Hammond amp into rocket or express???

[chrisc]

Hey Everyone,

I bought a hammond AO-29 amp a while back for next to nothing and its just been sitting. I figure its time to use it for something.

It uses 6V6's in push pull with fixed bias. The schematic shows the PT putting out 305v after the 5u4gb. It has a few 7 pin pentodes and single triodes I'd love to use someday.

So the question is what next? a 6V6 express or a 6V6 rocket? I've built a rocket and I love it, no buts its perfect. If I do another rocket, I want to incorporate at least one of those pentodes into a second blendable channel. I might do a clubman sort of channel or just do a simple stripped down pentode. Dont know yet.

If I do the express, I have a NOS stash of those old yellow astron caps laying around that I would love to use. Would they be good in this circuit, or should I save them for something else?


Thanks
Chris

[RJ Guitars]

Chris,

Do I understand correctly that you have 305 volts DC after the 5U4gb rectifier tube? My thought is that with a GZ34 you could get voltages close to the Rocket specifications. Normster created a 6V6 Rocket years back and apparently the results were superb... I have not built one for myself but it is a tempting idea. Rockets are pretty friendly toward layout and component swaps.

That available voltage may be a bit low for a typical 6V6 Express although I wouldn't let that deter you if you are up for a more challenging build.

Looking forward to some photos and a progress report.

rj

[M Fowler]

Structo posted this layout after he made one.

Mark

[Structo]

Be careful with that Hammond supply.
It's a bit misleading because of the way they wire the B+.

On my amp it had 380v on the high voltage winding which came to about 720v after the 5U4.

I had to use a Zener to bring the B+ down.

Hammond used a lot of tubes to load down the PT.
It also uses the field coil for the speaker as a choke which also brings the voltage down.

[chrisc]

Thanks for the replies and layout.

And thanks for the heads up on the PT. I'll have to get a zener diode to bring that down then.

Did you just use a zener, or the mosfet amplified version? What size did you use?

Chris