Looking for Hammond organ schematics
- Thread starter grindfix
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crispycircuit
Super Member
Usually the amps are inked stamped . Numbers like AO-35,AO-29,AO-43....That the number your looking for....Lets us know what you have?
One from E-100 is AO-63 (H-AO63-1) Unit is complete with power cord. I haven't powered it up.
One from H-100 does not have AO number anywhere. it has 126-000050 number. H-100 power supply transformer was removed by someone before me and power cord was cut.
There is also AO-69 preamp that came from E-100 as well.
All units are full of tubes.
Can any of this be used/re-purposed for stereo setup?
Thanks,
Dmitriy
crispycircuit
Super Member
The AO-63 is 2 amps on one chassis. One amp uses 7591 tubes for outputs (larger output transformer) and the other uses 6bq5 tubes (small output transformer). You could use it for stereo. All tho they would have different output power. The H-100 amp? I would need a pic of the chassis to see what you got.....I have converted many Hammond amps into audio/stereo amps,You need a matching pair for stereo. They sound very good. Got any pics?
The smaller transformers are the outputs. Looks like a pair of 6bq5. Not sure but those might be the same ones I have on my Madison-Fielding amp. Also looks like 7591, so 3 channel I suppose? If that large transformer matches tthe 7591 transformer on your other chassis, what I'd personally do is move it and end up with a stereo 6bq5 amp and a stereo 7591 amp.
Yes, both amps are 7591 but transformers aren't same.
Is there a transformer spec sheet to make sure power transformer has enough power for both 7591 channels?
Especially filament power.
Thanks
The 3 channel amp surely would have enough power to handle it.
The 7591/6bq5 amp it would depend on how many tubes its currently running and if it has a power feed to other places. I wouldn't be too surprised if either the heater winding went to a connector, or if it had an extra heater winding just for that purpose.
The 7591/6bq5 amp it would depend on how many tubes its currently running and if it has a power feed to other places. I wouldn't be too surprised if either the heater winding went to a connector, or if it had an extra heater winding just for that purpose.
3 channel amp has remote power supply with power transformer missing.
2 channel one has connections for preamp unit so you are probably right.
It should have enough filament supply for another channel. I'll be on the lookout for matching OPT.
So, my guess is transformers, tube sockets, tubes are getting reused and circuit gets new components, correct?
What would new circuit be based off?
2 channel one has connections for preamp unit so you are probably right.
It should have enough filament supply for another channel. I'll be on the lookout for matching OPT.
So, my guess is transformers, tube sockets, tubes are getting reused and circuit gets new components, correct?
What would new circuit be based off?
You'd have to see what the original circuit was to see if it is or isn't appropriate to clone. If not, a Fisher or Sherwood receiver with 7591 or 7868 tubes would work as a good starting point. You'll have to get the feedback proper for those specific transformers though. Have a look at the original Hammond circuit to see if it has any frequency limiting going on. You may need to include it, or a tweaked version of it for stability depending on how the transformers act.
Ditto the EL84 transformers. You've got your pick of circuits to base it around, but the feedback has to be tuned for the specific transformers in use. I found that the HF response of mine were not amazing, so I had to do some frequency limiting that was actually not too different than the original Hammond circuit to keep it stable. Without any tuning it wanted to oscillate and be generally stupid. It also didn' want a large amount of feedback for the same reason.
Ditto the EL84 transformers. You've got your pick of circuits to base it around, but the feedback has to be tuned for the specific transformers in use. I found that the HF response of mine were not amazing, so I had to do some frequency limiting that was actually not too different than the original Hammond circuit to keep it stable. Without any tuning it wanted to oscillate and be generally stupid. It also didn' want a large amount of feedback for the same reason.
E-100 organ AO-63 amp update.
Powered up with variac with all 3 original speakers connected. 6gw8 channel started to crackle at about 80v.
I turned it of and flipped amp to inspect.
One of the resistors on 4 section can burned up. So I pulled rectifier tube for that channel and eventually all tubes from that channel. But main amp is GOOD! I wired one of the RCA jacks directly to amp input(10k resistor on pin 5 of 7247 tube) I went through all 7247 tubes I had to only find one that works!
Lucky because I'd condemned circuit fault otherwise. I'm not impressed with the gain but it might still be very weak 7247 PI tube.
Will OPT handle the gain if 7247 is replaced with 12AX7? Of course circuit will have to be modified for that but it could be borrowed from Dave G's modified Fisher 400. 7868 and 7591 are same tubes with different base, correct?
GE 7591 power tubes that amp came with are running very hot and pulling too much current at given bias voltage making me back off variac to the point where distortion is too obvious. Installed original Hammond 7591s that were in the H100 amp and was able to balance bias much better but I think circuit could benefit from individual bias adjustment mod IBAM that many of you know.
Here are voltages
Variac 112.6v
Bias -19.15v
Pin 5 .58v (spec .4v)
But the bottom line is that this OPT is capable of producing decent sound and circuit does not appear to cut frequencies much if any.
I will run some frequency tests with audio generator tomorrow to see how good/bad my hearing is!
Powered up with variac with all 3 original speakers connected. 6gw8 channel started to crackle at about 80v.
I turned it of and flipped amp to inspect.
One of the resistors on 4 section can burned up. So I pulled rectifier tube for that channel and eventually all tubes from that channel. But main amp is GOOD! I wired one of the RCA jacks directly to amp input(10k resistor on pin 5 of 7247 tube) I went through all 7247 tubes I had to only find one that works!
Lucky because I'd condemned circuit fault otherwise. I'm not impressed with the gain but it might still be very weak 7247 PI tube.
Will OPT handle the gain if 7247 is replaced with 12AX7? Of course circuit will have to be modified for that but it could be borrowed from Dave G's modified Fisher 400. 7868 and 7591 are same tubes with different base, correct?
GE 7591 power tubes that amp came with are running very hot and pulling too much current at given bias voltage making me back off variac to the point where distortion is too obvious. Installed original Hammond 7591s that were in the H100 amp and was able to balance bias much better but I think circuit could benefit from individual bias adjustment mod IBAM that many of you know.
Here are voltages
Variac 112.6v
Bias -19.15v
Pin 5 .58v (spec .4v)
But the bottom line is that this OPT is capable of producing decent sound and circuit does not appear to cut frequencies much if any.
I will run some frequency tests with audio generator tomorrow to see how good/bad my hearing is!
You probably won't get a load more gain out of a 12ax7 honestly. Depending how they wired it, the high gain section may already be the voltage amp. The phase inverter side will have no gain no matter what you do.
7868/7591 effectively the same other than the base, yes.
7868/7591 effectively the same other than the base, yes.
