wire the new caps under the chassis! Rusty is on point...as per usual!
This can cap was unusually tall, at least 6". In the future, I will be on alert for the tall ones :)
Uncle Doug, I would sure love those old caps, the stripped once’s especially...
Great artwork just waiting to be displayed if you wanted to help with that...
Ms. gulf coast
I always return the old, removed parts to the owners, 76. I'll see if I can amass some old caps for you.
Uncle Doug would be awesome if you did. I’m sure I could round you up something that could help with a video... I got an ex wife whose as annoying as a Sub tweeter, wish somebody would tune her up.. lol thanks uncle Doug, great video as always
Hey Uncle Doug, I'm a couple of years late to the party, but seriously surprised not to see one comment about the Kinks riff. Please include more Kinks riffs in your guitar-amp testing repertoire. Keep it up!
We will, Cory :)
Another really fine video on troubleshooting. From a safety point, all rings, bracelets and dangling metal jewelry should be taken off (2:05) when working on these high voltage circuits. I also assume the filter cap was discharged before measuring the ESR. Thanks!
We agree, TM, and yes, as discussed in many of our videos, all filter caps are discharged prior to any work on the chassis, especially when taking ESR measurements.
Nice video, Uncle Doug and Rusty! The nose knows!
Thanks, Bart. His diagnostic skills are truly impressive :)
Hi Uncle Doug, I've recently been thinking of buying an ESR Meter, then I figured you can buy a lot of new filter caps for the same price and old caps aren't something that improve with age like a fine wine! Also, I just completed a Ricktone Tremo-verb, ironed out the faults, and was inspired to make a SE amp I used the back to back transformer design to make a Champ clone with a 6aq5 in the power stage, works great. Kind regards to you and your four legged friends, Colin.
I understand the economics of ESR vs simply buying caps, Colin, but in the long run....especially if you do this a lot.....it will pay off (I think :) Congratulations on your successful Tremotone and Champ projects. It's great to hear that the videos are helpful.
Hey Uncle Doug !
Well that was a loud noise ! I always enjoy watching your videos I've learned( and still learning ) a lot !!
Thank Yoiu for sharing your knowledge !
Have a great day ! and give my best to Rusty and Jack
You're welcome, Brogh. Let's hope that neither of us ever hears that sound again :) Rusty and Jack say "Hi".
hehe :) I really hope we all do !!
Looking forward to the next video !!
Seriously!!! Thank you so much for all you contribute!
You're welcome, DR :)
I recognised the tune , that must give my age away, nice video Doug
Thanks, Paul :)
I notice that you add plastic insulation over the leads of some of your electrolytic capacitors (but not all of them). Why is this done and when should it be done? Many thanks again for taking the time to teach us.
It's to prevent any inadvertent contact between the wire leads, Jon, and is done where necessary.
@@UncleDoug Thanks. I wanted to be sure that it wasn't for signal shielding or something more complex.
@@TheJstewart2010 Vinyl and plastic are only for insulation, Jon......neither is effective for shielding.
Great video Doug. Trusty Rusty never fails.
Thanks, SS. Like death and taxes, Rusty always comes through in the end :)
I sure miss working on vacuum tube stuff, I am slowly getting back into it but on a very small scale due to space & money.
Those 6L6 tube amps can sure punch out the power.
I just found your channel, good video Uncle Doug
Thanks, OG, and welcome to our channel. We hope you find lots of good videos to watch :)
Thanks Doug.
You're welcome, OG :)
Hey Uncle Doug,Really liked this video. Now I know what the problem is with another amp that I have!Thanks again!john
Glad to help, John. Best of luck with your repairs.
Hi Doug love the vids.....I have a Vox AC15 that just started this same thing with the sound of thunder in addition ha ha
Greetings, Mitch. Time to order some new filter caps :)
@@UncleDoug I got some coming cross your fingers I got the problem nailed down thanks again for the knowledge you share with your TH-cam following
Everyone needs a Rusty sniff tester ;-) Searched, but I can't find one on Farnell or RS Components? I suppose no one stocks those any more.
took the words right outta my mouth. Everyone needs a Rusty!
I think they are pretty rare. So if you have one look after it! These things give you so much and not just in the workshop. Priceless item.
Indeed, TT and Cameron. He is my most precious asset (don't tell my wife I said this ;)
Short and Sweet!!! Thank you!
Glad you liked it, Chris.
Great vid. Were they vintage bumble bee caps you pulled out? If they match your new replacement ones and they are not leaking you should use them. Mojo! I'm in the process of putting them in my les Paul along with 50's centralab harness and belden wire with a pair of t tops.
Yes, they were, Tock.....and I intend to test them and add them to my vintage parts stash ASAP :) Regardless of their tone capabilities, they really look neat in a circuit.
CIRCLE OF TONE. Stay away from bumblebee caps they are all junk by now.
That dog is a wiz, not to mention its owner. Keep the videos and instruction coming! Thanks.
You're welcome, Whaler. Thanks !!!
Why was the 10uf 250v paper capacitor not tested and replaced? If original, it is very likely leaking DC.
It was tested, Harvey, and checked out OK. However, I may still replace it.
That would be a good idea, these leaks in voltage increase the likelihood of damaging other components in circuit over time with heavy use
Thanks for your input.
Also, an old leaky (electrically) capacitor like that is a fire hazard. Don't want fire damage to the old radio/amp!
Burstein-Applebee PA amp? I was a part counter kid at one store in the mid '70's but I don't remember seeing anything like this.
Thanks Uncle Doug and Rusty.
You're welcome, AT :)
Nice job on getting rid of the 120hz hum. I wish I could understand electronic circuits. I have a pair of 1959 Stromberg Carlson 6550 push/pull mono block tube amplifiers that are actually NOS never been used in original boxes. I can’t find a technician in New York State that can go through them I have really very little education in regards to electronics. Sure wish I could find a technician to test this so I may use them as home audio mono blocks.
Thanks :) Contact Mike@mendittoamps.com, Greg. He's in your area and can probably help you.
It was playing"hum along with Herman"😆😆😆
Not a good sound to hear, now it's Dynamite. I Love you Uncle Doug and I LOVE your Channel and Rusty is a GREAT Puppy Dog 🐕
Wow, thanks so much, Randy :)
Rusty sneezing. yes That can was shot. I've seen 2 4 section caps with all 4 sections read less than 200ohms .They both were scorched and someone had put a 20 amp fuse in place of a 3a. very lucky the transformer was still ok!!!! Thanks for your videos. They help me in areas im short in
No pun intended I hope :) You're welcome, William.
I love the bit about your dog at the end. Dogs are great!
Yes, they are :)
Complete noob here. When you are using the multimeter [on Ohms] I can see the positive test lead but where is the the common lead? Don't you need both to complete a circuit for a proper read? Please let me know. Thank you kindly
Yes, both leads must be connected for all measurements, Fed. Perhaps the black lead was connected to the chassis and out of sight.
HEY! Do you do this for a living? Because I got a record player that has a really bad hum and I know it’s the capacitor, but only if you live in Texas, because that’s where I live
No, it's mainly a hobby to supplement my Social Security, T44. The bad news is, I don't work on record players.
@@UncleDoug aww man, that’s too bad, because this thing hums worse than that radio you showed, and it makes the music that comes from the vinals sound terrible
And the worse part is that I don’t know how to fix it, or even take it apart
The filter caps that were in my 65 PA head were also just trashed lol, ive replaced them im just waiting for new grid capacitors to come in
Thanks for sharing, Sean.
What do you surmise caused that cap to totally fail ?
Probably age and lack of use. Electrolytics tend to dry out and fail as they age, particularly if they are not used frequently.
this comment is made prior to that can capacitor, caps like that are the main reason prior to such loud hums, because the electrolytic fluid in that capacitor is no more, there is hum as a result of it's high resistance, usually the resistance in the can electrolytics are low and able to be used as long as they are neither leaky or dry because it helps keeping the tubes inside(if any) from red plating
Thanks for your input, SD.
One upside: they do help us to appreciate the not-too-awful capacitors.
I never considered that, M. Thanks :)
I’m amazed that you comment on just about every comment. That must take a lot of team!
I spend about 4 hours a day responding to questions and comments, Tim.
Thanks for this, Doug. Always informative and enjoyable. BTW, where is Jack?
You're welcome, Shaun. Their contracts stipulate occasional individual starring appearances. Jack's turn is coming up.
Are all the resistors all around and between the tube sockets factory wiring? Another great video!!
that's what I was thinking too
Thanks, Big Joe. The resistors appear to be scattered about, approximately wherever they are needed. This was really point to point :)
Is this a series filament amp? I don’t see a power transformer.
Excellent demonstration of the Rusty test! Very nice raunchy sound, is the bias set cold? Was Jack on camera for this one or relaxing on the couch. :))
Thanks, Andrew. The PD was 16.5W for metal 6L6's.....which is just about optimum in my book. I think the guitar input was overdriving the octal pre-amp, but the moment I heard the resulting tone, the Kinks came to mind :) Jack is on hiatus for a couple weeks, studying astrophysics at MIT.
Perfect for Kinks songs...
Great video. Im glad Rusty is finally letting you use his name on the channel. I assume he will take 50% royalties from anything copyrighted......
Actually, his contract calls for a 70/30 split (to his favor), since he is, as he always reminds me, the brains of the organization.
Man, he always comes out ahead. His handsomeness is what does it for him.
.....and his winning smile :)
Uncle Doug Right you are! You guys have a great night! Thank you for the great videos. I am an industrial electrician/maint tech but limited in electronics. With a few good tube amp books and your truly great videos I am gaining more and more knowledge about my beloved tube amps. Thank you very much for sharing your wisdom and knowledge!
You're welcome, Dave. We're glad to hear the videos are helpful. Our best to you and yours.
Hi Uncle Doug - thanks for all the great videos - I don't even have a tube amp but I still enjoy them ! Did you have to train Rusty to be a component sniffer ? Or is it one of those things some dogs are just born with ? My dog demonstrates no obvious diagnostic skills. Maybe I could start her out with some dog-bone resistors and work up from there ?
You're welcome, Christopher. Rusty was just a natural-born component sniffer. Even as a pup, he would sniff and bark at faulty transformers and electrolytic caps. Jack, on the other hand, is slowly developing his cat scanning abilities, but he's still young and I'm optimistic about his future in diagnostics. Perhaps your dog would be more interested in circuitry if you started using bacon as shrink-wrap :)
My electronics teacher showed that a new electrolytic cap will have a low resistance until it charges to the meter's output voltage. However, that 120Hz hum says bad caps in billboard-sized lettering. Loud distortion at 2 means high input level. Guitars put out 0.5v, microphones, about 0.05. Possibly a second input for a clean signal is needed? It's what I'd do, anyway.
Thanks for the helpful input, DA.
Anytime :)
Hey, Dopey! When installing axial lead capacitors ROTATE them so the capacitance and voltage markings are visible. 🤨
If you watch any of my more recent videos, I make a point of doing this......but more importantly, on this channel, we don't begin our comments or responses with insults, like "Dopey". If you wish to participate in correspondence, then please heed this rule.
Awesome Vid uncle Doug... nice ending!!
Thanks, T73 :)
Hey Mr Doug build some more amps please sir LOL. I'm electronically zero'd but you and another guy, Tony McKenzie, on YT inspired me to try so I ordered a MOD 102+ kit complete with very explicit instructions (Very). I took my time and was quite successful. I've been building speakers for years so I ordered a british celestion GH12 or some such and boxed it. I'm really impressed with myself. It sounds better than either my fender or my marshall. LOL. Thanks Doug.
You're welcome, Jim. Congratulations on the successful completion of your project :)
I love Rusty. And your videos are top notch as well.
Thanks ,Mike :)
My goodness Uncle Doug! Did they go bad or were they just junk in the first place?
they do get bad over time...they simply dry out. and while they do so the aluminium foil which forms the capacitor may come so close that they eventually shorting out if you apply any voltage on the terminals. Or the electrolytic which forms the insulation between the foils become some kind of plastic and makes that very thin foil cracked and then there is no capacitor no more just two terminals connected to nothing....
Well said, TC. Thanks :)
+TubiCal thank you!
I observed one electrolytic cap go in a mac 2120. Like a mini volcano. Very cool. It had a very peculiar smell. Is that smell always the same when they go or when they are thinking about it? I've noticed that smell on some other vintage gear.
The electrolyte, when badly overheated, does have a peculiar odor.
Since you're talking about caps..
Doug, I've ordered a HI-Fi tube amp kit and on the power supply circuit the schematic says I need a 150uF/450V Electrolytic cap just after the choke..
Question is, can I stick in there a 470uF/450V cap, providing it fits, or is that overkill and/or detrimental?
How about a 500V or 600V cap at 1000uF?
LOL.
Guess what I'm asking is..can I install the biggest cap I want?
Back in the 90's I scratch-built a 12V brick-style power supply using the biggest transformer and caps for the voltage regulator I could buy for a secondhand car amp I used to drive my scratch-built speakers which sounded good and loud in my room and hadn't any trace of hum/buzz.
I'm not a total noob to electronics but electron tubes/valves are new territory and I'm finding them so fascinating!
I'm loving the idea that, once completed, my amp won't have a single semiconductor within it and will be as far removed from digital as possible, apart from the on-off switch!
Loving your videos even though they center on guitar amps mostly but the principal is the same and I'm soaking them up.
The simple answer is no, Dennis, you can't arbitrarily increase the values of capacitors in a power supply. Engineers dictated the proper values and their choices should be followed. A slight increase, i.e. 22uf instead of 20uf, is OK, but you risk damage to your rectifier tube (and gain nothing) if you greatly increase filter capacitance.
This is what you found in old amps....the other day i found some light bulbs wired in as cathode resistors for the output tubes in a *fixed negative grid biassed* amp....if you push that amp very hard they do light up and add some resistance in this path and save the output tubes from dissipating too much power.....
I believe the Hammond AO-44 (or perhaps the AO-39) uses some light bulbs as variable ballast resistors. It's actually a very clever solution, probably developed before varistors appeared on the scene.
Give Rusty a pat on the head and a cookie for a job well done !!! Way to go Rusty!!
I did, Jake, and he ended up stealing the entire box of cookies and hiding under the car to eat them all :)
Hi Uncle Doug, stupid question time... I noticed in a few cases now that you have chosen to replace cans with axial electrolytic caps. Is it based on availability or is there another reason? I recently replaced all the cans on a Hiwatt DR-103 and used all new cans that were readily available to me. Just curious.
As always, great video! Give Rusty a scratch for me.
This was a customer amp, JC, and cost was a definite consideration. The separate caps were much cheaper than a replacement can.....and I had the individual caps on hand, while ordering a replacement can (if one could be found with the proper values) would take several days. If this was a Blackface Fender Deluxe Reverb I was restoring to keep, I would order and install the proper can caps.
+Uncle Doug : completely understand and it makes sense. I have had experiences where I could not the original parts and used what was available and everything was just fine. Project economics drive many considerations. Speaking of considerations, excellent job in your recent capacitor series installment explains the differences, why's, and applications for various capacitors. All the best!
Thanks so much, JC. We're glad you enjoyed Part 1 of the Capacitor series.....more to come :)
great work as always Doug. I would love some instruction on working with load lines
Thanks, Otter. It could happen....I just need to do some research and figure out a way to explain it clearly.
+Uncle Doug awesome, thank you
You're welcome :)
Wow, that's a pretty good sounding 2 on the volume knob. o_O
With my small video camera microphone I have to be careful not to overdrive it too much, or the resulting distortion will give a false impression of the amplifiers true tone. The "2" was indeed rather loud :)
nice video.. Did you trace down the hum in the ampeg jet?
Not yet.....too many distractions :)
Is humm sound on old recivers is caused by bad capacitor?
Watch my video on determining the frequency of the hum and using this to help determine the cause.
If you don't mind me asking what area are you in? I'm in long beach, ca and so hard to find good techs that know much about this stuff. I had a great one for years...Red Rhodes...also a great steel pedal guy ( sweet baby James) but he's gone now unfortunately. I collect many old fender amps but always in need of repair. Thanks and for
your videos! Hi to Rusty!
Rusty and I are in West Texas, David, about 850 miles east of you. We're very flattered that you would seek our help, but we've retired from doing outside work. Hopefully, you can find another trustworthy tech in your area. Best of luck.
Ever hear of budroc capacitor ? I have a 1955 Gibson guitar with one
I think it’s possible not the right one ? Thanks for ur video 😊
I have not heard of that brand, FD.
looking at your videos, i don't see a lot of star grounding in the amps.
how common is it? and in your opinion, how important is it?
I've only built a handful of tubeamps, but i've always stargrounded.
having caps connected to separate points on the chassis will make currents run in the chassis itself, possibly leading to noise, no?
am I wasting my time stargrounding?
I can't say that you're wasting your time, Borgar. Many very knowledgeable people swear the star grounding is the only way to go. In my own experience, using both star grounding and (good, logical) multiple-site grounding, I don't really hear much difference. My recent Supro build (see the video series) uses what I call "common sense" grounding (not star) and it is dead silent. Yes, there may be tiny differences in potential within the chassis, but they are primarily DC......which is silent.
I know, it's not that I'm going to use the amp without the guitar plugged in, I was just worried as to why it was doing that..it's kind of strange.the thing that's really bothering me is the short duration of crackles and pops at startup .im worried to use the amp because I heard of the caps are bad causing that then the power supply can be damaged if I use the amp with bad caps?
The primary indicator of failing filter capacitors is a 120Hz hum (i.e. double AC supply frequency). If you are truly concerned about the noises, then take the amp to a qualified technician and have them check it out.
Hey there Doug! great videos! I love them. I was wondering if there are like a couple of precautionary steps (in summary) for working with high voltage amplifiers? I know that one must drain all the capacitors by using a resistor and shorting but besides that is there any other dangers lurking around? I have had questions like if you touch a transformer (like those big ones outside some amplifiers) can you die? should you cover them all the time? Ive been wanting to tinker with tube amps but im afraid I do not have the sufficient knowledge for that. Thanks again for the great and informative videos
Safety precautions, including how to make your own capacitor-draining tool, are included throughout the videos, 39P. You really need to watch and acquaint yourself with all of them before touching any of the wiring or internal components of a circuit. A couple of quick suggestions: Never be grounded (skin touching concrete, pipes, etc.), and never touch any circuit with both hands (keep one in your pocket).
Uncle Doug Thank you for those tips! Ill watch your older videos! so far the ones ive seen have been really useful.
You're welcome, 39P. Best of luck :)
Uncle Doug can you advise what to look for when buying a tube tester on Ebay?
Their circuitry is extremely elaborate, they are difficult to re-calibrate, and they are easily damaged by shipment and rough handling. I would suggest a Hickok tester, from a seller with flawless feedback who will accept a return, if necessary. Good luck.
thanks for the video...when that hums like that is more current being drawn thru the circuit than is designed to?
You would think so, but the Current Limiter bulb did not illuminate. The capacitor can got real hot, however, so there is definitely some current flowing through the leaky caps (which had become resistors) to ground.
I heard a noise like that just before that amp I told you about caught on fire...It was just a little fire that went out within seconds... I big ceramic resister blew up and a couple of others looked cooked.
I'm learnin the hard way but i don't mind...thanks again for these videos. ..and rusty was right bout those can capacitors they stink!
Yes indeed, if you don't pull the plug quickly on a roaring hum like the one in the video, something is either going to catch fire or explode.....and you can't believe the mess an exploding electrolytic capacitor can make :( Keep on learning, YR. Often learning the hard way makes the longest-lasting impression.
I have an old Precision Electronics 2-6L6 amp. It used to work but is on the blink now.
Hopefully the electrolytic caps in it are better than the ones in mine were :)
Hi Uncle Doug! I love the videos you are posting. I know you have said you get your parts at antique supply and power supplies at another site. I haven't had any luck finding an old mallory capacitor (500V/30 MFD, 500/10, 450/10, 450/10) that would help me fix a 4 channel Rauland 2135 pa amp. Is there somewhere else you go to find anything along this order? Sorry if you answered this question in another video, i am still working my way through them.
It's often impossible to find the exact can cap you need, Erik, which is why I generally resort to installing individual axial caps within the chassis, leaving the old can in place for looks. I know of no other good sources for the can-style capacitors.
Thank you for your response. Finding the original would be a one in a million at this point lol. After more hunting and calling several manufactures. The problem is finding a replacement cap 500v/30. I was able to find a 450/30 and a 600/30 and 450/10 for the others. I am not sure what one to go with. Does the voltage rating affect the tone or have any ill effects on the transformers? If a surge pass thought the cap at 600v that would normally fail with the original, would i be doing more damage than good using a 600v cap? Maybe add a 500 v fuse to protect the rest of the amp? Any thoughts on what to do when you can't find the right volt value capacitor are appreciated. Thank you for your time.
Also i was able to find a 500v/40uf 500/20 500/20 500/20. Would this be a better option? That was the closest i could find for a can replacement.
It would probably work just fine, Erik.
Thank you. Your videos are very informative and funny. I get your sense of humor.
Looking in the circuit with another few years research in my brain, I see Tiny Chief caps... those are paper/oil type, and like Bumblebees do go bad with age... did those get tested too?
Yes they did, DK, and (surprisingly) seemed to be fine.
Cool deal. I'm re-capping a 1979 Peavey Mixer... it had 120hz whine.. and since it's been an on-the-road concert mixer, it's seen and heard a great deal. There's only 350 or so Electrolytic caps. Some are bulged, some leaked, all are getting changed... Fun Fun Fun... Tedious as heck.
Definitely not a fun task, DK. Best of luck with it.
Got it all done (350+ caps) ... it's a long boring video. However, I recorded my DIY leslie speaker in Stereo, and that worked great. My DIY leslie is a little different than yours... but not too much. we started with the same drum... I had a 10" speaker, and a relay to use as a foot switch on/off. All that stuff is posted.
Doug, got a question. I'm starting to do my own amp work. My first project is replacing the filters on my Marshall JCM 800 50W amp, and biasing new power tubes after the cap job. I have a tube bias adapter, so good there, but the filters came with two smaller caps, and I wanted to check to see if those, still on the board are in spec. Can these be checked in circuit with a multimeter? Or do they have to pulled from the board and tested, or can an in-circuit ESR meter tell me what I need to know? If the proper way is with an ESR meter, any suggestions on one that will work for amp repair or maintanance? I am looking at a few for sale, but need to make sure I'm looking at ESR's that can do amp work ranges...I just want to be able to check if they are in spec within tolerance. Thanks!!!
You really can't fully test capacitors with a multi-meter. Even if the capacitance reading seems appropriate, the capacitor could still be faulty. ESR meters are specific for electrolytic caps and much better at spotting failing ones, but they don't fully charge the cap to operating voltage, which is about the only absolute way to judge them. I have an Anatek Blue ESR meter and use it all the time. It may not be the absolute most-thorough method to sniff out failing electrolytics, but it very practical and effective. You can use an ESR meter to measure all electrolytics in circuit, unless they are in parallel.....which is quite rare.
Thanks for the reply. So I would be able to test electrolytic caps in circuit with a decent ESR meter? I was looking at either the Anatek Blue or the Signstek MESR V2. I was just looking for a way to test electrolytics to see if they need replacing while still in circuit on my vintage amps. De-soldering would not be a big deal, but was wondering if it can be done reliably enough in circuit with either a multimeter, or a decent ESR meter. I'm going to be looking at as many videos as I can to see how testing on caps in amps like mine are done to determine whether or not they need replacing. I see you have a vid on this with the Blue, so I'll be posting there. Like I said, replacing the filters is straight forward enough, and re-biasing the JCM 800 out put tubes looks easy enough, but diagnosing the electrolytics has me baffled right now.
I believe my Hiwatts and Sound City amps on the other hand, ( correct me if I'm wrong please..) dont have bias pots and will need to adjust bias through the resistors. Thats for another time. Right now the JCM is the easiest platform to start with. Thanks for the replies Doug!!!
It’s like if Steve Martin fixed guitar amps! Uncle Doug is hilarious great videos too very informative. Tell cousin Jack congratulations on being an astrophysicist! And I think Rusty’s only pretending to sniff the bad caps out y’all... he can probably only tell due to his esp
Thanks so much, Joey. Glad you enjoyed the video :)
how did i miss this?? outstanding! to include a RustyScan as well!
Keep looking, Andy, and I'll bet you find even more unseen videos :)
Hi Douglas,
Was that four electrolytic smoothing capacitor canister, incorporated into the PE30 amplifier, manufactured by Hunts Capacitors of London (now mercifully no longer in business)?
I ask this as Hunts capacitors had a reputation for being unreliable. I always evict the blighters whenever I see them beneath a vintage radio’s chassis.
What is that ESR meter you use? I’m curious!
73 de Phil.
I'm not sure, Phil. The only unusual characteristic was that it was abnormally tall.....about 6". The amp was picked up by the owner yesterday so I can't check it. I use an Anatek Blue ESR meter. They have a great website, excellent service, and great products.
how did they check out for capacitance, cool little amp by the way? :)
That's a good question, Jozef. I ran every test but that one. The amp is gone now, so it's too late to check, but I would imagine their capacitance to be quite low....if any.
Hey Doug, thanks for the videos 😃I have a question regarding a SS amp. I have a Marshall MG 15. The Neutral prong on my plug broke off and it heated up pretty good. I noticed the wiring coming out of the transformer got a little cooked. After going through a couple of fuses, i fixed the plug, but now I seem to be getting a lot of "what i thought " 60 cycle hum. A person i was talking to said i probably burnt out a filter. Was he talking about a filter capacitor? Do SS amps even have filter capacitors? Im wondering if what i hear is actually 120 cycle hum... great channel by the way. I am learning a lot about how to work on my Fender Hotrod Deville (my "real" amp) through your channel.
By the way, i like the sound of that PA too 👍🔥
There is no telling what harm might have been done by overheating, Kyle. Yes, SS amp power supplies use filter capacitors. You might want to get a qualified tech to look it over.
Uncle Doug thanks for the reply. Around my area work is expensive, and questionable at best. Id be better off just to get a new amp, ill just have to do some more research. Got alot to learn :)
Kyle Olin or learn to read an use a meter and solder. i want to build one but damn still not that much cheaper with the good stuff.
Interesting to note that the can cap showed no signs of failure. Bubbling of electrolytic etc.
unfortunately I have cats and they only want to crawl inside amps and do nothing to help me in amp diagnostics.
All hail Rusty!
I could see no external evidence of failure, but Rusty's trusty snout wasn't fooled by the innocent exterior :)
Love the sound of that amp!!
The patient did respond well to treatment :)
What were all of the capacitors that you removed from the amp to bring it back to "as designed"? Was that someone else's attempt to bypass the stock filter capacitor?
Oh, and Hey Rusty, what's up?
I honestly don't recall, Bill. This was years ago, when Rusty was still a pup.
I noticed the cover had a "BA" logo on it. It looks like the Burstein-Applebee brand. I used to buy things from them all the time.
Thanks for your input, Ben.