1967 AB763 Bandmaster cap mods

[Chuck H]

THIS^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I always wondered why there is so very little blueprinting of exceptional sounding BF amps. Because the really great ones are chimey, but full and really seem to get under the note in that way that makes the amp seem intuitive to your playing, most are really just "aight" with workman like tone. You can usually find a sweet spot with any particular guitar, but nothing to say "Hey! Now I get what all the fuss is about!" Only about five percent of those amps have the mojo. And I, for one, would like to know what it is. It may be different in each case, but... Some drifted values and/or some lead dress difference, maybe even a wrong cap value installed so Fender could fill the order (that happened). Inquiring minds want to know.

I've been privy to two such amps. One was a BF clone built by a guy who claimed his amps captured THAT sound. They did and I was jealous as hell. The other was one you'd never suspect... A BF Bassman head. It was all stock, a little noisy, but it sang like a bird and growled like a lion. Big wet tone even without reverb, trem or the extra gain stage. I didn't have the opportunity to get inside either.

[J M Fahey]

Sometimes the difference is an incredibly "unimportant" error, which happens to be the right way.

John JR Frondelli who is a member here but doesnīt come often, works in a Tech Shop which is incredibly well situated in NY and rubs shoulders with the Gods on a daily basis.

Among others, U2 sends *all* of their stuff twice a year for maintenance, both for Tours or recording.
He had been intrigued by a certain revered and cherished small Fender amp (Harvard/PrincetonDeluxe?), **the** amp used by The Edge since forever.

He has half a dozen of them but he swears by that one and does not take it on tour for fear of losing it.
"None of the others sounds like that one"

So as part of his maintenance job he opened all 6 chassis on his workbench and compared them to find any difference.
As expected, basically the same (same schematic meaning same DNA) except for the cherished one: just repeating old information by heart, but apparently that one had, straight from factory, a .01uF cap where schematic asks for a .02 one.

Probably a Friday afternoon job, the assembler must have run out of .02uF ones in his/her parts tray and didnīt want to wait for more.

I suspect it was a coupling cap and the slightly reduced Bass made for aslightly cleaner distortion, so maybe usable somewhat louder for slightly improved "singing" or whatever.

Only noticeable by somebody who uses them every day and has 5 other ones to compare; Iīm certain nobody will pick it by ear and scream "million dollar sounding amp" !!!!!!

He was very careful NOT to "solve the error" by any means (Randall cough!! cough!! )

But then he runs:
https://www.dbmproaudio.com/

[Helmholtz]

Differencies in blackface combos are often due to different speakers.

[Leo_Gnardo]

Differencies in blackface combos are often due to different speakers.

As with any amp. Also the guitar, where the knobs are set, the player's technique etc. I've worked on amps that sound awful to me, but the owner plugs in and like magic, they sound terrific.

[Justin Thomas]

THIS^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I always wondered why there is so very little blueprinting of exceptional sounding BF amps. Because the really great ones are chimey, but full and really seem to get under the note in that way that makes the amp seem intuitive to your playing, most are really just "aight" with workman like tone....

The other was one you'd never suspect... A BF Bassman head. It was all stock, a little noisy, but it sang like a bird and growled like a lion. Big wet tone even without reverb, trem or the extra gain stage.

So... What particular BF Bassman? Could be any of 3 different circuits - quite different. At least the Bass channels are. Look at the AA864, AA165, & AB165. Most are either AA864 or AB165. Anyway, BF Bassmans all have 4 preamp tubes for a third "gain" stage on the Bass Channel. Look into it - especially the AB165. I've never tried lifting it, but that little tiny negative feedback loop might have something to do it... Also possibly the feedback on the 6L6s, though mine came without those (already removed). Mine also came with a Twin Reverb OT, so, fwiw.

As far as your description of BF amps in general, to me it sounds like you're describing most of the SF amps I've played, up to when they switched to the UL. There was a thread here years ago about "silverface amp pull" that was an interesting read, theorizing on why the SF had something that the BF don't. I guess we could look for the thread...

Justin

[Justin Thomas]

Juan,

It was a Harvard. I do remember that.
As for which cap, there's only 2 .02s to worry about, so I'll begin cloning that million-dollar amp (literally; it's gotten The Edge more than a few million) tonight!

Justin.

[Helmholtz]

As with any amp.

Sure, but what I meant was that Fender used a number of different speaker brands in the 60s and those amps are rarely compared at the same speakers.
I especially like the old 10 inch Oxfords.

BTW, the AA763 Vibroverb (which appeared first in 1964 as a single 15" combo) is identical to the AB763 Super Reverb except for the smaller size 8 Ohm OT (and speakers).

[Leo_Gnardo]

Sure, but what I meant was that Fender used a number of different speaker brands in the 60s and those amps are rarely compared at the same speakers.
I especially like the old 10 inch Oxfords.

BTW, the AA763 Vibroverb (which appeared first in 1964 as a single 15" combo) is identical to the AB763 Super Reverb except for the OT (and speakers).

Deafinitely true. At the time, if you grabbed whatever was in the store, or ordered up a new Fender, you might find Jensen, Goodmans, Oxford, Utah. For instance some years ago I worked on a bone stock very early Deluxe Reverb, chassis date stamped December 1963. Mellowest sounding Deluxe I ever heard! Double checked the circuitry, it was exactly as the schematic said. Only possible explanation, the speaker. Now I admit forgetting, but it was either Oxford or Goodmans.

Additionally, if the speaker failed, anything might find its way in there. A popular upgrade speaker at the time was the Jensen "Vibranto." Luv that speaker!

If I'm not mistook, the black Vibroverb and early Vibrolux are also identical to the Pro Reverb, except for an 8 ohm (A7A) transformer in the Vverb or 4 ohm (A6A) in the Vlux & Pro. Great amps, all of 'em.

[Helmholtz]

Deafinitely true. At the time, if you grabbed whatever was in the store, or ordered up a new Fender, you might find Jensen, Goodmans, Oxford, Utah. For instance some years ago I worked on a bone stock very early Deluxe Reverb, chassis date stamped December 1963. Mellowest sounding Deluxe I ever heard! Double checked the circuitry, it was exactly as the schematic said. Only possible explanation, the speaker. Now I admit forgetting, but it was either Oxford or Goodmans.

Additionally, if the speaker failed, anything might find its way in there. A popular upgrade speaker at the time was the Jensen "Vibranto." Luv that speaker!

If I'm not mistook, the black Vibroverb and early Vibrolux are also identical to the Pro Reverb, except for an 8 ohm (A7A) transformer in the Vverb or 4 ohm (A6A) in the Vlux & Pro. Great amps, all of 'em.

Are you sure about the Goodmans as they were UK made? Could be found in AC30s.
I know of Jensen, Oxford, Utah, C.T.S. (alnico and ceramic versions), Pyle and sometimes JBL. But there might have been more. Some of them even came in different (sounding) versions.


The Vibrolux had a smaller PT than Vibroverb and Super Reverb. All of them are great sounding amps.

[Leo_Gnardo]

Are you sure about the Goodmans as they were UK made? Could be found in AC30s.
I know of Jensen, Oxford, Utah, C.T.S. (alnico and ceramic versions), Pyle and sometimes JBL. But there might have been more. Some of them even came in different (sounding) versions.

Goodmans, yes. I can only guess at some time in the early 60's Jensen couldn't fill an order, then Leo and his crew had to punt to fill the demand for Fender amps, and landed on Goodmans. I was surprised as anybody what with having to import from England and all that. Can't let speakerless amps & cabs sit in the warehouse while you make excuses. Fill the orders & don't delay - or else our competition will eat us alive!

Somewhere around 1970, Utah became Pyle. Similar to CTS speaker changing to Eminence around that time.

One of my customers had the question, was the speaker outfit CTS the same company that made CTS potentiometers? Anybody know?

JBL, on special order. At some point mid 60's they painted the frames orange for Fender, and added the suffix "F" as in D120F. I've also seen a 70'ish Twin Reverb with orange-frame Cerwin Vega 12's, with Fender 'special design' labels stuck on. Orange paint = special design, I guess. Word was, that amp belonged to Paul Butterfield at one time.

Sometime in the early 70's, Radio Shack offered speakers intended for guitar. With orange painted frames! I guess they figured guitarists would associate the color with high quality speakers. (Insert laugh track here.) They weren't awful, but they weren't too great either. Chalk it up to marketing...

[Justin Thomas]

Wait, CTS speakers became Eminence? No wonder I've never had a complaint anout any CTS speaker in an amp, as long as said speaker wasn't blown...

Justin

[Chuck H]

So... What particular BF Bassman? Could be any of 3 different circuits - quite different. At least the Bass channels are. Look at the AA864, AA165, & AB165. Most are either AA864 or AB165. Anyway, BF Bassmans all have 4 preamp tubes for a third "gain" stage on the Bass Channel. Look into it - especially the AB165. I've never tried lifting it, but that little tiny negative feedback loop might have something to do it... Also possibly the feedback on the 6L6s, though mine came without those (already removed). Mine also came with a Twin Reverb OT, so, fwiw.

As far as your description of BF amps in general, to me it sounds like you're describing most of the SF amps I've played, up to when they switched to the UL. There was a thread here years ago about "silverface amp pull" that was an interesting read, theorizing on why the SF had something that the BF don't. I guess we could look for the thread...

Justin

Unfortunately I never even looked into that. It was a sort of "Hey, you like tube amps. Check this out." And I was handed a guitar cord. I don't even know what speakers were in the cabinet. Which is a good point made by the Helmholtz and Leo discussion. And you're right, there's a mix stage for the channels, so three gain stages (if you can call unity a gain stage). So nothing at all definitive here. What I DO know is that nearly every other BF amp I've plugged into left me a little flat. Which is confusing because you do hear THAT tone often enough to know it's real. I have modded some BF amps and gotten close to that tone. I analyze tracks I hear on the radio whenever I can tell it's a bf topography amp (though it's impossible to know just WHAT bf topography amp it might be) and sometimes you can tell that the amp is mediocre, but the player is outstanding (re: Sultans of Swing. Which I think was a silver face SR?). There's a lot of that. Once in a while you'll here an amp that is really on point. The frequency curve is right and it's grabbing notes in a way that implies compression, but isn't, because it's still dynamic. And sometimes that's in the hands of an otherwise mediocre player. I've trained myself to hear through the difference between playing and amp tone... I must have! Otherwise I could never plug into an amp and know it was special because I'm not a special player.

[Justin Thomas]

Hence mike6158's quote in your sig?


Jusrin