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Old 27th February 2012, 09:47 PM   #1
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Default Help with Conrad Johnson

A few months back, several of the member here were able to help me with a repair of my Conrad Johnson MV100 tube amp. Well it played quite well for several months and then problems. I powered it on and on the channel which was repaired it seemed as though I had a bit of popping and static in that channel, which would be the right channel. Now if you tap the chassis of the amp it would go away.

As suggested by several of the member it could be cold solder joint on the output tubes. well I re-soldered them and I got worse, but the tube sockets seemed to be pretty beat up. Ordered some new Ceramic tube sockets PRETTY!!! Spent hours changing, cleaning and installing the new one, Powered her up and the same problem.

What is happening is I am getting a loud squelching static and all of the bias LED's and coming on!! Both channels. For the love of GOD, I have no idea what is going on. Filter caps or coupling caps, seem like something in the bias and output stage.

If anyone can help it will be greatly appreciated, at this point I am about to to box up and put away for good. It's really not worth the time and money any longer.
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Old 27th February 2012, 10:26 PM   #2
Zen Mod is offline Zen Mod  Serbia
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huh ........ oscillations ?

do you care to put a link to previous thread , for pictures and schm ?
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Old 27th February 2012, 11:21 PM   #3
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Default schm

Thanks I am posting the schematics
Attached Files
File Type: pdf mv100schm[1].pdf (83.0 KB, 145 views)
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Old 28th February 2012, 12:13 AM   #4
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Did you check the input tube (5751 - 6FQ7) sockets? I've also had some tubes exhibit static/popping especially when tapped.
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Old 28th February 2012, 12:44 AM   #5
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My friend i have exhausted all option right now!! The damn thing glows like a Christmas tree on the leds and the noise is ear splitting.

Not to sure where else to check right now.
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Old 28th February 2012, 01:53 AM   #6
tomchr is offline tomchr  Canada
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Have you checked all the power supplies? If the D or G supplies failed, the bias LEDs could turn on. I'm guessing the LEDs indicate a case of over-bias... I'd put an oscilloscope on those supplies and watch as the amplifier makes scratching sounds.

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Old 28th February 2012, 02:29 AM   #7
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1st remove V1 and V3, Is the sound still there? If so, disconnect one end of C24,C25,C26 and C27. Is the sound still there? By disconnecting those caps, you are seperating the phase inverter and preamp from the output stage. This will help you determine which half to focus on. (those caps are also suspect)
By removing just V1 and V3, you are eliminating the load on the plate and cathode resistors of those stages, indicating either faulty pre and phase inverter tubes or scratchy resistors. If you remove the output tubes and this noise is still present, You may have internal leakage in one output tranny.
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Old 28th February 2012, 03:06 AM   #8
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Well a bit of history, I did power the unit up with no output tubes and no scratchy noise or bias led. I will try to remove the V1 and V3 and see how it goes, it just has me scratching my head.
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Old 17th March 2012, 03:25 AM   #9
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If I'm not intruding on the exchange ... Dhunte21, did you decide to keep the amp? I am looking for a tubey-sounding amp, so let me know if you decide to get rid of it. If it ever worked, what did you think of it?

Also, did you consider sending it to CJ to get fixed? Very non-DIY of me to ask, but ...
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