CFollowers direct coupled into output grids?

[Guitarist]

I found this design and was wondering if maybe some element of the design is usable for a guitar amp. An odd B+ for C-1 (bias) and C-2 , looks clever though.

[Rob Mercure]

Nothing is unusual in the design and there have been guitar amps that have incorporated all of the elements 'cept that strange "standby" feature with then neon light (I assume that is the purpose of the feature). Ray is our "AB2 guru" and may have more specific comments - I could probably respond to more specific questions if you have such.

Rob

[Ray Ivers]

Do you know the manufacturer of this amp? It looks somewhat similar to a Fisher design I've seen... I wouldn't be surprised if it would make a pretty good guitar amp as-is, maybe revoiced with the addition of some Ck's... and of course that 1M resistor at the very top would have to go... ;)

It looks pretty cool to me - extensive direct-coupling (hence the C-2 voltage), AC balancing, lots of gain; I think the 150K Rk on the Schmitt stage may be a schematic error, though.

Ray

[Arthur B.]

Do you know the manufacturer of this amp? It looks somewhat similar to a Fisher design I've seen... I wouldn't be surprised if it would make a pretty good guitar amp as-is, maybe revoiced with the addition of some Ck's... and of course that 1M resistor at the very top would have to go... ;)


Do you mean to say that the 1M resistor should be removed, leaving a direc connection, or (more likely) that the feedback loop inculding the 1 M resistor, should be removed?


It looks pretty cool to me - extensive direct-coupling (hence the C-2 voltage), AC balancing, lots of gain; I think the 150K Rk on the Schmitt stage may be a schematic error, though.

Ray

I don't think it's a schematic error. Mullard style phase inverters are supposed to be like that.

[Guitarist]

I found the design At http://www.triodeel.com/schindex.htm but the the amp is a homebrew model listed down aways. It's interesting how some of those amps have a PI then a driver prior to the output tubes. I was weaned on having those both in one tube like most guitar amps are.

[Ray Ivers]

Ah, a homebrew - that explains that freezing-cold-biased Schmitt splitter (800uA per side!). A 12AX7 would have been fine there; looks like they may have copied the ECC83-based direct-coupled Schmitt PI used in both the 10W and 20W Mullard designs, and increased the values for use with a 12AT7 when they should have decreased them (the 10W/20W amps use pentode input stages, too). It's a cool, simple design, and an excellent platform to tweak from IMO.

Ray