Hello,
I have an old Hammond organ amp, AO-68 that I gutted and built a PP 6L6 guitar amp. The original power tubes were 7591 and the output transformer is what I am wondering about...
The secondaries are black, green and yellow. It appears that the stock setup had the yellow tap grounded and the other two going to the speaker socket.
Is this normal? When I first tried it out it was very distorted and low power. (when I bought it, it supposedly worked, and had weird, extra added wiring in places that was not recognizable)
I grounded the black wire and used the green one on my output jack. It sounds really good, and correct now. But I don't know what impedances are with the green and or yellow taps. Any ideas?
Also, anyone know if the yellow tap being grounded is normal or maybe an error?
Thanks,
Daniel
I have an old Hammond organ amp, AO-68 that I gutted and built a PP 6L6 guitar amp. The original power tubes were 7591 and the output transformer is what I am wondering about...
The secondaries are black, green and yellow. It appears that the stock setup had the yellow tap grounded and the other two going to the speaker socket.
Is this normal? When I first tried it out it was very distorted and low power. (when I bought it, it supposedly worked, and had weird, extra added wiring in places that was not recognizable)
I grounded the black wire and used the green one on my output jack. It sounds really good, and correct now. But I don't know what impedances are with the green and or yellow taps. Any ideas?
Also, anyone know if the yellow tap being grounded is normal or maybe an error?
Thanks,
Daniel
here is a schematic...
That's what I thought wrt to the colors. The power stage is the like the bassman, and the feedback is variable to adjust for amount you want back into the phase inverter. I have both fixed and cathode bias on a switch.
The voltages on the schematic are from another amp and was the targets. The only ones on that page that are correct are the ones on the power supply, plate and screen voltages.
In cathode bias it is really off, so I have only been trying to get it working in fixed so far.
**ignore the -50v in the bias part, it was a target also...
That's what I thought wrt to the colors. The power stage is the like the bassman, and the feedback is variable to adjust for amount you want back into the phase inverter. I have both fixed and cathode bias on a switch.
The voltages on the schematic are from another amp and was the targets. The only ones on that page that are correct are the ones on the power supply, plate and screen voltages.
In cathode bias it is really off, so I have only been trying to get it working in fixed so far.
**ignore the -50v in the bias part, it was a target also...
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Well I'm not sure what the problem was, but I do have the current running 'balanced' in the tubes now. With my adjustment pot I get from 51mA to 19mA which is exactly where I want it. The plate voltage is about 460v so that 51mA is right on the edge.
I increased the cathode resistor to 440 ohm and that works great. I have about 40v on the cathode pin.
The only thing that's strange is the speaker taps. The yellow seems to be 4 ohm. The amp really sounds bad, buzzes weirdly on the front of the picking when I'm using that one through an 8 ohm speaker. I switched to the green tap and the clarity is much better, louder and does not buzz.
Thanks for all the input.
I increased the cathode resistor to 440 ohm and that works great. I have about 40v on the cathode pin.
The only thing that's strange is the speaker taps. The yellow seems to be 4 ohm. The amp really sounds bad, buzzes weirdly on the front of the picking when I'm using that one through an 8 ohm speaker. I switched to the green tap and the clarity is much better, louder and does not buzz.
Thanks for all the input.
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