Dead Mark IIA

[krcassid]

I just changed the speaker in my Mark 2A (JBL to EVM 12L). I played it for a few minutes and it just faded away to nothing over 3-5 seconds, accompanied by a bit of an electrical-burning type smell. The amp has worked great for years. I have not changed the tubes in a long time because I don't use it that much (too loud for most apps).

I'm concerned about the smell. I turned the amp off and then and back on for a minute and didn't smell the acrid smell again. Can tubes make this smell when dying?

So, what do I do? Start replacing tubes (and, if so, which ones in what order)? Or, take it in to a pro?

Thx!

 

[zodiac272]

You can change the tubes yourself...pull the output tubes, then replace the preamp tubes.... after that put new output tubes. also check to see it the fuse blew. You may have blown a resistor in the power section. If you haven't had a service in a while, you are probably due. I just talked to mesa, and they are running 2 weeks turnaround time... pretty fast. if you send it there, you will basically have a new amp after they are finished. or find a local mesa auth. repair shop... where are you located?


scott

 

[krcassid]

Thx Scott. I'm in Portland OR. We don't have an amp tech here that I'm thrilled with. Mesa has an authorized repair facility but I don't trust them from past experience.

I just checked the tubes with the amp turned on and the power tubes are not getting warm or lighting up. Lights/ fan go on so it's not a fuse. Does this tell you anything?

I just sent my Triaxis to Mesa and they did an excellent job in 2 weeks. So, if this sounds like more than tubes, I'd prefer to send it there.

Heck, it's a 30+ year old amp. I've had it for 7 years w/ no service and I don't know about the guy before me. Unless someone out there recognizes this scenario and has an easy fix, It's probably smart to get it checked thoroughly.

 

[tvhk1989]

I just had the same thing happen to my .50 cal, the filter caps in the power supply went, they only really have a suggested lifespan of about 10 years then they should be replaced so it could be that, does it pop fuses?

 

[kdorsey]

If you can go without it for a couple of weeks, a trip to Petaluma would be a good idea. You've probably fried a resistor, completely or partially, and it needs to be addressed. That also means that you need new power tube(s). perhaps you could send it without power tubes and have them replace those too? Otherwise, it's not a big deal and pretty common, especially for the older amps. It's time for a checkup.

 

[zodiac272]

hey,

what happened that you were unhappy with mesa? Mike Bendinelli is their mark series guru. you could probably ask that he do the work, unless they have someone better for the IIA's. chances are that it's never been in for a full service... a great testament to how well built it was. If you feel like you could pull the chassis, and have a look to see if something looks fried. I wouldn't recommend touching anything inside cause you can die if you somehow discharge a cap into your body. but if you send it in, you will save a ton on shipping by just sending the chassis. just pull the tubes, and loosen each screw bit by bit until it's resting on the 2 supports. then pull the reverb RCA and fan cords and slide it out. if you can post some close up pics. but don't do this if you feel unsafe.

scott

 

[krcassid]

Thx guys! Great advice. It'll be going back to Mesa on Mon as soon as I can get an RA. I'm actually kinda looking forward to it as I figure it'll probably come back sounding better than I've ever heard it!

what happened that you were unhappy with mesa?

I was never unhappy with Mesa. I actually said they did a wonderful job on my Triaxis just weeks ago. It was their local "authorized service" here in town that I don't like. I asked them if they could service the Triaxis. They said "yes". I asked them if they'd worked on one before. They said "no". I gave them a PA speaker (a Mackie) 2 months ago. They are still trying to figure out how to fix it. Portland is a relatively small city so we don't have many amp techs. The good one I know is out months (probably because he's the good one ).

Mesa in CA is outstanding. I'm looking FW to getting my Mark checked out.

 

[krcassid]

I do have a question Re: Tubes. I would like to take this opportunity to re-tube the amp. Typically, I've used JJs. Do you guys think that the Mesa tubes are as good as (or better than) the JJs? If so, I'll just let them do it when it's serviced.