'76 Twin and '78 Super will be ready for whatever comes next. For more info, Subscribe to this channel, join us at PsionicAudio, or email us at info@psionicaudio.com.
As a veteran musician of over 50 years I get a lot out of your channel. It’s a unique and informed look into these amps. As to your playing. I get a lot more of the character of these individual amps from the way you play than those wankers ar those other (un-named) channels especially pedal channels. As for insights into amps you’ve pretty much steered me into a 70s silver faced giant fender for cost vs build quality / sound. I had a 74 twin in my youth with EVs and swore I’d never drag one of those around again but here we are. Anyway, keep up your good work.
Same thing with grid caps. I once had a 1966 era amp whose 6CA7 output tubes suddenly started to glow like the setting sun. I found that the grid caps on both tubes had failed. They were old wax-covered, paper caps that had become resistors, placing a high positive DC voltage on the grids, forcing the tubes into heavy conduction. Replaced them with newer technology caps - problem solved.
Very educational, thank you. Especially the part about NOT stealing away vintage amp “mojo” by replacing aged caps. I just had my new (to me) ‘67 Super AB763 fully serviced and my excellent tech replaced everything that was out of spec, caps, resistors, etc, and now I have a ziplock bag of old junk bits, and a 55 yr old amp that works like brand new and sounds GREAT! He thinks like you do.👍
A 2fer, follow ups and follow throughs' are what make your videos great. They require the playing the listening the measuring and the due diligence to complete the task. Thanx Lyle.
Another informative video. BTW, use of the same basic riffs is helpful to my ears. Makes it easier for me to hear the differences in tone with different amps. Thank you.
Out of the box, the silver face Super always sounds exactly right to me. I fight for that tone on my other amps and kick myself for not just buying the real deal, which was $2-300 in my teen years.
It’s been awhile since I’ve watched the great Uncle Doug but could you possibly expand just some of the technical aspects like when you spoke about the different cap values under the doghouse and why you chose that value even though the stock ones were different? It always helpful to get reminders of what each component does and how changing the values could be good, bad or really doesn’t matter much in this scenario. Thanks
Thank You! I have this discussion with amp owners continuously, usually resulting in a display of arrogant ignorance by the owner. Heaven forbid you change the tone of their coveted gem. I am going to try to briefly share two of my favorite "poster child" stories with you. First is a Brown Vibrolux broght in for service several years ago, with the complaint of the vibrato not working. The customer had a recording session the next week and he wanted to use the amp because of it's awesome tone and vibrato. He also mentioned in uncertain terms that nothing was to be done except to fix the vibrato. The bias caps had failed, taking the bias so low that the vibrato ciruit could not turn off the tubes to function. The outputs were red plating, and the amp hummed. When I called to explained that he would need caps, outputs etc, he went super nova...... he is no longer welcome in the shop. Bye. Second, and probably the most absurd is a Blackface Champ that was brought in for service by a long time customer. The amp had been purchased at a second hand shop because of its low volume breakup. The pots were noisy, needed a general cleanup; pots, tube sockets, jack etc. It also hummed badly, and was red plating. The 6V6 cathode by-pass cap had shorted, the cathode resistor was swollen and cracked along with the screen power supply resistor. I changed all the bypass caps (others had drifted as well), damaged resistors, etc. I did not mention the filter cap because I knew his frugal thought process would not allow it. I also supplied him with a nice NOS 6V6. Immediately upon testing the amp I could see his displeasure. He commented on how loud and clean it had become, and I told him it was running as it should and showed him the burnt cracked parts. After deciding to take the amp he called back the very next day asking if I still had the old parts? I answered no.....why? He wanted to put them back in one at a time himself until his glorious breakup returned. Thank God I do not drink! Just wanted to let you know I feel ya.
Goes to show their is no accounting for taste … someday someone will hopefully figure out how to replicate the non linear magic of failing parts ! I don’t know how many times I have heard , “man, my amp sounded amazing right before it blew up !”
Bias stability is so crucial to a tube amp, I would argue the cap merits some big money for film or solid tantalum. Not the little jelly beans, but a large mil spec axial as I have used in my beloved 1970 JMP50. It’s a forever fix.
Hey man, I really enjoy your channel. I'm not to far away from you, I'm just across the border (about 85 miles) in Missouri. Do you know J. Church, he use to be at Young Ave. Sound? If you know the old owner of Sounds Unreel studios, we live in the same town. I own a recording studio myself and I learned most of my info from our engineer at Sounds Unreel, her name is Dawn H. and I'm sure you know her. She was the main sound person at BB's. I would love to talk to you at some point and just see how many friends we share.
Excellent point about old, leaky or dried out caps being nothing but trouble. The question remains about carbon-composite resistors - why people insist on using those (NOS and all) when replacing crappy and out of spec ones of the same kind instead of using modern, accurate, reliable and much less noisy metal-film?
Metal film reisistors can sound sterile when there are a lot of them in the signal path for some reason. They are good at withstanding heat. The warmer sounding carbon composition are better in areas where heat, and noise isn't as much an issue.
Carbon comps are okay, perhaps even preferred, for the preamp tube plates and cathodes, but power-supply dropping resistors and output tube screen resistors really should be flameproof, metal-oxide or similar, perhaps wirewound. Carbon comp resistors can actually burn and do damage to the things around them, and therefore I don't like them for high voltage applications, or anywhere they are likely to be subjected to excess current from a short circuit or biasing problem. Carbon film resistors contain less flammable material than carbon comps, so they're somewhat less likely to actually burn, but still, metal film are preferred for power supply circuits.
Tone being so very personal and subjective. My preferences run toward the deeper darker side ie I wouldn’t trade a Fender Super Reverb 410 with good speakers for a Matchless 30.
What are your thoughts on the old bias supply diodes? I know some suggest replacing them since a failure of the bias supply will nuke the outputs. Are the old diodes reliable enough to keep them on the job? I'm a bit leery of the series string of three to get the reverse voltage rating. I'm not seeing balancing resistors, so it appears to count on the diodes leakage being matched close enough that no one diode exceeds it's reverse voltage rating. I'd rather see some higher rated diodes that don't care about balance to survive. I'd think it would help make the amp more bulletproof.
Well, Fender bias supplies usually use just one diode; the main B+ supply, however, uses 6 diodes, three on each leg of the transformer secondary (if it's not being tube rectified, of course). Ideally, or theoretically, each diode in the series-string should have a balancing resistor *and* a capacitor across it (to shunt transients and voltage spikes), but in my experience those diodes rarely fail. I would like to know if Lyle's experience differs.
@@ErikThomasMusic It's not a bad idea to replace the 6 B+ diodes, especially if the amplifier shows any signs of ever having had bias problems or shorted tubes, but it isn't automatically necessary, and I don't know that it makes any particular improvement in reliability to upgrade to diodes with better specs. Lyle's views on this would be appreciated. The bias diode on the other hand being a single device and absolutely critical, I would say just go ahead and replace it.
Just had a 79 twin blow a fuse It was noisy with master turned up past 5 We think the ac voltage is high in that building Any thoughts? Love your work and attitude 🤘
You said the electrolytic that was reading in the nanofarads with high resistance was a virtual dead short. It would seem to me that if the voltage rose on the grid or screen, this would impede the flow of DC voltage in the tube making red plating impossible. As far as I know, red plating occurs when there is too little bias voltage, causing too many electrons to flow to the plate from the cathode,vastly heating up the plate. Were you mistaken in your comment?
@Amp Amp: a tube without *negative* bias on the grid is like a wide-open valve; negative bias is like a throttle control or a "governor" on an engine, and prevents the tube from going full throttle and self-destructing (perhaps blowing a transformer as well). A leaky bias-supply filter cap shunts some of the bias voltage to ground, in this case lowering the negative bias by half. Or, if a positive voltage from the phase-invertor tube's plate(s) leaks through a bad coupling capacitor to the output tube grid(s), it will counteract and cancel some of the negative bias of the grid and lower the overall negative voltage (perhaps even sending the grid positive) causing the tube to conduct too hard.
@@goodun2974 Right. Sometimes the narrative can be confusing to some people. I was simply pointing out that the narrative could be confusing to some. I find this to be happening in some of the videos. It's always good to be clear for the entire audience. Thanks for your comment. I appreciate it.
Hey! I have an idea. Could you do a FAQ video? Just go through all the questions that come up often and answer them. That way you could refer your avid viewers to that particular video and, with a bit of luck, Avid Viewer will find what he is looking for. You do a LOT of videos so trying to find one kernel of information in a grain silo of kernels of information is a daunting task.. If I have a question, like, for example (hint, hint), "What brand of 6V6s do you recommend in a combo amp?", you could just say "Please refer to my highly informative and well thought-out FAQ video!" and all would be well in the world. I know you mentioned that particular topic in a video, but which one? I seem to remember you opined that 6V6 JJs in a combo amp weren't the best choice but I can't remember which tube you thought was a good choice (hint, hint). Oh, it would be such a time-saver if I could just remember which particular video had that particular bit of info in it (hint, hint).
@@PsionicAudio , as far as I am aware, TH-cam's search function doesn't allow us to search for a particular subject, or in this case a particular amp brand or model, *within just one particular channel's collection of videos*. If I'm wrong and there is a way to do this, please let us know.
Lyle , I would like to second his fine idea that you do a FAQ video , please. Please also cover good sources for parts and tubes , I’ve been taking notes but I’m sure I’ve missed some. Thx Cheers Bebop
Loosing chassis grounding is never a good thing. Then all it takes is one leaky capacitor, or tube to electrocute you. There are too many bad things that can happen with a cord like that one.
@@qua7771 , also, a leaky "death cap" can be a shock hazard all the way up to the guitar strings if the amp doesn't have a grounded cord. Many guitarists are unaware that if the amplifier is wired right and has a good earth ground via the power cord, the polarity switch and/ or death cap are *unnecessary*. Occasionally, one also encounters an death amp with voltage leaking from the power transformer windings to the chassis, yet another reason why a grounded cord is a necessity..
@@qua7771 , Ditto. I'm a tech, not a gigging musician, and any amp I work on gets a grounded cord and the death cap removed (and polarity switch disabled). No exceptions. A good safety test for the non- technically-inclined musician is to plug their vintage amp into a ground fault circuit interrupted (GFCI) outlet in the kitchen or bathroom, and flicking the polarity switch if the amp has one, to see if it trips the built-in breaker. If it does, you have a dangerous situation that needs to be addressed before you use the amplifier
Think I'm hearing what you meant about the TMDR v these amps when snapping the E or B string....? The TMDR hasn't that ring or sustain...? Think the TMDR has that compressed...? Probably describing this inadequately 😉😎👍
@@PsionicAudio It'll be interesting a few years from now when they come in for repairs, to see what you might be able to do to the TMDR once you get inside of them😉😎👍
I could change the ICE Module or resolder a bad pot/jack connection. Or swap a board if Fender makes them available to non-authorized service centers*. Other than that, they aren't "tweakable" - any more than I can change the innards of this laptop's CPU. * I've been asked to be authorized service for a lot of companies but I decline. Not worth the paperwork, the second guessing, the lame pay, or the long payment cycle.
@@PsionicAudio No fun in Mudville as far as the Tone Masters are concerned 😉😎👍 The future of tech is proving to be limiting indeed...? No worries though..we have others and you to help us😎👍❤🖖
Goodevening....i have question.....i have a Fender Quad Reverb My Capacitor Mallory 25uf 25v has been damage what capacitor and what value of UF and value of Volts of the capacitor replace to the orginal capacitor( Mallory 25uf 25v)... Thank you Very much...
ALL the 25uF/25V caps should be charged out. They’re all 45 years old at least. 22uF or 25uf doesn’t matter, anywhere from 16V to 63V is fine. Sprague, Vishay, and MOD are all good choices.
Whenever I see a wiring harness in these later CBS Fenders that have the white wire coiled like a spring around a bunch of other wires, I ask myself, how necessary was/is this, to presumably prevent oscillation or radiation of noise fields? Is it really that effective, or isn't there a better way to go about fixing the issues with the lead dress in these amps than that twisty mess? I mean, if it's effective, fine, I guess, but damn, it looks fugly! My mild OCD doesn't like it one bit.
I made an amp with very neat looking wiring, but it sounded horrible. It had all sorts of problems including ghost notes, frequency cancellations, muddy lows, and high frequency spikes caused by crosstalk oscillations. I had to tear down all the neat wiring, and do it over in a more electronically mindful way. That was a learning experience.
@@qua7771 , generally, running a bunch of closely-spaced wires together and/or bundling them together in a harness or loom is a recipe for noise and oscillation unless done very specifically so that the magnetic fields cancel each other out. I've never seen anybody else ask this question and publicly examine/discuss how and why the wiring was done this way in those later era Fenders. Next time I work on one I'll have to try and analyze which circuit paths are contained within that bundle.
If I recall correctly it was used as a type of shielding separating the b+. Wrapping it with the ground would help control noise even though it is a loose spiral.
@@goodun2974 Wires can become microphonic as well. It seems like an odd phenomena, but consider there are electromagnetic fields present. Tube amps have all sorts of strange anomalies.
More like having a 1959 Chevy 348 6 pack Impala SS with the original tires, brakes & hoses on it. Let's go for a ride! Let me update my life insurance policies first. I'll take that ride with the old oil. I can rent machine shop time & rebuild a motor, but I can't set my own broken bones.
Lyle, I gotta disagree with you. Red plating due to caps is caused by leakage, not high ESR. Leakage may not appear in the testers you used. (Leakage is parallel resistance, not series). High ESR means the cap isn't passing signal, or doing as good a job at filtering as it should (even if the capacitance value is correct). Sometimes leaky caps will show as higher capacitance as it takes longer to charge them. So caps that show unusually high are suspect. Either way, you definitely had an open cap, and that's enough reason to change both. I'm with you on the rest of the lecture.
Ah, but high ESR causes caps to generate heat which can cause/exacerbate cap failure. So an indirect cause of the failure but a correlated symptom. If it makes you feel better, I’m not satisfied with how I presented that section. Was trying to show how a visibly good old cap could fail with serious consequences, but I didn’t want to get too in the weeds. I didn’t strike the right balance.
@@PsionicAudio What you say about ESR and heat is very true of filter caps in a switching power supply. That's what makes selecting the right cap for switchers important. I'm far less convinced that high ERS creates heat in audio signal coupling applications. Yes, a cap that "tests good" for value, can certainly be bad. To truly test a cap, you need to do at least ESR and leakage. Maybe value as well. Of course, if it's really leaky, it can be spotted with a live in-circuit test.
@@russellhltn1396 , I have seen plenty of domed, bulging-top caps in the lower-voltage power-supply and protection circuits of 1970's/80's solid state audio gear, which doesn't use switching supplies. If the cap in question isn't located near a hot resistor or regulator, then either it failed from ripple currents or just degraded over time and started generating internal heat as it transitioned from a "purely" capacitive device to one with ever-increasing current flow/voltage drop and the attendant internal heating. Also, sometimes the cap doesn't physically dome or bulge but the shrink-tube label will shrink back even though there's no hot components nearby. It's usually a sign of internal heating.
@@goodun2974 Oh, no doubt. I think you're trying to disagree with my comment on ESR causing heating in audio applications. But I think instead you've made a case for heating though leakage.
people really criticised you for "noodling"??? 😂😂😂 so clueless hahaha obviously gotta test the amps fairly extensively with a multitude of techniques as you've explained. there isn't time to play thru a set list of songs. I know for a fact that you don't care either way but I actually enjoy listening to you doing tone tests. seems like alot of tech guys are usually pretty decent players, I think that partially comes from always being around instruments and having expertise on finite details of how they work. it's probably a lot of fun playing different amps everyday after you fix them up. cheers 🍻
Cap makers spec 7 years for peak useful life . After 7 years to 10 years non film cap fall off from the cliff . film caps do last longer LCR meter will clearly show that elec caps fall well out of spec after 7 to 10 years period . I hope people listen to your expert view of the real deal on these amps. Caps are not red wine they do not age well. Hater just keep hating as it is said here in the South . Your playing fills the bill for it use.
Are you saying they have a shelf life even if unused? I would think that electrolytic filter caps would last substantially longer in an amp that rarely gets used, compared to one that is gigged out daily. Secondly, spec sheets show the tested lifetime rating of various caps based on industry standards. I generally look for caps rated for over 10,000 hours, low ESR, and high ripple current. This is the first I've heard of them having a 7 year life expectancy.
"Bragging that you got a '66 Mustang with the original oil." - Love that analogy.
As a veteran musician of over 50 years I get a lot out of your channel. It’s a unique and informed look into these amps. As to your playing. I get a lot more of the character of these individual amps from the way you play than those wankers ar those other (un-named) channels especially pedal channels. As for insights into amps you’ve pretty much steered me into a 70s silver faced giant fender for cost vs build quality / sound. I had a 74 twin in my youth with EVs and swore I’d never drag one of those around again but here we are. Anyway, keep up your good work.
Same thing with grid caps. I once had a 1966 era amp whose 6CA7 output tubes suddenly started to glow like the setting sun. I found that the grid caps on both tubes had failed. They were old wax-covered, paper caps that had become resistors, placing a high positive DC voltage on the grids, forcing the tubes into heavy conduction. Replaced them with newer technology caps - problem solved.
I wish all politicians were as honest as you are. You are providing an excellent video library for future generations. Cheers Lyle!
I appreciate Lyle's honestly as well.
If politicians started being honest they would have to go into hiding.
lol no such thing as an honest politician. Thats an oxymoron
If they were they would never get elected!
Very educational, thank you. Especially the part about NOT stealing away vintage amp “mojo” by replacing aged caps. I just had my new (to me) ‘67 Super AB763 fully serviced and my excellent tech replaced everything that was out of spec, caps, resistors, etc, and now I have a ziplock bag of old junk bits, and a 55 yr old amp that works like brand new and sounds GREAT! He thinks like you do.👍
Love your videos I learn something from each one of them. Thanks for putting them out there for us
Really appreciate you and these videos Lyle. Thank you so much. Learning, learning, learning. Thank you.
Thanks again Lyle aiways a pleasure to tune in always learn something
Nice job, you have the "Mojo" in your ears and that is a real bonus that works in your favour.
I’ve watched this session three times to avoid asking questions. It is easier to learn by watching more than once. Thanks for the knowledge Sir.
Preach it!.. superb electronics and music repair channel.
A 2fer, follow ups and follow throughs' are what make your videos great. They require the playing the listening the measuring and the due diligence to complete the task. Thanx Lyle.
Another informative video. BTW, use of the same basic riffs is helpful to my ears. Makes it easier for me to hear the differences in tone with different amps. Thank you.
Thank you for explaining how our favorite recordings from days past were made with new or next to new amps. Even Tweeds were sort of new in the 70s.
I dig your playing/noodling, I been trying to figure out that one lick you do alot, I haven't yet but I keep tryin...another great video....thank-you
Love it buddy...
Lmao oh no my tender sensibilities! You’ve hurt my tender sensibilities! 🤣🤣 great video keep them up!
Those two amps sound gorgeous.
Btw, your noodling is excellent. I’m from Kzoo originally, you’d fit right in.
i like the vintage Mustang analogy
Out of the box, the silver face Super always sounds exactly right to me. I fight for that tone on my other amps and kick myself for not just buying the real deal, which was $2-300 in my teen years.
It’s been awhile since I’ve watched the great Uncle Doug but could you possibly expand just some of the technical aspects like when you spoke about the different cap values under the doghouse and why you chose that value even though the stock ones were different?
It always helpful to get reminders of what each component does and how changing the values could be good, bad or really doesn’t matter much in this scenario.
Thanks
Thank You! I have this discussion with amp owners continuously, usually resulting in a display of arrogant ignorance by the owner. Heaven forbid you change the tone of their coveted gem. I am going to try to briefly share two of my favorite "poster child" stories with you. First is a Brown Vibrolux broght in for service several years ago, with the complaint of the vibrato not working. The customer had a recording session the next week and he wanted to use the amp because of it's awesome tone and vibrato. He also mentioned in uncertain terms that nothing was to be done except to fix the vibrato. The bias caps had failed, taking the bias so low that the vibrato ciruit could not turn off the tubes to function. The outputs were red plating, and the amp hummed. When I called to explained that he would need caps, outputs etc, he went super nova...... he is no longer welcome in the shop. Bye. Second, and probably the most absurd is a Blackface Champ that was brought in for service by a long time customer. The amp had been purchased at a second hand shop because of its low volume breakup. The pots were noisy, needed a general cleanup; pots, tube sockets, jack etc. It also hummed badly, and was red plating. The 6V6 cathode by-pass cap had shorted, the cathode resistor was swollen and cracked along with the screen power supply resistor. I changed all the bypass caps (others had drifted as well), damaged resistors, etc. I did not mention the filter cap because I knew his frugal thought process would not allow it. I also supplied him with a nice NOS 6V6. Immediately upon testing the amp I could see his displeasure. He commented on how loud and clean it had become, and I told him it was running as it should and showed him the burnt cracked parts. After deciding to take the amp he called back the very next day asking if I still had the old parts? I answered no.....why? He wanted to put them back in one at a time himself until his glorious breakup returned. Thank God I do not drink! Just wanted to let you know I feel ya.
Goes to show their is no accounting for taste … someday someone will hopefully figure out how to replicate the non linear magic of failing parts ! I don’t know how many times I have heard , “man, my amp sounded amazing right before it blew up !”
Bias stability is so crucial to a tube amp, I would argue the cap merits some big money for film or solid tantalum. Not the little jelly beans, but a large mil spec axial as I have used in my beloved 1970 JMP50. It’s a forever fix.
Another great video. Can you tel me all the components I need to fix the common problems on a blues jr
Your playing is very much better in this vid Lyle :)
Um, thanks? ;)
It varies by time of day, whether I’m warmed up, and red light syndrome.
we have similar noodling. feels very familiar when you test amps
It appears that this particular amp still has the unobtanium washer that is usually missing from underneath the pilot-light bezel.
But what about my tender sensibilities? Lol. Great videos.
what did you set the bias to on the twin ? I have a similar one and just got a quad of the same tubes.
Hey man, I really enjoy your channel. I'm not to far away from you, I'm just across the border (about 85 miles) in Missouri. Do you know J. Church, he use to be at Young Ave. Sound? If you know the old owner of Sounds Unreel studios, we live in the same town. I own a recording studio myself and I learned most of my info from our engineer at Sounds Unreel, her name is Dawn H. and I'm sure you know her. She was the main sound person at BB's. I would love to talk to you at some point and just see how many friends we share.
A curious question if want or can answer for me. How can a speaker while it's cone is vibrating produse so many different frequency sounds at ounce.
Deep subject. There are long white papers on this. I can’t distill it into a comment, sorry.
Also thinking of '78 Super's screen node. 497V sounds right for an UL model where screen caps are same as plates. Is that what it is?
Yeah, stay tuned for my solution.
Excellent point about old, leaky or dried out caps being nothing but trouble. The question remains about carbon-composite resistors - why people insist on using those (NOS and all) when replacing crappy and out of spec ones of the same kind instead of using modern, accurate, reliable and much less noisy metal-film?
Metal film reisistors can sound sterile when there are a lot of them in the signal path for some reason. They are good at withstanding heat. The warmer sounding carbon composition are better in areas where heat, and noise isn't as much an issue.
Carbon comps are okay, perhaps even preferred, for the preamp tube plates and cathodes, but power-supply dropping resistors and output tube screen resistors really should be flameproof, metal-oxide or similar, perhaps wirewound. Carbon comp resistors can actually burn and do damage to the things around them, and therefore I don't like them for high voltage applications, or anywhere they are likely to be subjected to excess current from a short circuit or biasing problem. Carbon film resistors contain less flammable material than carbon comps, so they're somewhat less likely to actually burn, but still, metal film are preferred for power supply circuits.
Tone being so very personal and subjective. My preferences run toward the deeper darker side ie I wouldn’t trade a Fender Super Reverb 410 with good speakers for a Matchless 30.
I bet your get a lot of views on an FAQ vlog episode.
Have you worked on any Fender SuperSonics? Are they any worse than a HRD?
Better than HRDs but usually noisy. Faults more like the reissue series.
Some say, red plating tubes sound the best. Sounds expensive to me :)
What are your thoughts on the old bias supply diodes? I know some suggest replacing them since a failure of the bias supply will nuke the outputs. Are the old diodes reliable enough to keep them on the job? I'm a bit leery of the series string of three to get the reverse voltage rating. I'm not seeing balancing resistors, so it appears to count on the diodes leakage being matched close enough that no one diode exceeds it's reverse voltage rating. I'd rather see some higher rated diodes that don't care about balance to survive. I'd think it would help make the amp more bulletproof.
Well, Fender bias supplies usually use just one diode; the main B+ supply, however, uses 6 diodes, three on each leg of the transformer secondary (if it's not being tube rectified, of course). Ideally, or theoretically, each diode in the series-string should have a balancing resistor *and* a capacitor across it (to shunt transients and voltage spikes), but in my experience those diodes rarely fail. I would like to know if Lyle's experience differs.
@@ErikThomasMusic It's not a bad idea to replace the 6 B+ diodes, especially if the amplifier shows any signs of ever having had bias problems or shorted tubes, but it isn't automatically necessary, and I don't know that it makes any particular improvement in reliability to upgrade to diodes with better specs. Lyle's views on this would be appreciated. The bias diode on the other hand being a single device and absolutely critical, I would say just go ahead and replace it.
Just had a 79 twin blow a fuse
It was noisy with master turned up past 5
We think the ac voltage is high in that building
Any thoughts?
Love your work and attitude 🤘
Unless it has been fully recapped in the past five years, I wouldn’t hazard a guess.
Yea someone a long time ago tried to turn it into a black panel circuit and we had a tech bring it back to spec about 4 or 5 yrs ago
You said the electrolytic that was reading in the nanofarads with high resistance was a virtual dead short. It would seem to me that if the voltage rose on the grid or screen, this would impede the flow of DC voltage in the tube making red plating impossible. As far as I know, red plating occurs when there is too little bias voltage, causing too many electrons to flow to the plate from the cathode,vastly heating up the plate. Were you mistaken in your comment?
It caused the -60VDC bias to be about -30VDC. Hence red plating.
@Amp Amp: a tube without *negative* bias on the grid is like a wide-open valve; negative bias is like a throttle control or a "governor" on an engine, and prevents the tube from going full throttle and self-destructing (perhaps blowing a transformer as well). A leaky bias-supply filter cap shunts some of the bias voltage to ground, in this case lowering the negative bias by half. Or, if a positive voltage from the phase-invertor tube's plate(s) leaks through a bad coupling capacitor to the output tube grid(s), it will counteract and cancel some of the negative bias of the grid and lower the overall negative voltage (perhaps even sending the grid positive) causing the tube to conduct too hard.
@@goodun2974 Right. Sometimes the narrative can be confusing to some people. I was simply pointing out that the narrative could be confusing to some. I find this to be happening in some of the videos. It's always good to be clear for the entire audience. Thanks for your comment. I appreciate it.
Hey! I have an idea. Could you do a FAQ video? Just go through all the questions that come up often and answer them. That way you could refer your avid viewers to that particular video and, with a bit of luck, Avid Viewer will find what he is looking for. You do a LOT of videos so trying to find one kernel of information in a grain silo of kernels of information is a daunting task.. If I have a question, like, for example (hint, hint), "What brand of 6V6s do you recommend in a combo amp?", you could just say "Please refer to my highly informative and well thought-out FAQ video!" and all would be well in the world. I know you mentioned that particular topic in a video, but which one? I seem to remember you opined that 6V6 JJs in a combo amp weren't the best choice but I can't remember which tube you thought was a good choice (hint, hint). Oh, it would be such a time-saver if I could just remember which particular video had that particular bit of info in it (hint, hint).
It’s a good idea.
In the meantime, JJ 6V6s quickly go microphonic in a combo amp. EHs seem to be the best choices for 6V6s.
Until that changes.
@@PsionicAudio Thank you! Yes, I have JJs in mine and they've gone ridiculously microphonic.
@@PsionicAudio , as far as I am aware, TH-cam's search function doesn't allow us to search for a particular subject, or in this case a particular amp brand or model, *within just one particular channel's collection of videos*. If I'm wrong and there is a way to do this, please let us know.
Lyle , I would like to second his fine idea that you do a FAQ video , please. Please also cover good sources for parts and tubes , I’ve been taking notes but I’m sure I’ve missed some. Thx
Cheers Bebop
Dumb question: Does the damaged plug have an electrocution risk via the guitar?
Where are you located? Thanks
Loosing chassis grounding is never a good thing. Then all it takes is one leaky capacitor, or tube to electrocute you. There are too many bad things that can happen with a cord like that one.
@@qua7771 , also, a leaky "death cap" can be a shock hazard all the way up to the guitar strings if the amp doesn't have a grounded cord. Many guitarists are unaware that if the amplifier is wired right and has a good earth ground via the power cord, the polarity switch and/ or death cap are *unnecessary*. Occasionally, one also encounters an death amp with voltage leaking from the power transformer windings to the chassis, yet another reason why a grounded cord is a necessity..
Lyle is in Memphis TN.
@@goodun2974 I wouldn't play a vintage amp that wasn't modified to have those issues addressed. I'm not going out like that.
@@qua7771 , Ditto. I'm a tech, not a gigging musician, and any amp I work on gets a grounded cord and the death cap removed (and polarity switch disabled). No exceptions. A good safety test for the non- technically-inclined musician is to plug their vintage amp into a ground fault circuit interrupted (GFCI) outlet in the kitchen or bathroom, and flicking the polarity switch if the amp has one, to see if it trips the built-in breaker. If it does, you have a dangerous situation that needs to be addressed before you use the amplifier
Think I'm hearing what you meant about the TMDR v these amps when snapping the E or B string....?
The TMDR hasn't that ring or sustain...? Think the TMDR has that compressed...? Probably describing this inadequately 😉😎👍
The TM DR sounded like it had a badly set DynaComp built in. IMO.
@@PsionicAudio
It'll be interesting a few years from now when they come in for repairs, to see what you might be able to do to the TMDR once you get inside of them😉😎👍
I could change the ICE Module or resolder a bad pot/jack connection. Or swap a board if Fender makes them available to non-authorized service centers*. Other than that, they aren't "tweakable" - any more than I can change the innards of this laptop's CPU.
* I've been asked to be authorized service for a lot of companies but I decline. Not worth the paperwork, the second guessing, the lame pay, or the long payment cycle.
@@PsionicAudio
No fun in Mudville as far as the Tone Masters are concerned 😉😎👍
The future of tech is proving to be limiting indeed...?
No worries though..we have others and you to help us😎👍❤🖖
Goodevening....i have question.....i have a Fender Quad Reverb My Capacitor Mallory 25uf 25v has been damage what capacitor and what value of UF and value of Volts of the capacitor replace to the orginal capacitor( Mallory 25uf 25v)... Thank you Very much...
ALL the 25uF/25V caps should be charged out. They’re all 45 years old at least.
22uF or 25uf doesn’t matter, anywhere from 16V to 63V is fine. Sprague, Vishay, and MOD are all good choices.
Thank you Very Much to your advice...Godbless..
Whenever I see a wiring harness in these later CBS Fenders that have the white wire coiled like a spring around a bunch of other wires, I ask myself, how necessary was/is this, to presumably prevent oscillation or radiation of noise fields? Is it really that effective, or isn't there a better way to go about fixing the issues with the lead dress in these amps than that twisty mess? I mean, if it's effective, fine, I guess, but damn, it looks fugly! My mild OCD doesn't like it one bit.
I made an amp with very neat looking wiring, but it sounded horrible. It had all sorts of problems including ghost notes, frequency cancellations, muddy lows, and high frequency spikes caused by crosstalk oscillations. I had to tear down all the neat wiring, and do it over in a more electronically mindful way. That was a learning experience.
@@qua7771 , generally, running a bunch of closely-spaced wires together and/or bundling them together in a harness or loom is a recipe for noise and oscillation unless done very specifically so that the magnetic fields cancel each other out. I've never seen anybody else ask this question and publicly examine/discuss how and why the wiring was done this way in those later era Fenders. Next time I work on one I'll have to try and analyze which circuit paths are contained within that bundle.
If I recall correctly it was used as a type of shielding separating the b+. Wrapping it with the ground would help control noise even though it is a loose spiral.
@@goodun2974 Wires can become microphonic as well. It seems like an odd phenomena, but consider there are electromagnetic fields present. Tube amps have all sorts of strange anomalies.
More like having a 1959 Chevy 348 6 pack Impala SS with the original tires, brakes & hoses on it. Let's go for a ride! Let me update my life insurance policies first. I'll take that ride with the old oil. I can rent machine shop time & rebuild a motor, but I can't set my own broken bones.
Lyle, I gotta disagree with you. Red plating due to caps is caused by leakage, not high ESR. Leakage may not appear in the testers you used. (Leakage is parallel resistance, not series). High ESR means the cap isn't passing signal, or doing as good a job at filtering as it should (even if the capacitance value is correct). Sometimes leaky caps will show as higher capacitance as it takes longer to charge them. So caps that show unusually high are suspect. Either way, you definitely had an open cap, and that's enough reason to change both. I'm with you on the rest of the lecture.
Ah, but high ESR causes caps to generate heat which can cause/exacerbate cap failure. So an indirect cause of the failure but a correlated symptom.
If it makes you feel better, I’m not satisfied with how I presented that section. Was trying to show how a visibly good old cap could fail with serious consequences, but I didn’t want to get too in the weeds. I didn’t strike the right balance.
@@PsionicAudio What you say about ESR and heat is very true of filter caps in a switching power supply. That's what makes selecting the right cap for switchers important. I'm far less convinced that high ERS creates heat in audio signal coupling applications. Yes, a cap that "tests good" for value, can certainly be bad. To truly test a cap, you need to do at least ESR and leakage. Maybe value as well. Of course, if it's really leaky, it can be spotted with a live in-circuit test.
@@russellhltn1396 , I have seen plenty of domed, bulging-top caps in the lower-voltage power-supply and protection circuits of 1970's/80's solid state audio gear, which doesn't use switching supplies. If the cap in question isn't located near a hot resistor or regulator, then either it failed from ripple currents or just degraded over time and started generating internal heat as it transitioned from a "purely" capacitive device to one with ever-increasing current flow/voltage drop and the attendant internal heating. Also, sometimes the cap doesn't physically dome or bulge but the shrink-tube label will shrink back even though there's no hot components nearby. It's usually a sign of internal heating.
@@goodun2974 Oh, no doubt. I think you're trying to disagree with my comment on ESR causing heating in audio applications. But I think instead you've made a case for heating though leakage.
Reforming capacitors is a thing, but really, new caps are better.
people really criticised you for "noodling"??? 😂😂😂
so clueless hahaha
obviously gotta test the amps fairly extensively with a multitude of techniques as you've explained. there isn't time to play thru a set list of songs.
I know for a fact that you don't care either way but I actually enjoy listening to you doing tone tests.
seems like alot of tech guys are usually pretty decent players, I think that partially comes from always being around instruments and having expertise on finite details of how they work. it's probably a lot of fun playing different amps everyday after you fix them up. cheers 🍻
You kinda sound like Uncle Doug.
Maybe he sounds like me…
Not when Lyle actually plays, he doesn't! Or even when just noodling....🙂
Cap makers spec 7 years for peak useful life . After 7 years to 10 years non film cap fall off from the cliff . film caps do last longer LCR meter will clearly show that elec caps fall well out of spec after 7 to 10 years period . I hope people listen to your expert view of the real deal on these amps. Caps are not red wine they do not age well. Hater just keep hating as it is said here in the South . Your playing fills the bill for it use.
Are you saying they have a shelf life even if unused?
I would think that electrolytic filter caps would last substantially longer in an amp that rarely gets used, compared to one that is gigged out daily.
Secondly, spec sheets show the tested lifetime rating of various caps based on industry standards. I generally look for caps rated for over 10,000 hours, low ESR, and high ripple current.
This is the first I've heard of them having a 7 year life expectancy.
@@qua7771 From what I have read yes they have a shelf life for max performance.
I would rather your noodling, than some of the complete vanity player who drown out the amp, we need to hear amps breath.