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conrad johnson help
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Old 23rd January 2002, 08:02 AM   #1
efoda is offline efoda
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Join Date: Jan 2002
Unhappy conrad johnson help

hello everyone,

i own an mv50 cj tube amp and a horrible thing happened...

my left channel speaker started putting out a very low, very distorted sound... this usually means that the plate fuse has blown... sure enough when i walked over to the amp i saw the little led blinking where the fuse holder is telling me it was blown...

but before i could power the unit down this flash and a crack, snapple, pop with burnt black plastic floating in the air... that pretty much ruined my day

i opened the case up to find the AC line fuse blown as well and several of the yellow capacitors (with the letters cjd .15uf 600v) burnt to a crisp... there are several browned spots on the board where it happened and i believe some of the smaller caps in the area also received some of the blow...

my question is... is this amp toast? how burnt is burnt... and what are some things to look for if its salvageable... any help would be greatly appreciated, i really loved this amp

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Old 23rd January 2002, 01:55 PM   #2
jam is offline jam  United States
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Location: Auburn, CA, USA

Replace all the damaged capacitors, resistitors and output tubes and you should be ok. Before you plug in the output tubes check the bias voltage, for problems in the bias circuit,
The only major problem I can see is if the output transformer is damaged but that is highly unlikely.

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Old 23rd January 2002, 04:06 PM   #3
GRollins is offline GRollins  United States
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Location: Columbia, SC
One thing to watch out for is the bias regulator. If it's shot, then the tubes will not bias. If the tubes don't bias, then you'll blow the new tubes as soon as you power it up.
Hate to say it, but if you're not familiar with the amp and its innards, it might be time for a trip back to CJ.
I took a lightning hit on my Premier One way back when. The next day, I turned it on and lost everything in one corner of the board...including the traces on the circuit board. Vaporized them. Gone. I was fortunate in that insurance covered it.

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Old 24th January 2002, 03:23 AM   #4
efoda is offline efoda
diyAudio Member
Join Date: Jan 2002
thanks for your help guys...

when i posed the question i was hoping that the both of you would answer... :-) that worked out real nice...

i may just have to send it off to cj, but, unfortunately i don't have a warranty for the amp and last time i spoke to them i was a little shocked by their estimate: around $500.

i wanted to see if it was at least fixable from you guys first... i'm a little intimidated to mess with it though, as my experience level is not very high and am a little apprehensive of just handing it over to a shop...

oh well, i do hear your advice though mr. grey, and if i were a little bit more experienced i would love to take yours mr. jam

thanks again
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