Hammond organ reverb amp/6GW8 tube question?

gearhound

gearhound

Lunatic Member
An old friend just parted out an old working Hammond organ.
He GAVE me....what appears to be the reverb amp....from the organ.
Pretty good condition and nice iron.
The tubes are: one 6CA4 rectifier tube, and a pair of 6GW8 tubes.
What is a 6GW8 tube....and what kind of output could I expect....from what appears to be a PP tube arrangement?

Steve
 
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It's a combination triode/pentode tube.

The output power rating was somewhere around 4 watts for that tube.

EDIT: Is it an H-AO-44 amp???

. . Falcon
 
Yes it is.............H-AO-44 amp.
Is it capable of being a mono audio amp?
Or is this amp a better candidate for a guitar conversion?
Thanks!

Steve
 
The 6GW8 puts out about 80% of an EL84, i.e. the class A output rating is around 4 watts but is closer to 13.5 watts in AB push-pull.
 
Think 6aq5 with half a 12ax7 in the same bottle. Nice little tube if you're building a single-end pentode amp and want to conserve on the number of tubes. You can wire the triode's output right into the pentode to get 2 stages in one socket. You could do P-P easy enough too if you put the phase splitter ahead of it.
 
I'm starting to scrounge up new caps and resistors for this amp.
I have some NOS Sprague Vitamin Q's that will work.
I also some NOS Allen Bradley carbon resistors to use.
I just ordered a JJ 40x20x20x20 cap can from Tube Depot.
The balls starting to roll........................

Steve
 
It's pretty easy to convert to a PP power amp.

I have one of those... I just deleted all the solid-state limiter/compressor circuitry at the input... and made a more conventional circuit to the input of the first small-signal tube (the triode section of the 6GW8 closest to the input jack). IIRC, I put a 470K to ground on the input jack itself, then a .022uf cap from the input jack to a convenient terminal on the terminal strip there, then another 470K to ground there, then from there, a 47K to the grid pin of the triode section. Very much like the input of a Magnavox AMP175, in effect.

That, and recapping the amp (I replaced all the ceramic caps with film caps, replaced the cathode bypass cap on the output tubes, and increased the power supply capacitance about 50% most everywhere) was about all it took. Sounds great. Very gutsy little 10w amp!
 
I can handle a soldering iron just fine.....but redesigning a tube amp is WAY out of my league.
My tube amp experience is strictly.....replace old part with newer part of same value.
I can work from a schematic IF it's a pretty straight-forward design.

Steve
 
Gearhound. Look at it this way. This project might get you to the next level. Learning isn't all that hard if you really want it. (I built 2 airplanes, now I know how!)
 
GordonW:

Probably a dumb question.....but I gotta ask?

Do you know what pin number is the grid pin to the triode section?

Thanks!!
Steve
 
GordonW:

Any chance you could show me on a schematic.....the changes you made?
Any help would be greatly appreciated!

Thanks!!
Steve
 
I'll have to draw one up. Kinda just went off the cuff, and did it. :D

May take a while... but I'll try to get it done...

BTW: the input pin I was referring to above... it's pin 1.

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Regards.
Gordon.
 

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Thank you Gordon.....the help IS appreciated!!

BTW: I have a line on another H-AO-44 amp....local and cheap.
Tube mono blocks.....wouldn't that be sweet!?

Steve
 
gearhound said:
Thank you Gordon.....the help IS appreciated!!

BTW: I have a line on another H-AO-44 amp....local and cheap.
Tube mono blocks.....wouldn't that be sweet!?

Steve
Click to expand...

I'd do it in a heartbeat. If I can find another A044, you can believe I will!

Regards,
Gordon.
 
GordonW:

Picked up that Hammond-AO-44 an hour ago this morning.
5 minutes from my house.
Works perfect.....no hum whatsoever.
He wanted $40.....but took $30.
I have enough caps and resistors to do one amp.....but not two.
Gonna check out Justradio (Canada).
I bought capacitors from them when I recapped that yard sale 1969 Webster TP-12-1 mono PA tube amp.

Steve
 
I ended up removed the transformers from both Hammond-AO-44 organ reverb amps.
I got from a neighbor, a beautiful NIB black crinkle steel chassis with cage.
I mounted the power and out[put transformers on the chassis in, what will be, a dual mono 6gw8 P-P design.
Now....it's NOT the biggest chassis in the world.....so a dual mono design.....WILL be a tight fit.
I have two JJ 40x20x20x20 e-cans that will NOT fit on the already crowded chassis top.
I'm thinking of either.....mounting them on the BACK of the chassis.....or.....abandoning them altogether.....for individual caps mounted UNDER the chassis?
I'm also considering making this a dual mono integrated amp.....as I have two mono 100K ladder-type stepped attenuators, gathering dust in a drawer?
Either way.....now that I have FINALLY gotten off my butt, and started the project.....it's really started to look like something substantial.

Will wonders never cease??

Steve
 
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