MV55 Tube sockets issues.

[henry9731]

Hello everyone!

I got a used Mv55 for about half a year now, and recently it’s having some issues with the 12ax7 tubes.

First a pair was killed, then the replacement tubes were having “bad contact” to the amp, sometimes i need to wiggle it to have them going. Of course this leads of cracks and pops to the speakers.

Any clue if I should replace the 12ax7 sockets? Or if it’s burned components? Also should I run a small fan for the Mv55 or it’s not necessary?

[admin]

I myself am a MV-55 owner. The things you describe are obviously not normal or how this unit should operate. First and foremost I think you have already identified a faulty component(s), the tube socket. There should never be any need for "wiggling" to get a good connection to the tubes. I would start by replacing these and see if that fixes the problems. There are many 12ax7 socket connectors that you can buy from online dealers. Luckily, that is a standard component. You can go on a site like PartsExpress and find them there.

If you get lucky, that is all it will take. If there are more problems then further investigation will be needed but again, you have already identified a specific component failure so I would start with that.

[henry9731]

Would you say it would be a easy to do for a diy guy that knows nothing about amps? I mainly solder wires only, but I have no idea what to look for inside the unit.

[admin]

It should be pretty easy. It's basically nothing more than a swap. Make sure the unit is unplugged when working on it. I would manually discharge any of the larger capacitors for safety. After that, it's just desoldering the current socket and resoldering in the new ones.

[henry9731]

Unfortunately. I don't think it's a simple socket issue.
The right channel loses volume occasionally. I think it's related to unstable voltage.
There are also crackles and pops occasionally. And the bias light blinks when it crakles and pops...

[admin]

There certainly may be more problems. But if the tubes are not seated well due to the socket not holding the tube pins appropriately, then that is step 1. Fix the obvious problems first, and then re-evaluate.

[AnotherJohnson]

Unfortunately. I don't think it's a simple socket issue.
The right channel loses volume occasionally. I think it's related to unstable voltage.
There are also crackles and pops occasionally. And the bias light blinks when it crakles and pops...

In a unit that old, it could be any number of things.

The tubes are always suspect. But so are sockets, caps, resistors, switches, etc.

I had an MV52 years ago. It was one of my least well liked tube amplifiers and it soured me on that MV genre.

Perhaps you know this, but THERE ARE POTENTIALLY LETHAL VOLTAGES IN TUBE AMPS, even if they’re unplugged.

No, people don’t die every day from taking the cover off a tube amp. And there are some old heads who enjoy trading stories about how they were knocked on their a$$ by a shock, or who can show you an electrically fried bit that they watched explode. Surviving an adventure into a tube amp as a novice is common. However much dumb luck is better than skill, if dumb luck fails, it can be lethal.

So … as a foil to admin’s enthusiasm, I would advise caution. And in the case of these 30+ year old amps, I’d advise either sending them back to CJ for refurbishment, OR EVEN STRONGER, I’d advise selling the unit for parts. My last choice would be to make it a home project. Yes, I know there’s learning to be enjoyed … but in my opinion, the cost to benefit ratio can be awfully high.

YMMV

[henry9731]

I’ve asked a technician to replace the tube socket for the 12ax7. And the tubes no longer has bad contact. I also found the 6sn7 was dying, and was a part of the problem. All tubes in the system is now NEW.

However… the left channel is still phasing in and out after about 40mins of play time and eventually went into a high pitched signal noise and almost went dead.

The tech says everything seems fine and the caps were all in spec, no clue what is going on…

[AnotherJohnson]

Could be a cold solder joint or some other temperature sensitive issue.

It could take many hours to track it down. Not cost effective if you’re paying for the tech time (which is only fair).

I would go with “sell it for parts.”

[henry9731]

Jokes on you the amp wasn’t the culprit. It was the speaker.
Somehow I just realised I haven’t tried switching the LR output and when I did, it’s still the right channel.

I went behind the speaker and wiggled the binding post and managed to replicate the weird noises and problems. Retightened everything and now it’s up and running again!

[henry9731]

What happened with the Mv52 that turned things sour?

Apart from the loose socket I had, everything was spot on and nothing was burnt or out of shape. The seller kept it so clean it I was astonished when the chassis was opened.

[AnotherJohnson]

I’m glad you think you’ve got it sorted out. It sounds like maybe you’ve got stuff cobbled together so that you enjoy it, and really … for what more can one ask.

The MV52 list is too long to sort through. It doesn’t really matter to you anyway. I owned many of these 30+ year old units when they were recent, or still, current.

At some point I will learn that many of the posts on vintage gear are served undercooked. They have two pretty predictable endings. Either “Nevermind” or “how can I get CJ parts?”

Maybe a year from now you’ll still be trouble free. Best of luck.

I’d still sell it for parts. It is 15 years past my interest in old CJ.

[admin]

All's well that ends well! No go and enjoy the tunes.