Time to Re-cap 50/50 power amp???

[higain_guitar]

Hi everyone,

A year ago, I purchased a used Mesa boogie 50/50 2 space rack power amp. I don't know its age but its probably about 20 years old now, as the last of the 50 50 s were made in 2001. (My serial number is in the 5700s.)

I put in new mesa 12ax7 tubes and new 6l6gc power tubes (nos mes str 420 tubes, grn, medium breakup). It sounds ok to me, but to be honest I don't know exactly how it should sound. I know these power amps were hand built like tanks but do you think the capacitors are still good at this point? Are 50/50 amps known for their longevity with caps or do you think its time to get it checked?

Any advice is appreciated, sorry I know so little about re-capping.

Thanks,
HG

 

[Henz]

Generally, filter caps need replaced every 10 years . Is it noisy on power up? Do you hear crackles and such? If so, it needs a minor tune up. I just re capped my 2:90 after 20 years new. But their were other issues with it. Leaky caps in switching matrix, arcing on pcb. Cracked B+ resistor. Anyway, this doesn't apply to you . Can you post picts of inside?

 

[higain_guitar]

Hi Henz, thanks for your help.

Below is a picture of the inside of my 50/50 power amp.

 

[Henz]

Your welcome. Looks very clean inside. Some people say that if it isn't broke, don't fix it. But for maintenance,it's a personal choice. When I re capped my 2:90, I had it all apart for other issues and since it was apart, I went ahead and changed every electrolytic cap. It wouldn't hurt to change your caps. Do them all. Even those two 47uf 100v bias caps. If you choose to do it, are you gonna do it? You have to lift the pcb which means lots of un soldering. You may not have to lift it but I believe those are through hole solder pads. Compared to mine, it looks relatively a lot easier. Take lots of pictures for re assembling. Take your time and you need good soldering skills. It was a tough fun for me. I learned a lot about my amp when I did it. Ask me any questions you can think of and I'll try to help. Jim

 

[woodbutcher65]

Coming up on 20 years? It's due. Though those caps are unlikely to leak or explode or fail catastrophically in the next 10 years, by now their performance is probably significantly degraded.

Recap it now and be done with it for another 15 or 20 years. Do it now while it's no trouble to get the parts.

Reality is that the electronics industry is ever changing. Parts that can be easily obtained today may be completely out of production 10 years from now. So if you do it now you're guaranteed to not have to deal with any possible parts problems for maybe 20 years or even more.

Putting new caps in at this point will most likely make for a noticeable performance improvement.

Get the replacements direct from Mesa. They use only best quality caps. And this is truth: You can't get better caps from another source but you can pay more for parts that aren't any better.

 

[Henz]

Woodbutcher , can I discharge my filter caps using a 470 ohm resistor with leads ? And if so, do I just put one end to chassis and then just touch the leads of caps with the other end? I always leave switch on standby , unplugged , and I insert a dummy load in speaker jack to help. Thanks, Jim

 

[woodbutcher65]

Yes, but I have yet to see a Mesa amp that doesn't have a discharge path to ground built right into it. After turning it off the caps should bleed off to ground over a period of several minutes. Using a bleed resistor can speed up that process but you may not need it.

Let your voltmeter be your guide. If you don't have a voltmeter, go out and get one.

 

[Henz]

Thanks for the reply. Yes, I have meter. Caps still have a charge after shutdown. But what's puzzling me is that after I bleed them with that wire I made, when I remove wire they recharge by themselves. I turned on all switches and continued to bleed. Eventually they got to a manageable level. Around 40 mV. Is that safe to work with? Thanks, Jim