EPIC Guitar Amp Conversion - Complete Tube Amp Redesign
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- เผยแพร่เมื่อ 17 ต.ค. 2020
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In this video, we'll follow an EPIC guitar amp conversion of a 1940 Knight 35 Watt Tube PA Amplifier. This conversion stretched over the course of months and got set aside for various reasons, but it's finally finished. The main features of this amp are the push-pull 6L6G output with transformer phase inverter driven by a 6F6, and a cool and unusual Type 83 rectifier tube which contains mercury vapor. When it came to me, it had all the original tubes, but the wiring was DREADFUL, and ended up needing much more work than I had anticipated. In fact, this one would end up requiring an almost complete redesign and rebuild. I would borrow 6SJ7 preamp ideas from a 1950s Fender Tweed Champ and a 1950s Gibson GA75.
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NOTE: As some have pointed out, the demo portion left a lot to be desired, and I agree. I didn't bother dragging out my mixer and mics on this one and used the internal mic on the Sony camera, which I'm finding out is passable for speech and some low volume music and sounds, but can tend to emphasize mids and certain unpleasant frequencies too much, especially in LOUD amps like this one. I'll probably film another demo of this thing properly and put it on Channel 2, because it really does sound fantastic in person, I just gotta capture it better..
What a unique circuit and amp.Great sounds , after all that work. Bet you have got at least 30 hrs.in it. That's $2,250 if you charge just for labor,not including parts . Wow,but look at what your getting ,one off custom built amp. If you look at small 20 watt amps like the Friedman Amo there priced at $1499 or so. So your getting a higher watt amp at reasonable price.Good work if you can get it . Have a great week.🎸👍
Great looking and sounding amp. Very creative rework! What happened with the overheating feedback resistor?
is the Sony camera the root cause of the sketchy audio at the start of the video too? The voice audio sounds clipped but not all the time, could be a repair video maybe?
Don't the Mercury Vapor tubes emit x-rays?
Wow. Sounds great despite the mic clipping and over loads. Would love to hear a better recording. That amp sounds like it could be quite the amazing little beast.
Dude.... Brad..... I'm sure almost all of us know how Fugazi this project is.
No worries, take your time. We appreciate you letting us watch.
Thanks.
Thanks for understanding.
@ moonboogie N8 - I'm curious about "Fugazi" here. It can mean "effed up," can be (New York or New Jersey) Italian for "fake," and it also means "messed up." I'm guessing "messed up" here due to the original design? Thumbs up!
@@bobvines00 its fubar
@@michaelcandido2824 fixed up beyond all recognition 😆 no joke, i had a DBA registered as that a few years ago back and i still get mail addressed to FUBAR remodeling
Brad, as a fellow technician, my hat's off to you for redesigning and salvaging this old amplifier. You did a very impressive job, and that particular unit is something that I wouldn't have wanted to attempt. Your engineering skills are very impressive and imaginative, and I admire your neat and tidy soldering and wiring. I've watched many of your repairs and refurbishing videos, and it is refreshing to see the talent that you have for working on old school electronics. I'm old school, I'm 60 years old, and my initial (Army) electronics training was heavily vacuum tube oriented, so I love working with on the old stuff and seeing you work on it too. Many thanks for always showing us the schematics, it's fun to follow along! I've converted several of these types of relics into guitar amplifiers, but none have been as messy as the one that you shared here, great job man!
There is one thing that I do differently though, I've always clipped the terminals on the ash can capacitors and left them in place for aesthetic authenticity. Antique electronics is my passion and I try to leave a set looking as original as possible.
Hey man, I almost can't keep up with all of this new content. Rock on!
Omg you just made my weekend, so glad you decided to do this.
Hello Brad! : Those two little button cells you took out most likely put out about 1 volt maybe 1.5 volt on a real good day at REAL LOW CURRENT!! they most likely were used to POWER the CARBON button style microphones of the time!! these style microphones actually need a slight voltage supplied to them to operate! these mic units actually had a small metallic button that contained carbon granules that were acted upon by a small metallic diaphram just like the old style telephone of the 1920's to 1935 or so have a good day!!
Awesome! That's really cool that back then they had a sort of "phantom power" of that type for mics that need it.
I researched an amp that I have ... and those things were called "bias cells". They actually existed to provide bias for the grids of preamp stages.
Don't know if this will work but here is a "forum snippet" that discusses it..... www.antiqueradios.com/forums/viewtopic.php?t=122629
@@robertruth3281 Hello Robert: Yes they did provide bias for grid biased stages !In case of this amp though you will take notice that the bias is supplied by means of the cathode, so this bias cell could be there to
provide the very slight voltage and current to a carbon button mic element as carbon button microphones were used primarily on P.A. amps up to the late 1930,s and in military operations well into the 1940's and beyond because of the carbon buttons ability to shrug off physical and electrical shocks like EMP events. They were robust!
@@johnbellas490 thank you for that John. It adds to my knowledge base!
That amp has a unique sound... very nice Brad, One of your better videos to date... Thanks
Well cool man, patience and dexterity in abundance and a bog load of skill. Very enjoyable 🙂
Never seen you do that before very nice work that was a hell of a cleanup
Sounds great! Great job brother
Hello Sir, I am one of many of your extremely happy subscribers and wanted to tell you of how Incredibly Professional you are of your work. You're an Awesome Dude! I will continue to watch your Great work and Content! Please do not allow them negative trolls get on your nerves. Please take care and keep up your Awesome work! Many thumbs up!
So nice of you
Thanks for all the inspiration Brad you and Doug are helping me get this all happening and having a lot of fun learning to build amps.
Very interesting deep dive into an amp from yesteryear. You took us along for the ride. In the time it took to do that restoration, you could have built and amp from scratch. Much respect to your love for the early designs, and your teaching style. This is not easy work that you do. So much to learn.
Thank you for sharing the journey.
Loved your redesign and I'd like to say you are an artist to be able to draw a schematic like you do. You made it fit exactly on one page of your graph paper. Everything is in perfect proportion. Amazing.
Beautiful job Brad, but I wouldn't expect anything else man.
Thanks Ron.
@@TheGuitologist Great work. I remember in the beginning of the video you had said the cost and time of the build far outweighs what you were compensated and it was no longer worth taking in outside work. I for one would love to see more work like this. If your going to custom design an amp from scratch essentially from a pile of old parts shouldn't you charge for it? I think so. Your providing a Botique service, a Botique amp build. I would imagine charging someone around $1800 for this build plus parts would be reasonable. They may not want to pay that but there would be justification for this charge. With all your research before you even pick up a soldering Iron.
@@@chrislangdell117 Absolutely agree Chris. I thought $1000 but yeah! Brad deserves it. The guy should ask Brad nicely if he would sign it for him & put a guitologist sticker on it!
excellent find! that's a killer conversion job!
Great video brad as usual we all appreciate the time you put in to let us look over your shoulder
Great job Brad!
Good to see you back on the tools
Another cool video! You're on fire!
Bad ass project man can't wait to see it work
Another fantastic video Brad. You are right up there with Uncle Doug when you do work like this and I know you consider him to be a real renaissance man. I thourghly enjoyed this, Thanks and best wishes.
Super cool amp. Uncle Doug said you need to add a swampy tremolo circuit and hook it up to that meter.
The meter is hooked up to the output. It actually works, I just didn't film it working.
Dedicated and skilled - a deadly combination. Despite not having a clue about 99% of what you did here, I can still admire the effort and the result. Nice one!
Sounds great!
nice job
I was born in Plainfield NJ (home of The Beaver capacitors). Never heard of the company while I lived there but asked my father this morning and found out my grandmother worked there during WWII making capacitors. Thanks for a great family laugh.
What a great result. Lifts the soul
That amp is so sweet!
Like seeing you take on something big. It's inspiring.
THIS is the killer content!
Nice Beaver!
Thanks, I just had it stuffed.
@@TheGuitologist Who knew that dry Beavers from the 1940's still worked so well...
Brad that amp is insain . One of the best sounds I've heard so far .. that head is a true jewel to have .it just rings like a bell . Wow man !!!
Nicely done.
Love it Brad. Thanks!
Excellent video. Nice meter. Great night light. You must add a small meter circuit. Seeing that bounce would be Awesome!
Thanks.
Absolutely Correct! That would be the icing on the cake for sure.
The meter works perfectly. Bounces with the guitar. I just got lazy and didn't film any b-roll of the bounce while playing. I was rushing to finish the video and get it published and forgot to do that.
Sweet sounding amp!!!
That is bad assed Brad. Really sound sweet to my ears.
That was really interesting especially allowing us to here the thought process in figuring the schematic to make it sing! Amazing!
And a few words about these mercury vapor rec tubes....they need to be preheated... If not their is a chance that they can explode, when a recombined mercury blob is sitting on a anode when applying the high voltage... The whole fluidly mercury need to be down at the cathode area only the vaporized mercury can form an electric path between anode and cathode. Usually the MV tube datasheet inform you about pre heat time and handling of the tube itself. I have several amps in allmost daily usage which use AX50 (like dual 866a in one envelope) MV rectifiers... They need about 10mins pre heat. The operation manual of one of these amps says: pre heat the Amp at ot least for 5 mins before service. If the Amp was in storage or in transit pre heat at least one hour in order to not blow up your Rectifier Tubes.
The first thought I got from the sound of the amp was George Thorogood’s House Rent Blues. Great break up that screams the blues. Great video Brad!
This is a master class on tube amps!!! wow!
Brad, you're an artisan and an archeologist in your own right. Digging through these broken and shattered cathedrals of sound and eventually rebuilding those towards a new glory.
Sounds amazing
WELCOME BACK BRAD 🎩🕶
This is the old Brad we know and want to see. Hope all your problems solved or will solve soon. Keep on posting videos like this! Great guitarplay also. Greetings from Germany
sweet build Brad always inspiring and informative. wish you could do more your build of the bogan pa amp inspired me to try that conversion now i have done several thanks for the inspiration keep those videos coming
Brad, wonderful job! That thing is a Beast dripping with evil goodness!
Good job Brad! Time to go out and break some stuff after that epic struggle!
Great job bro!
Hey Mike! Thanks, mate. Cheers!
Dude....soooo cooool!
Absolutely Incredible Madman...
I fell asleep a ways in and woke up to the playing at the end. Now that is a good sounding amp.
these 89$ from 1940 would be $1,654.64 in 2020 money
and damn, i need this amp for my rehearsal space which is located in a german world war 2 bunker
@Dagwood Dogwood Great place to record "Sounds of the Apocalypse"
@Dagwood Dogwood yes man, my room is right at the starirway (it is an above ground bunker) 3rd floor. insane reverb chamber. i will definatly upload a video on that soon
i will be waiting on that reverb video. the one you already uploaded is pretty nice and interesting too. keep it going, nice channel :)
@@martindisslertation8882 thanks man, appreciate you checked out my channel :)
Brad, these projects are a labor of love. Like Uncle Doug's steam punk projects. This amp looks beautiful. and great unique tone. Thank you for the great content, this along with a cigar and a couple whisky shots is my therapy during this China Virus pandemic. ((;
That's gotta be one of the coolest looking (now) guitar amps to exist
Wooo this amp looks and sounds so fkn great plus the secret sause in the power rectifier
wow, nice, thanks for sharing!
Sweet Thanks Brad
Damn that sounds awesome!
Man what a project on this one Brad. Always fun to follow along with ya on these. btw, you reminded me of the time being the Peruvian village of Los Frijoles Perdidos and listening to the Howling Monks of Monte Tonto. Good times man.
I bet that was amazing.
Fantastic.
Love your videos along with Uncle Doug!! The 83 rectifier is very interesting. Was used in some of the very first Fender amps...The Woody, I believe. They quickly moved to the more familiar 5U4 and ditched the mercury vapor rectifier. Now, if you crank the volume on a tube amp, the output tubes ask for more current. The tube rectifier typically has "sag" and cannot quite deal with the sudden current demand....so the voltage drops and you get compression. With an 83 rectifier, greater current demand causes more of the mercury vapor to conduct and vaporize. As a result, the voltage does not sag when the power amp current demand increases. You get much less rectifier compression. The 83 behaves more like Silicon Diode rectifiers! Pretty neat!!
Nice description. Is that why this amp has a crisper attack? It was very 'out front' with each string pluck.
@@sski Yes, definitely! The attack will be fast and crisp with an 83 tube. The tube requires a special base socket....4 pin socket...to go along with its other unique characteristics.
@@TubeGuy1975 Excellent! Thank you for the verification. :D
This I did not know. Thanks for the insight!
BEST Film Yet, a full length feature!
Glad you dug this one. It was a ton of work making it.
I love the meter !
Hey man, people don’t understand how much work research..it takes. Brad.great job
Yes, those caps may still “work” but the 50 to 100% drift indicates the plates have physically moved closer to each other. In electrolytic capacitors, the electrolyte has dried out and will not survive the original voltage rating.
You really need a high voltage cap tester to be sure, and those aren’t cheap. Mr. Carlsons Lab has an amazing vintage unit with a magic eye that I would kill for!
I have a couple vintage cap testers. They need service though and I just haven’t gotten around to it yet.
@@TheGuitologist You are a fucking hot mess jesus fucking christ. lmao
@@matthewf1979 You're absolutely right. Brad needs to get his other cap testers going. Mr. Carlsons lab also has a cap leakage tester that is to die for, that I can't seem to get any build info on.
@@nevillegoddard4966 That cap tester schematic and BOM is available from Mr Carlson's Patreon. I think it's still $1 to get access to it.
The quirky "one of a kind" looks, all it's bells and whistles, and of course the sound make this amp fawkin' coo-ell as hell. I want one of them!
Killer! Can't wait to break into the old Silvertone that a friend found at an estate sale. It pretty much needs the same treatment this beast got.
I appreciate and admireyour dedication to preserving as much as you could. I recently found a series filament style stereo amplifier, a pair of 50L6 GT's and 7025's. It was basically laying outside in the Florida weather, only shielded from the rain by an old RV. The dirt and god knows what else was so thick inside the chassis you could barely see the chassis and tube sockets inside. It was just the amplifier itself, no name or indication what it came from. On top of that it looked like it had experienced a catastrophic failure at some point and had been hacked with bad repairs and all kinds of stuff was disconnected, like someone had attempted to fix it not knowing what they were doing and simply chucked it outside. I had no schematic and no hope of tracing what was there and restoring it so sadly i jusy had to gut it and save what i could. I'd like to make something of it that at least cosmetically resembles what it once was, maybe find a way to use the same compliment of tubes although that might be more effort than its worth. It's a bit of a ship of Theseus situation but even if it could be restored it'd be the same i suppose due to how bad off it was. I'd like to try to take inspiration from weird and unique old amps like Ampeg's, Valco, Sunn, things like that. Not just a fender or Marshall copy or something thats common and just sounds like everything else as you mentioned. Apologies for the long winded comment, i appreciate your content so much. I've learned a massive amount from your channel and you inspired me to learn to fix things myself when most people my age just throw it away and buy the newest thing. Thank you sir 🙏
I see why you passed on my Operadio PA conversion now lol. Awesome work.
Brad, Wow! This was an involved project. I understand why you don't want to take any more customer jobs like this, but maybe you'll do some like this for yourself? Thank you for finishing this video and sharing it with us!
And thank you for a _long_ detailed video -- I've got more time to watch videos like these now, but even if I couldn't take this time all at once, I'd _definitely_ keep it open in a tab to return to as I had time!
It sound realy good great video have a good day
Very nice deep dive into what it takes to do a custom like this killer! If you do one again, do an auction with min bid. Put your brand on it and see what happens. You might be surprised.
"Gee whiz Ward! You were a little hard on the Beaver last night."
Keep em glowing!
This will be a classic...
Nice Job, as always, Brad! The Brown Beaver Cap's ESR was 0.15 kOhms! So this thing sure was leaky as hell.
just letting you know, you know, this was a cool vid you know, and everything like that.
Hi Brad - so I noticed that this amp has coke bottle tubes in it. I also noticed that you had quite a few boxes of new tubes on the bench and some used tubes on the bench that caught my eye. I noticed you had some used PFPTT tubes (Pink Floyd Psychadelic Tone Tubes), which are also known generically as "prescription bottle tubes with built in safety caps". Pink Floyd really knew how to make use of these tubes to create some serious psychedelic tones. ;-)
That amp sounds awesome! I seem to hear a hint of a natural brown tone.
Good Job converting the 70 volt public address amp. The odd jack was to mute the background music when making announcements. The announcement microphones were probably telephone type handsets.
Sounds good wish I knew how to do that kind of work.
You have excelled yourself, B. Thank you, once again. I'll try soon to send you a wee something from my State Pension ... But please never forget ... I, like you, will forever be *Twenny-One!* Stay free. R 🎯
"When you don't know what the fuck you're doin' " Brad learns and teaches.
Thanx man
Dude! This project may have been a pain in the tookus, but the end result is friggin’ awesome! As your daughter would say, “Tone for dayz!” 😲😎🎸🎼🎶🎵
just discovered your channel on YT.., l like your style ., you're not full of shit , you hand deliver it with no postage due and I dig that refreshingly...., thanks
Amazing amp. I prefer the first channel. I agree with you this is something different very rich in harmonic. You should post a more Hifi of this demo not everybody are ready to listen a 1.25h amp video like me haha. Sound killer. Keep rocking!
Good day Brad. Had a thought regarding the stuck knob on the pot, have you tried Kroil brand penetrating oil. This stuff can really get into every nook. Just a thought, it works wonders on stuck nuts/bolts in mechanical work and can be used very sparingly if you allow it time to creep down into whatever you've applied it to. I'm a lifelong mechanic/welder and have little knowledge or skills with electronics and I must say you've really opened my eyes to the subject. I love the conversions, and I almost pulled the trigger on a Laffiette pa amplifier I saw on eBay and a free Hammond organ I saw on craigslist. I imagine one day soon I'll give it a go, and hopefully don't blow it up. Take care dude, love the channel.
The end result was very cool sounding. I now expect to see Marshall add that stool design to their lifestyle brand.
Paper/film hybrid caps are one thing which almost never go bad. These capacitors were developed by Sprague and originally sold under the trademark "Di-Film" but are more commonly found as Pyramid "IMP" or the Ajax "Moulded" capacitors which were used in a lot of '50s/'60s guitar amps.
that last little lead run,damned that was sweet maybe at 1:23 or slightly after
Goodvid
It looks and sounds good now that it's done, but the "before" views make me think that this was the kind of rig that Leo Fender looked at and said "this is awful, I know I can do better than that".
And of course, he did. Your layouts and lead dress look great, and even though the sound quality is less than stellar, I can tell that it sounds mighty good.
Definitely one of a kind.
Looks like you did it again......Nice!
Hi , new to this chat arena but been a huge fan of you Brad. You always take the time to explain the assessment all the way to the result , anyway.
I will be getting a Vikings 50 - 96 receiver by Eaton's circa 1948. Just the chassis and all components and I was told it was working when removed from the cabinet.
Just wanted to know if it's too much for a first attempt project.
I have one of those component testers, what I did for test leads is I made a pair of banana jack sockets connected to pins, so I can just plug in standard multimeter probes, tweezer probes or clip leads. I was gonna try fit them into the case but I don't know if that'll work too well.
When I repair shit and I price up it almost always goes way beyond the price given and sometimes I get asked how comes it's tool so long! Then when I say I've not charged you the extra 10-15 hours of labor at £45 an hour I always get a oh I see! But we do it because we love to do it. Great job brother
I think I had rather start from scratch than rebuild a project like this.
To get the knob off you could have used a needle tip bottle to feed the back side of the knob some rubbing alcohol, that is how I remove lots of different adhesives I have even undone probably five bottles worth of krazy glue (not really that much but a good bit that was on a guitar pick guard's controls... just sharing some tactics my dude. You do great work and I like your commentary.
This is the second amp I've seen using a 6SA7 pentagrid converter in one of it's stages. That's a very strange tube to use in an amplifier. It's basically two pentodes stacked on top of one another with one plate and cathode. It was designed to replace two tubes in superheterodyne radio receivers and improve the performance at the same time. In the usual application the bottom set of grids are used as an oscillator which directly modulates the electron beam coming off of the cathode, and the top set of grids acts as a mixer, mixing an input signal with the output of the oscillator before the resulting signal is taken off at the plate.
Try using 'mixer resistors' from the wipers of those two volume pots. You'll get less interaction. Basically the same way that many Fender and Marshall amps use a 270k-470k resistor in series with the volume pot wiper, which then join together to 'mix' the signals.
Did good on this one it rings ..
i would gut it start again
Sweet!!!!