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Hi all,
Just finished my first amp build, a JCM800 2203 kit from Triode USA, which surprisingly enough worked first try. I've been playing it for a few days and it sounds and plays great, but there are a couple (hopefully) minor issues which came up last night when I was using it. I just installed retainers for the power tubes - not the simplest thing to do after the amp is wired up inside. Put tubes back in, let it warm up for maybe a minute, and turned off standby with no guitar plugged in. Silence for a few seconds, then an intermittent crackling sound, and a couple loud-ish pops which manifested themselves as blue flashes in one of the EL34s. I put it back in standby for another few minutes, then turned back on, silence, plugged in and it sounded fine for about 15-20 minutes of loud playing.
I've heard about old amps being cranky and noisy for the first few minutes of use, until they warm up properly or whatever, but this guy is brand new. My first thought is a bad connection somewhere, specifically the 1-ohm resistors on the power tubes, which are grounded to the tube socket bolts, which I had to remove and put back on while installing the retainers. I measured 1 ohm from pin 8 of all sockets to ground; could an intermittent connection here cause one tube to pop and spark/flash like that? Also: is there a chance of damage being done to that one tube?
The chassis has 5 holes pre-drilled for bias test points, which I'm not currently using, but probably will eventually, if only to free up some space around the power tubes. It would also reduce the number of ground connections which could possibly fail.
Another thing I've noticed about this amp is that when you flip it to standby, the guitar sound fades out as expected, but then if you turn off the mains power a few seconds after, the guitar sound comes back in and then fades out again. I'm guessing this is due to some aspect of the circuit, but I'm interested to know why my other amps don't do it.
Circuit layout, by the way: http://site.triodestore.com/JCM8002203AV2update.pdf
Just finished my first amp build, a JCM800 2203 kit from Triode USA, which surprisingly enough worked first try. I've been playing it for a few days and it sounds and plays great, but there are a couple (hopefully) minor issues which came up last night when I was using it. I just installed retainers for the power tubes - not the simplest thing to do after the amp is wired up inside. Put tubes back in, let it warm up for maybe a minute, and turned off standby with no guitar plugged in. Silence for a few seconds, then an intermittent crackling sound, and a couple loud-ish pops which manifested themselves as blue flashes in one of the EL34s. I put it back in standby for another few minutes, then turned back on, silence, plugged in and it sounded fine for about 15-20 minutes of loud playing.
I've heard about old amps being cranky and noisy for the first few minutes of use, until they warm up properly or whatever, but this guy is brand new. My first thought is a bad connection somewhere, specifically the 1-ohm resistors on the power tubes, which are grounded to the tube socket bolts, which I had to remove and put back on while installing the retainers. I measured 1 ohm from pin 8 of all sockets to ground; could an intermittent connection here cause one tube to pop and spark/flash like that? Also: is there a chance of damage being done to that one tube?
The chassis has 5 holes pre-drilled for bias test points, which I'm not currently using, but probably will eventually, if only to free up some space around the power tubes. It would also reduce the number of ground connections which could possibly fail.
Another thing I've noticed about this amp is that when you flip it to standby, the guitar sound fades out as expected, but then if you turn off the mains power a few seconds after, the guitar sound comes back in and then fades out again. I'm guessing this is due to some aspect of the circuit, but I'm interested to know why my other amps don't do it.
Circuit layout, by the way: http://site.triodestore.com/JCM8002203AV2update.pdf
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