6L6 Carmen Ghia ?

[topbrent]

I have a nice Carmen Ghia Clone.  I really dig the simplicity of the amp.  It's tone control is very effective.
Fun amp to play, but I would like to experiment with a louder version someday.

I have had the thought of building a 6L6 or EL-34 version of this amp.

Is there anything that jumps out from the schematic other than power tube voltage that would need to be addressed in the PI and power section for a 6L6 build?

Would the PI need any attention to drive the big octals properly.

Thanks for any tips.

[phsyconoodler]

The schematic you have is for EL84's.With 6L6's you need more plate voltage,a totally different PI and different cathode resistor/cap and of course much larger screen resistors.
  Take a look at a cathode biased Fender amp like an early tweed Super.
www.schematicheaven.com

[FYL]

I would like to experiment with a louder version someday.

A 6L6 or EL34 version would give maybe +2dB.

Is there anything that jumps out from the schematic other than power tube voltage that would need to be addressed in the PI and power section for a 6L6 build?

An EL84 AB1 PP needs around 30 volts (peak) to be fully overdriven, I'd say roughly 60V for EL34's and maybe 90V for 6L6GC's... So you basically keep V1 and redesign a whole new amp after it.

[tommytornado]

So.... is that the tone control used in the CG?

[topbrent]

So.... is that the tone control used in the CG?

Yes.

[jojokeo]

What kind of pi is that and how does it work?

[topbrent]

The Dr. Z carmen ghia is a modified hammond AO-35 reverb amplifier that was used in A-100 and M-100 organs from 59-61'ish

Dr.Z tweaked a few values for guitar friendly use and it is a fun little amp.

Early style, Hammond AO-35 amp based original Dr.Z Carmen Ghia.


Hammond AO-35 original schematic

[darkbluemurder]

What kind of pi is that and how does it work?

I believe it is a fixed bias phase inverter - at least that is what I heard - but I have no clue how it works.

[jojokeo]

Is that picture actually one of Dr Z's first CGs? (actually using the Hammond amp)

That's interesting about the pi as I'm not familiar w/ that kind of design. On my laptop from work & remembering his circuit it appears that he did use a lot of Hammond's values and circuit as there's a lot similarity. Thanks

[PRR]

The PI is like a Fender Longtail.

Fender used self-bias to raise the grids to a significantly positive voltage. Hammond just gets a +24V source and nails the grids there. By itself, insignificant. But there is also a +42V source, divided to +12V, feeding the cathode, with a strap 9-8 in the divider. If the 9-8 strap were broken, the cathodes would rise _far_ above grid voltage, cut-off the driver. This may be how the reverb could be muted remotely without exposing signal-leads to interference.

[jojokeo]

The PI is like a Fender Longtail.
 This may be how the reverb could be muted remotely without exposing signal-leads to interference.

After viewing 2 CG schems, there's actually a lot of component changes from the orig. Hammond schem in the first two stages. But, the pi and power sections appear to have been kept intact for the most part.

Thanks for that info PRR. Regarding the pi being like the LT - Since they're using the 33k on the cathode, if the pi were changed to the more traditional LTpair layout, I'm guessing that using a 820r to the cathodes and leaving the 33k as the tail would be good in place of the original?

[drew]

Does anyone by any chance have a gut-shot of one of the original CG's that used the Hammond chassis?