Build Your Own Clone Message Board

This is what I would do next...

First, I think it’s important to always have a set of known good tubes when fixing an amp. So you might look at buying a backup 5Y3. This might not be the problem though. And since the existing tube is new, you should be able to assume that it’s good. Unfortunately, that’s not always the case with vacuum tubes.

I would run a signal test on the amp. But this is a little hairy on tube amps and I don’t really recommend it if you can’t follow the signal path through the schematic and are unsure where the high voltage is, and how you can protect yourself from it.

Another idea is to measure voltages while the amp is making the noise. See if any of the voltages are spiking or dipping during the crackle. I would attach test leads to my DMM so you can keep a safe distance. Read the DC plate voltage of each tube. Read the 6.3 volt AC circuit voltage (not to ground, across the two green transformer wires). Read the 5 volt AC rectifier heater voltage (yellow wires).

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MasterDelayer/Reverbrador/Ampaholic/TopJacker