JCM 800 clone

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Turd Ferguson
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JCM 800 clone

Post by Turd Ferguson » Sun Jun 12, 2016 12:19 pm

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

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herbvis
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Re: JCM 800 clone

Post by herbvis » Sun Jun 12, 2016 3:01 pm

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

Turd Ferguson
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Re: JCM 800 clone

Post by Turd Ferguson » Sun Jun 12, 2016 5:20 pm

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

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herbvis
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Re: JCM 800 clone

Post by herbvis » Sun Jun 12, 2016 7:58 pm

Turd Ferguson wrote: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!

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Re: JCM 800 clone

Post by Turd Ferguson » Mon Jun 13, 2016 3:33 pm

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

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neikeel
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Re: JCM 800 clone

Post by neikeel » Mon Jun 13, 2016 3:52 pm

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

Image

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

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

Turd Ferguson
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Re: JCM 800 clone

Post by Turd Ferguson » Wed Jun 15, 2016 8:43 pm

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
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Re: JCM 800 clone

Post by Turd Ferguson » Thu Jun 16, 2016 4:38 pm

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!!

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