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Citation II one channel dead!

75.56.159.163

Posted by needhelp on February 3, 2007 at 12:34:59

History of Amp

About two years ago I upgraded all the caps and diodes in the power supply using values suggested by Jim McShane on his website. I also replaced 4.7mf. .22mf and .47mf caps on the circuit boards. The amp has been working fine as an every day player for the last two years.

One day I was playing the amp with no issues. Turned off the amp after playing about ½ hour and replaced all the 12by7a tubes and turned the amp back on. After that time one channel has been completely dead quiet. No pops, his or hum. The other channel is working fine.

I rolled all the 12by7a’s and the 6550’s and the same channel is still out. Put the old tubes back in same issue.

I measured some voltages and the V1 12BY7A has about 60 volts on pins 1,3,9 where it should have 5.3v. The plate is also over 300 where it should be about 170.

I check resistances on r1,r,2,r3,r4,5 and all same within bounds. I checked resistances comparing all resistors from channel A to Channel B and cannot find anything out of bounds.

Any ideas on what to check next?

Thanks.

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