Difficult to Reproduce Issue

[ashbrook.m]

I have been using my Kaiju with both upgrade kits for the past few years with a weird issue I cannot seem to chase down.  The left channel has always taken a little longer to warm up but every few months it will take 5-10 minutes before an audio signal passes out on the left side. It will come on with a “pop” and then work perfectly for months.

Swapping outputs shows that the issue is only with the left channel. The heaters are glowing on all tubes. I cannot tap on either left chanel tube and get any microphonics when it’s not working. By the time I get it down to my bench and check voltages, they all are in spec. Any thoughts on this?

[Thermioniclife]

Did you swap the tubes and see if the problem follows the tube? I say that as you said that all your voltage tests are good, perhaps checking the resistance checks would be in order. also I think you should clean the tube pins and socket pins with an electronic cleaning solvent.

[Doc B.]

That's a bad connection somewhere. Cleaning pins as suggested is a good place to start. If that does not resolve the issue you may need to power up the amp with tubes in it and check the voltages. If you find that some voltage is not coming up properly you can start to check the left channel circuit for suspicious solder joints.

[Paul Joppa]

No microphonics when tapping the tubes suggests the bad connection is between the output transformer and the speaker.

[ashbrook.m]

Thanks! I cleaned the contacts and swapped the tubes. Will continue to track it down and check the transformer connections .