what is the cause of channel imbalance in my preamp?

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I have a preamp with one 12AX7 at each channel in cathode follower circuit. Right output is ~20% lower than left output with the same input signal. This phenomenon is not tube- or grid choke-, or cathode choke(3 below)-dependent because switching between the right and left produced no change in the pattern of imbalance (still ~20% difference).
1) cathode bias resistor (shared for the two triode in one 12ax7) 470 ohm (equivalent to 940ohm when only one triode section is used)(rt -1.422v, lt=-1.322v why different????)
2) a grid choke 640H (DCR RT 19.7k, Lt 19.5k)
3) a choke between bias resistor and ground (DCR Rt 10.4k, 31.4VDC; LT 11.1k,31.1vdc)
4) B+ = Rt,240VDC ; LT,242VDC (shared but 2V difference)
5) input capacitor = 1 uF, output capacitor = 8 uF
Could anybody guess what is causing higher current through the right tube and deepen the bias voltage? I have no device to check capacitors. At least the 4 capacitors are not shorted. Can some abnormal capacitors reduce signal level?
I would appreciate your help.

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Topic - what is the cause of channel imbalance in my preamp? - yhm23280@gmail.com 22:29:44 03/10/07 (2)

Who made the preamp? - Russ57 04:37:31 03/11/07 (1)

Re: Who made the preamp? it was due to.... - yhm23280@gmail.com 06:21:26 03/11/07 (0)

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