Failed LTSpice Simulation of HK Citation II

[gadget73]

thats still assuming the transformer is actually symmetrical. It may need an asymmetrical feed to compensate. Really sort of need the actual amplifier in front of you to confirm that.

 

[TriodeLuvr]

... equal plate load resistors and no potentiometer. Signal is symmetric.

The output of a a long tail pair with a resistor in the tail will NOT be symmetrical if the plate load resistors are equal. If you have removed all the feedback loops from the simulation, the output of the LTP should be unbalanced.

Jack

 

[rustnrot]

I have a Cit II. I connected about 3 other OPTs into the circuit to see how they performed. In no case did the replacements perform as well as the original. I made no adjustments to the original circuit and in every case I had a balanced output, suggesting the original output transformers are indeed symmetrical.

 

[gadget73]

the output won't really be unbalanced, you'll just see some extra 2nd harmonic content if it doesn't cancel perfectly. If the grid signal is not symmetrical, and the output does not have 2nd harmonic content, that kind of implies the transformer is not perfectly symmetrical and it wants that uneven grid drive to make it all come out right.

'course we're assuming the grid signal is not in fact even. A scope to ground on each output tube grid will answer that question. If the input is even in the unit but the sim says its not, the sim is wrong.

 

[S=j*2*pi*f]

Take the transformer out of the sym, or replace with something ideal. The output of a LTP phase splitter with a resistor for the tail will have unequal output amplitudes with equal plate loads. This is due to a common mode signal at the cathode that is about 1/2 the differential input signal. When the cathodes are biased with a current source, the amplitudes become equal.