Is your u.l. triode switch rated for 450+ volts? Any chance it could be shorting to ground?
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I added (kind of) the last components to my take on the KT88 build and brought it up on my variac tonight.
Nothing exploded!
Compared to Marks (Blueglow Electronics) measured voltages I get some 10-15 V lower values all around, except for at the plates (pin 1 & 6) of the ECC85 where I have 27 V HIGHER value - 256 V compared to 229 V.
Should I be worried about this?
I have only tested the amp without a signal or load on the output yet, didn't have time tonight for a more thorough test.
Thanks!Nice job @Heffa. I think the reason your voltages are different is because you are using a 5U4? which has a higher voltage drop and more current draw than the GZ34 in the original.
Is your u.l. triode switch rated for 450+ volts? Any chance it could be shorting to ground?
You said in an earlier post that the GZ34 was humming. A bad rectifier tube would explain a few things. Mark the current one as suspect and try another.
That's not enough cool down time if the B+ has drained off. The heaters and cathodes are still warm enough to pass current into empty filters and you get a high current draw through the rectifier and outputs. You should give your amp at least a minute of cool down after turn off. The 5AR4 is a low internal resistance rectifier so it could need even more time to cool down depending on the load it gets from downstream. Amp to amp is different. 1 minute is minimum.
Good that you finally found the issue Bill, great work!