Inop K8010

After several years of successful and pleasurable operation I’m having trouble with one of my K8010’s

I had a Svetlana Kt 88 in V2 fail. This apparently took out R70. I replaced R 70 and replaced all the tubes with new JJ 6550’s.

All was well for a few months and then as I watched, R71 went up in smoke one evening. I replaced R 71 and now I don’t have any output from that channel.

All tubes light up, but LD 13 [the high voltage indicator] does not illuminate.

I checked the fuse as suggested in the trouble shooting portion of the assembly manual, and it’s fine.

I’m driving what is considered a “difficult” load, stacked Quad ESL 57’s, But up until now the 8010’s have performed wonderfully.

Have I fried the output transformer? :cry:

Thanks for any help.


Check high voltage circuit. Maybe the 5W series resistor is defective.

You can check the output transformer with a multimeter to check if a winding measures infinite or a very high impedance. Make sure to remove a transformer connections prior to measuring, to avoid measuring errors. Colour code can be found in the manual.

:smiley: Vel 417;
Thanks so much for the reply. Excellent long distance trouble shooting. It was indeed the 15 ohm 5w resistor. No physical evidence of failure, but it was intermittently open or of a very high value.

Could this resistor be the reason I’ve fried V2 in the past, and now V3 appears to be defective [ flashing blue color and gets hot rapidly ] I’m afraid to run it long enough to get any readings from V3, I’m waiting for delivery of a new tube before I proceed any further.

Thanks again for your assistance.

Hard to tell why the tube blew. Tubes do not have an eternal lifetime, and they tend to go with a bang, for no apparant reason, a bit like lightbulbs. Replacing the tube and the cathode resistor will most likely solve the problem. Check the negative bias circuit. Make sure all tube socket connections are OK. The power resistor blew because the tube blew, and not the other way round. Anyway, be extremely careful when fiddling around. The voltages in this amp can kill !