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In Reply to: RE: Fender Bassman - PS & Tone posted by Triode_Kingdom on August 09, 2016 at 06:10:28
Most ppl used the Bassman for guitar use (not bass use). Blues-wise the four 10-inch dual 5U4GA, 5E6 or 5E6A circuit --- tweed combo is the ultimate Bassman. Using 12AY7 inputs and 12AX7 phase splitter. Lots of voltage sag, that you can actually hear --- when played at volume. Plenty of harmonic interactions between the four 10-inch speakers. Open back. Many Tweed Bassman had Jensen P10R or P10Q speakers. Arguably the best 10-inch alnico of the tweed-blackface era.The output tubes were 6L6GA. Many had Sylvania gray glass loaded into the amp. Combination of tubes used, speakers used, and circuit type = a very sweet tone.
I'm used to the blackface era head units. The AA864 is considered the ultimate blackface. Least amount of crazy circuitry and feedback. Bias control pot. The AA165 is next. But, very hard to find. I believe in early 1965, Fender went to the oft criticized AB165 circuit. With it's balance pot on the output. And local FB on the 6L6GC tubes. The BF and SF all have solid-state rectification.
The blackface or modded silverface head unit sitting on top of a 2 or 4 X 12inch cab is the way to go for lead guitar use. I have a DIY 2 x 12 inch cab with Weber Alnico 12A150 and Celestion Vintage 30 ceramic loaded in a sealed enclosure. Very efficient. Great bass, even with the 40 watt Bassman head unit. Will post photos.
Tone Lizard has an nice site on the various Bassman circuits and mods to get later blackface and silverface head units back to the earlier AA864 topology. Including the polarity issue with certain global feedback schemes.
For Bass use, the Bassman is barely adequate, even in small gigs. Esp if the lead guitarist is using a 40+ watt Fender or Marshall combo. Forget it. Just go for a Showman reverb head or even bigger Ampeg, Soldano, SUNN, etc head unit. And big, enclosed 12-inch loaded cabs.
Boy! I LOVE this topic. Many ppl have been guided through the various mods to get to tonal nirvana... on Fender Amp boards.
8^)
Edits: 08/09/16 08/09/16 08/09/16Follow Ups:
The AA864 is considered the ultimate blackface. Least amount of crazy circuitry and feedback. Bias control pot. The AA165 is next.> >
I got the impression the 5F6A was the best circuit, and the best for a new build? My impressions playing through different input tubes was that I preferred the sound of 12AX7s all through. I got the most sustain that way. Using lower mu tubes tended to decrease the sustain, which I found less attractive. I play a fretless.
5F6A is during tweed era. AA165 is first blackface era. 5F6A have the most DIY and clone kits available. It has single GZ34 replacing the two 5U4GA rectifiers. And runs 5881 output tubes. Both 5E6A & 5F6A still has 12AY7 input tubes.Just my personal opinion. I like the 12AY7 input/6L6GA era Bassman better. And most ppl that have played both like using LEAD guitars through the earlier 5E6-A. Think that dual 5U4GA really gives the amp a unique character, which is kinda lost with the GZ34. Some ppl pull one 5U4GA to get even more sag.
The tone of the 5E6A is further from the later blackface AA165. So maybe, that is why I like it better. With 20/20 hindsight --- more difference between the two.
8^)
Edits: 08/09/16 08/09/16 08/09/16
nt
nada aqui
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Buy Chinese. Bury freedom.
Circuit modded back to AA165:
Edits: 08/09/16 08/09/16
Late 1950s Tweed Bassman 5E6A with 1957 Telecaster.
nt
That's interesting, I was thinking the 5U4s would produce the most PS sag and maybe the best tone. I didn't want to bias the question though by mentioning that. So... the guitar amp I'm planning to eventually build should probably be different than the prototype power stage I designed a few months back. As it stands, it's a very clean amp with EL34s and a stiff solid-state supply. Maybe I should add a 5V filament transformer and a pair of 5U4s. That would result in a much softer supply. This is totally contrary to amplifier design for hi-fi. Is it reasonable to simply copy the original 5E6A schematic as a first-time build? Will the EL34s degrade the tone? My OPT is low-Z, about 4K, so it matches those better than the 6L6 family.
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Buy Chinese. Bury freedom.
FWIW, I think you will get closer to 6L6 sound by employing either KT77s or "fat bottle" 6CA7s. Those 2, like the 6L6, are beam power tetrodes, even if they are "electrically equivalent" to the true 3 grid pentode EL34.
Eli D.
Yeah, the dual 5U4GA was part of the incentive for Jim Marshall's early 40 watt EL34 and KT-66 amps. He decided on the GZ34 rectifier (as it was actually CHEAPER in UK, compared to imported 5U4G or -GBs).
Stiff PSU is ok. You just need to adapt to it, with playing style (pick attack, heaviness of pick, etc). The sustain is more dramatic with solid-state. But, tube rectifiers kinda have this "breathing" quality. Where you hear the notes fade and come back. Like a singer's voice, trying to hold a note.
For smaller gigs or just having fun with friends --- I find the tube rectified, 10-25 watt amp the best. One that you can crank up and get some nice overtones, without blowing yourself out the window. And causing the neighbors to call the cops.
A nice amp to model your DIY after might be the Matchless Chieftain. AWESOME amp! Plenty of juice when you need it. But, also good at lower volumes.
The big question is this: Do you like the tone of the Chieftan? It does have more features than the Bassman. I already have a reverb tank and driver transformer ready to go. Also, I have parts to build a true vibrato (like Magnatone) that could plug into the effects loop. On the other hand, I wouldn't want to sacrifice tone for either of those. With a little more work, those effects could be configured to plug in between the guitar and the amp.
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Buy Chinese. Bury freedom.
Edits: 08/09/16
I like the 12AY7 input, dual 5U4GA Bassman. Quite unique tone. Chieftain has a bit more modern tone. Maybe, due to Matchless use of Mills resistors in the circuit. And Jupiter style coupling caps.
Guess it depends out what product you are after. The coke bottle tube Fender tweeds have a unique tone, that is a big part of a lot of famous recordings. Hard to duplicate that tone with pedals and fingers.
I think those 1940-50s 6L6GA tubes are under-rated. Warmer mids than the later 6L6GC. Kinda mix of a good 6V6GT and 6L6GC.
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