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Hammond organ pwr supply? What would this support?

crispycircuit

crispycircuit

Super Member
I have a stand-alone large pwr supply from Hammond organ. H-AO-71-1 and was hoping I could find the specs? Anybody have any knowledge of this. My searches come up empty, Maybe someone used one for a build. It's heavy and looks impressive. I have some outputs ready to go. It could be fun
 
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Power-wise it should run a lot of things, the hitch gets into voltage distribution. Its two HV supplies at different voltages, so its a little more complex to use for a stereo amp. With some fiddling you could probably get two supplies at close enough to the same voltage to make it an effective twin mono rig though. Easy way would be to take the hotter of the supplies and put a zener diode at whatever that voltage difference is between the center tap and ground. You'd end up with matching voltages from B+ to ground, and the zener would take up the difference without adding a bunch of extra resistance to the circuit. The different resistance in the windings would probably make the voltages not track perfectly side to side but it may be close enough to not be a problem.

but accounting for that you should be good for a pair of channels at ~25 watts each. It wouldn't quite exactly be twin mono. HV supplies would be split, but you'd be sharing heater and bias. Slightly weird but if you have to share things, those will affect it the least.
 
Yep, it's the wrong PT for that. Might be a good choice if you find a second one. That would extract everything possible from those outputs.

Jack
 
depends what exactly you want to build. If you want to do something a little off the beaten path and have a lot of tubes, push-pull-parallel EL84 should work into a load pretty close to what A470 transformers present. IIRC those are 3.4k primary, PPP EL84 by the book would be about a 4k. Not a perfect match, but not such a gross mismatch that it couldn't work.
 
Maybe it's just me, but the idea of eight EL84s in one stereo amp is a little daunting. I've weighed the pros and cons of this approach in the past, mainly because I have dozens of NOS 6V6 and 6W6 variants that could be used. In the end, I've always come back to the simplicity and lower replacement cost using a pair of EL34 for a low-Z match. In this case, I also don't see how the PT could be used for two identical channels of PPP at 35W/ch.

Jack
 
I own one PPP amp, and it was built that way at the factory. I've never really been motivated to build one for exactly the same reasons you haven't been. The dollars per watt equation also tends to get bad when you go with parallel tubes vs a single tube that would get to approximately the same end result.


another random thought, build more or less what Hammond built with it. Stereo EL84 plus a single channel bass amp thats about double the power. 3 channel amps aren't exactly the easiest thing to make use of though so you'd probably need fairly specific use conditions for that to make any sense at all.
 
I was thinking about that too (great minds think alike). You could even include an onboard crossover system in the front end, and I would build the three amps on a separate chassis like Hammond did. Anyway, the OP dashed the idea with those A470s. His best choice for a more conventional build is probably to buy a suitable PT and save this one for the future or sell it.

Jack
 
TriodeLuvr said:
Maybe it's just me, but the idea of eight EL84s in one stereo amp is a little daunting. I've weighed the pros and cons of this approach in the past, mainly because I have dozens of NOS 6V6 and 6W6 variants that could be used. In the end, I've always come back to the simplicity and lower replacement cost using a pair of EL34 for a low-Z match. In this case, I also don't see how the PT could be used for two identical channels of PPP at 35W/ch.

Jack
Click to expand...

This worked quite well:

index.php


https://audiokarma.org/forums/index...amplifier-now-were-playing-with-power.798989/

There's no reason why someone couldn't do something similar with the Dyna A-470 outputs. The only caveat, is that greater care may need to be taken, to avoid oscillation between the parallel output tubes. But, that's been done quite well in the past- the Eico HF30 is one example.

If I did this- I would run the Dyna A470 transformers in pentode mode- just don't use the UL taps. The EL84 needs different tap placement percentage (IIRC, 25% as opposed to 43%?) than EL34s. Pentode mode will give more power on the lower B+ used by the EL84, though... that will make up most of the power difference due to the lower B+.

In my case- each transformer was about 9K, into a pair of EL84s. A Dyna A-470 would be effectively 8.6K into each tube, if four EL84s are used in PPP, per transformer. So, you should get about the same power I got- about 35w/ch.

The point about the Hammond power supply not quite being optimal for this, is spot on, though. You could make one PPP EL84 channel, but that lower voltage power supply section isn't strong enough for two channels of PPP EL84...

Regards,
Gordon.
 
That's a fine looking amp Gordon! I just read the thread for the first time. It's not clear to me how the output transformers are connected. Did you parallel the primaries and secondaries both, or only the secondaries?

Jack
 
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