@terry9
I would use a dual trace scope, make sure the two channels have identical gain, use one emitter resistor on channel 1, call that the reference. Then use channel 2 to see how the others (one at a time) match up at various power levels. I would find the results interesting.
Have you also looked at the output transistor current driving the speaker at high levels, high frequencies? Trumpet music, thats a killer? Have you measured the impedance of the primary side over frequency? I have found some stepups have so much capacitance that more of the energy goes into the transformer than the panels. FYI, the 57 and 63 transformers, though different, are very cleverly wound. A torroid typically has lots of shunt capacitance that you have to drive. The QUAD transformer does not.
BTW, I am not impressed at all with the Plitron audio transformers. Van Der Veen’s paper seemes flawed to me. He is a great speaker promoting his idea of automatic bias. He believes you can use a gapless tube output transformer to make a practical amplifier. I take great issue with that. I think there are some unasked thus unanswered questions. I would ask him, "what happens when there is a DC offest in the output stage. It will happen when the amp is pushed?"
Similarly if you have any DC across your primary the core flux will be off center. I cant say how many mV is ok, but i think at 50 it could be noticed and at 100 mV it might be a real problem.
Here’s how to set up your test:
Scope ground goes to hot output terminal of course. Im assuming the output stage is emitter follower.
Dont forget to float the AC power on your scope. Othewise you will be shorting your output.
On my bench I only have one piece grounded. Everything else floats. Even my soldering iron floats because sometimes I solder amplifiers while they are on. There are parts of the circuit that dont much mind. Dont do that with SS amps, the are unforgiving.
I would use a dual trace scope, make sure the two channels have identical gain, use one emitter resistor on channel 1, call that the reference. Then use channel 2 to see how the others (one at a time) match up at various power levels. I would find the results interesting.
Have you also looked at the output transistor current driving the speaker at high levels, high frequencies? Trumpet music, thats a killer? Have you measured the impedance of the primary side over frequency? I have found some stepups have so much capacitance that more of the energy goes into the transformer than the panels. FYI, the 57 and 63 transformers, though different, are very cleverly wound. A torroid typically has lots of shunt capacitance that you have to drive. The QUAD transformer does not.
BTW, I am not impressed at all with the Plitron audio transformers. Van Der Veen’s paper seemes flawed to me. He is a great speaker promoting his idea of automatic bias. He believes you can use a gapless tube output transformer to make a practical amplifier. I take great issue with that. I think there are some unasked thus unanswered questions. I would ask him, "what happens when there is a DC offest in the output stage. It will happen when the amp is pushed?"
Similarly if you have any DC across your primary the core flux will be off center. I cant say how many mV is ok, but i think at 50 it could be noticed and at 100 mV it might be a real problem.
Here’s how to set up your test:
Scope ground goes to hot output terminal of course. Im assuming the output stage is emitter follower.
Dont forget to float the AC power on your scope. Othewise you will be shorting your output.
On my bench I only have one piece grounded. Everything else floats. Even my soldering iron floats because sometimes I solder amplifiers while they are on. There are parts of the circuit that dont much mind. Dont do that with SS amps, the are unforgiving.