JCM 800 clone

[Turd Ferguson]

I got a friends 800 clone and it blew the HT fuse so I figured it was a power tube. swapped out for a new set of both pre and power tubes, when I powered it up did not blow fuse but as I went to bias the new tubes it made a sound like a motor boat thru the speaker the hotter I bias it the louder it got I also seen a flash inside one of the power tubes any suggestion where to start?

Thanks

[herbvis]

I would compare voltages in the amp to the metro 2203 kit voltage chart. Then go from there.

[Turd Ferguson]

Thanks I will check, also the amp was working fine before it blew the fuse

[herbvis]

Thanks I will check, also the amp was working fine before it blew the fuse

Thats a good thing lol! Checking voltages should get you pointed in the right direction. Look closely to make sure there isnt a loose or damaged solder joint somewhere. Also a visual inspection for loose debris or solder that may be causing a short. How "clean" is the work inside the amp? Post some pics too. Lots of people have eagle eyes here and can spot anything that mi ght be off. Good luck!

[Turd Ferguson]

Hey dude where can I fine the voltage chart for the 800? it is a 50 watt clone!!

[neikeel]

This will be close, but of course it depends what trannies were used.



Or here is Mark Huss's version with higher voltage trannies:

http://mhuss.com/MyJCM/vchart.html

[Turd Ferguson]

Neil,
I check all voltage and on V3 phase inverter pins 2 and 7 are reading 24.0 volts the chart on pin 2 & 7 shows no voltage!! on V2 pin 2 I am getting 6.0 volts chart shows no voltage also!! now this is a EL34 tube amp and on pins 3 & 4 are about 100 volts higher then the chart shows.

Thanks Neil

[Turd Ferguson]

ok got the noise to go away it was the brand new PI tube it is dead!! I put a good tube in and I am now able to play it but it went from a great sounding 800 to almost an unusable amp!! it sounds congested like it has a cold the gain is unusable past 2 not sure what is wrong!!