I've been digging and digging for his comments about this issue and haven't retreived it yet but in the process I came across Crowhurst's article about cathodynes and he mentioned what I now believe I read of Hafler's comments, in that issue of the different high FR plate/cathode. And so now I believe he was describing the additional short FB circuit from 6CA7 screen to driver that Dynaco added to the ST-70 to compensate for the HF response to add more stability to the amp. It wasn't about normal signal levels being out of balance. I may keep digging for that but I think it's moot at this stage. All enjoy the ride.
20to20,
and Rayma,
1. Dyna Stereo 70 . . .
The negative feedback capacitor that connects from the 'Pull' screen and its UL tap, to the cathode of the input tube.
It does not have Lagging phase shift at high frequencies, helps the stability.
On the other hand, the global negative feedback that takes signal from he output transformer secondary, does have a Lagging phase shift at high frequencies. It includes the inductive leakage reactance from primary to secondary (yes Lagging).
These are all interesting facts above, but they have nothing to do with the signal amplitude balance of the two concertina cathodyne stage.
2. Please do not let anybody criticize the cathode-coupled phase inverter, that uses a CCS (constant current Sink for the cathodes).
With proper design, it has signal amplitudes that are Intrinsically Balanced throughout the audio frequency range.
I only have one balanced signal source, a Magnavox CD player with L and a R balanced XLR outputs.
It is the only way I can use my balanced amplifiers.
For all my other of my push pull amplifiers, I use the cathode-coupled phase splitter with Constant Current Sink for the direct connected cathodes.
. . . Oh, yes, I still have one self inverting push pull amplifier; the phase inversion takes place in the output stage, a CCS (Sink) for the direct connected cathodes).
and Rayma,
1. Dyna Stereo 70 . . .
The negative feedback capacitor that connects from the 'Pull' screen and its UL tap, to the cathode of the input tube.
It does not have Lagging phase shift at high frequencies, helps the stability.
On the other hand, the global negative feedback that takes signal from he output transformer secondary, does have a Lagging phase shift at high frequencies. It includes the inductive leakage reactance from primary to secondary (yes Lagging).
These are all interesting facts above, but they have nothing to do with the signal amplitude balance of the two concertina cathodyne stage.
2. Please do not let anybody criticize the cathode-coupled phase inverter, that uses a CCS (constant current Sink for the cathodes).
With proper design, it has signal amplitudes that are Intrinsically Balanced throughout the audio frequency range.
I only have one balanced signal source, a Magnavox CD player with L and a R balanced XLR outputs.
It is the only way I can use my balanced amplifiers.
For all my other of my push pull amplifiers, I use the cathode-coupled phase splitter with Constant Current Sink for the direct connected cathodes.
. . . Oh, yes, I still have one self inverting push pull amplifier; the phase inversion takes place in the output stage, a CCS (Sink) for the direct connected cathodes).
You can enhance a little the stage splitting R6 into two parts more or less equal in value, and bootstrapping the midpoint from the cathode of the phase splitter with a large capacitor, say, a 4.7uF @ 250V. This adds positive feedback but in a quantity not sufficient to make it to oscillate. This gives you an extra gain you can use to further cancell out with nfb if desired. Also linearity is enhance as dynamic plate loading value tends to very high value.