| Author | Message | ||
| Jay Hammond (jead) Username: jead Registered: 01-2011 |
I have a 212-SixtyFive and a 212 SeventyFive. The 65 has the 12ax7 PI tube, reverb and tremolo - the 75 is SS pre, but has pahser and reverb. One has got to go. Which one should I keep and why? | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
Well, I'm partial to the tube drivers myself. Always felt that they were a little warmer. My 2-10-65 has the tube and I wouldn't have even bought it if it hadn't had it. That having been said, the SS driver circuit IS a little more dependable. I haven't had any problem with MINE but I do bias it on the cool side and it has a good old world tube in it. Some of the new stuff MIGHT not be as sturdy. That's my story and I'm sticking with it. Mike. | ||
| Lars Verholt (lmv) Username: lmv Registered: 11-2009 |
My 2 cents: The old and the new MM amps behave fairly equally when you don't push them too much. If you tend to play with the pedal closer to the metal and like the classic EC style dirt, stick with the 65. If you like the amp to stay clean over a wider volume range, keep the 75. I am partial towards the tremolo (and to a certain extent the tube distortion) so I would keep the 65 and sell the 75 to a pianner player. Just think of how cool you could make a Rhodes sound with a 212-75 and the phaser. Cheers, Lars Verholt "Hi, I'm Lars and I have an amp problem..." | ||
| Jay Hammond (jead) Username: jead Registered: 01-2011 |
Jeez - As soon as I start thinking about getting rid of one the 65 starts acting up. When I powered it up, after a couple minutes I started getting a siren-like sound out of it. It went away fairly quick and I figured it was maybe just from not warming up the tubes before jumping in. Next thing I know, after playing it for about 20 minutes I started losing volume and the speakers were sounding muffled and just bad - so I went to shut it down and YIKES - the heat coming off the back of the amp was pretty intense. The tubes (JJ E34L's) weren't looking red hot but they sure were throwing out heat. After letting it cool down for a while I swapped the tubes with a set Groove tubes (marked 6CA7/EL34) which were the tubes in the amp when I bought it a little over a year. Much to my surprise - the amp played fine and I had no heat or siren effect all. I guess one of the JJ's got cooked but I can't see any sign that either are bad - BTW I biased them about 6-7 months ago at 21ma. I almost always use the low power setting as well. One other thing, when the amp started acting up I switched over to the "clean" inputs and it sounded fine. What the heck is going on? Any ideas O wise and vastly more experienced Music Man guys? FWIW - The phaser in the 75 is really kind of growing on me, Good effect and the push/pull is also nice. | ||
| Jay Hammond (jead) Username: jead Registered: 01-2011 |
Any thoughts on the effect I described above?? | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
Unless you can catch it doing it while on the bench, it's kind of hard. You might try swapping in a known good 12ax7 for the driver. There have been reports of the drivers going bad and causing all kinds of trouble. Other than that, tracking can be a problem. It is kind of funny that you say the heat was intense because unless they are going chernobyl on you, they really don't run any hotter than any other amp. My first guess would be that it lost bias voltage for a bit and got hot. Maybe check the bias voltage on pin 5 with the tubes out to make sure it's stable and then re-tension the sockets. It could just be a loose socket loosing control voltage from a dirty/loose connection on pin 5. And I am certainly NOT very smart! Mike. | ||
| Jay Hammond (jead) Username: jead Registered: 01-2011 |
Thanks Mike - Socket tension sounds like it could be a likely culprit. I hadn't thought of that, but since the GT's were fine, I should be able to eliminate a bad JJ soon enough. I also have plenty of 12ax7's too and bias sockets as well so I'll see what I can do. | ||
| Jay Hammond (jead) Username: jead Registered: 01-2011 |
The bias control tanked on this and toasted a tube. Made for a good excuse to recap the the electrolytics as well. It's all fixed now thanks to Andy Fuchs and better than ever. | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
AHH. The old crappy bias pot. They were kind of cheezy on those amps. Personally, I'd just as soon have the bias circuit fixed so that it doesn't get dirty pot syndrome. Those were crappy little trimmers in there. There's almost NO current going through them but it seems like a better control would have been better. Glad Andy got you going. Knew it had to be bias related. These things are all just getting old(like me!).. Mike. |
Tue, 03/25/2014 - 09:35
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