| Author | Message | ||
     Danny Hescock (danny_hescock) Username: danny_hescock Registered: 11-2010 |
Hi guys, I just came across a MM112 Sixty Five (I believe its a 74-77 by what Ive read on this site) Great sounding amp, no scratchy dials, deep/bright switches worked, all inputs worked. I checked it out well before trading an amp for it (good friend traded it to me, and I made out good in the deal) So I used it for a bout 5 hours of playing total over a weekend. When I used it on Tuesday night it worked and sounded great for one song, then it started to fade in sound (from a good volume to nothing in about 10 seconds...with an "electronic smell" no smoke or burning, just a very "hot electric" smell) It happened while playing with the band so by the time I got the guys to be quiet for a minute the sound died and a few seconds later it powered down. It would not power back on. The tubes were glowing orange, but it did seem one was a bit brighter than the other, but this was only right after it powered down, I did not see them when it was powered to know if they had already started cooling down. Obviously I am heartbroken, but absolutly willing to try and get this guy running again. I have a few friends who are amp savvy, but was wondering if you guys had any ideas what this could be? Thanks a million for even reading this, hope to hear ANYTHING! | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
I would say you had a tube go up in smoke and take out the fuse. Replace the tubes, fuse, check bias and bias it cooler. This became kind of a problem with MM's back in the day, which was one of the reasons they went to the SS driver. PROBABLY didn't do any major harm but I'd check the resistors on the tube sockets also before I fire it up. Had that happen to one of mine several times and it survived right up until the time that I screwed it up myself! | ||
| Danny Hescock (danny_hescock) Username: danny_hescock Registered: 11-2010 |
Thanks Mike, I appreciate your info - Im hoping its nothing major as I got this thing for a steal and it is such an amazing sounding amp. Thanks again, I will update with info when I get it checked out. Happy Thanksgiving! | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
Forgot to ask-when you say 74-77, I'm ASSUMING it has the 12ax7 PI tube? I would suggest also that you check and make sure that you have sufficient control grid voltage before you fire up another one. Pull the power tubes out and measure the negative voltage at pin 5 and let me know what it is and if it's the same on both tubes sockets. That's your control or bias voltage. | ||
| Chris Haines (chris) Username: chris Registered: 02-2008 |
The same thing you describe, bright orange glowing tubes and power loss, has happened twice to my 410HD 130 (PI tube) but I was lucky to catch it very quickly before anything was damaged. I followed the advice of some on the site and bought a cheap plastic clip on fan. Previously the top of the amp was very warm to the touch and now with the fan its quite cool. I've had no problem since and use the amp quite a bit. I bought the amp in 78 and its interesting that I never had any problem with it until about 4 years ago. I used the amp a lot for the 1st ten years, it went into hibernation for the next 12 or so years and now I'm using it consistantly again. I replaced the original set of tubes about 8 years ago (various caps replaced also) and again about 3 years ago. | ||
| Danny Hescock (danny_hescock) Username: danny_hescock Registered: 11-2010 |
Thanks Guys, I am in contact with someone now who may be able to help me out (Terry Loose, yeah THE Terry Loose!)...I got his contact from this very site and am looking into how I could get it fixed. Ill update with more info when I have it! |