Bassman AA568 unused triode applications

[evil79]

Just wondering what people have used the unused triode in bassmans for. Looking for some interesting ideas.

[Chuck H]

I have to admit that I've never been inside one... But on the schematic I don't see an odd number that disposes the dual triodes in use. Four preamp tubes. Two 7025's a 12ax7 and a 12at7. All triodes accounted for. Maybe you're thinking of a different model?

http://tubeamplifierparts.com/schema..._schematic.gif

[evil79]

No, the aa864, ab165, aa568, and probably a couple more leave the first triode of v2 unused. Check it out.

[Justin Thomas]

Chuck, in all Bassmans with 4 preamp tubes from AA864 onward, there's an unused half-tube, or a single triode, left dangling for anything. I believe it's V2 that only uses one half the tube. In the AA864 & AA165, there are three stages in the Bass channel and 2 in the Normal. In the AB165 and through the rest of the run, there are two stages in each channel and a 3rd stage shared in common. Still a half a triode left.

So, you could make V2 parallel... add a switchable distortotron stage... any way to put in tremolo with 1/2 a tube?

Justin

D'oh, simul-post...

[evil79]

Chuck, in all Bassmans with 4 preamp tubes from AA864 onward, there's an unused half-tube, or a single triode, left dangling for anything. I believe it's V2 that only uses one half the tube. In the AA864 & AA165, there are three stages in the Bass channel and 2 in the Normal. In the AB165 and through the rest of the run, there are two stages in each channel and a 3rd stage shared in common. Still a half a triode left.

So, you could make V2 parallel... add a switchable distortotron stage... any way to put in tremolo with 1/2 a tube?

Justin

D'oh, simul-post...

I thought about tremolo, like in a Princeton reverb. But then you need a speed and intensity pot...

[Chuck H]

Well... I posted a schematic that proves otherwise. But... That doesn't mean that Fender themselves didn't put the wrong model sheet on an amp. It's not that unusual actually. As you can see in the aa568 schematic I posted, all triodes are accounted for. In order to have an unused triode there would need to be two triodes unaccounted for!?!

Your amp must be one of those odd cases. I'll look up the model number prior and following the aa568. Perhaps one has an unused triode. And that would be your actual amp.

[Justin Thomas]

This is a Bassman... trust me, it's there!
Stoohpid Fender multi-purpose model numbers! AB763 can be anything from a Deluxe Reverb to a Twin Reverb...

Justin

Edit: I think the thread TITLE should say AC568 Bassman, not AA568 Bassman, which doesn't exist...

[The Dude]

Chuck, that's an AC568 not AA. Not to worry, I made the same mistake.
I don't find an AA568? Is there such thing?

[evil79]

This is a Bassman... trust me, it's there!
Stoohpid Fender multi-purpose model numbers! AB763 can be anything from a Deluxe Reverb to a Twin Reverb...

Justin

Just look at the inside of any of these bassmans and you'll see. They all have a triode unused. And it's not ab763 I'm talking about. No bassman has an ab763 circuit. And I'm only talking about half of a 12ax7.

[Justin Thomas]

I used AB763 as the most common example. As shown in the scheme above, the AC568 can also be a Bandmaster or Twin Reverb or Dual Showman.

And my "trust me..." was to Chuck and Dude, since they put up AC568 Bandmaster scheme and not a Bassman. No fear - I love Bassman heads & know well what's in there.

Justin

[The Dude]

......Edit: I think the thread TITLE should say AC568 Bassman, not AA568 Bassman, which doesn't exist...

In that case, Chuck linked the correct schematic. I don't see an unused triode there?

[Justin Thomas]

This work?
http://rudn.nodevice.com/preview/big/365/365856-1.jpg

Justin

[The Dude]

There we go!

[Chuck H]

Hmmm..!?!

They are both AC568 schematics!?!

Let's assume that Justin's schem is accurate then I'm well aware of the unused triode in many Bassman models. I just didn't find this in the initial schematic search. THANK YOU FENDER! Ok... So, working from the schem that Justin posted...

There's the option of stacking it in front as an overdrive OR putting it just behind the PI as a stage to be overdriven. the former will generate a more modern overdrive, but never quite reach the modern uber gain thing. The latter should probably create a more bluesy, but saturated clipping. Similar to, but perhaps not as refined as the *umble type sound. This is probably the one I would opt for as I think the amp is suited to it more than metal. This, of course, depends on the players musical styling.

OTOH... These Bassmans have a great tone on their own. The extra triode could be used to buffer an effects loop! Or add another tube and use it as a mixer stage for a reverb!?! It really depends on the musical style of the player. What's your poison?

[Justin Thomas]

They are both AC568 schematics!?! ... OTOH... These Bassmans have a great tone on their own. The extra triode could be used to buffer an effects loop! Or add another tube and use it as a mixer stage for a reverb!?! It really depends on the musical style of the player. What's your poison?

Yeah, this is why Enzo is always saying, please post the NAME of the amp, and not just the AA763 or 6G11 or such. Especially with the BF/SF amps. Same model NUMBER can be 5 radically different amps.

Honestly, set up right as-is, these are plenty gainy and bluesy IF you're willing to put up with the volume. They don't need much more than a pedal out front if you really need more gain. But Neil Young and beyond is possible. First recommendation is trimming the bass out if you wanna run it that loud, to dodge the Fender Fart. So before delving into Major Modland, give it a very thorough run as is, and wind it up past 6 if you're bold. Because my personal opinion is to use it for something that does nothing to the raw basic character of the amp. But, it's yours, so...

Justin