| Author | Message | ||
| LongFrost |
Hello, I just purchased a MM sixtey-five 112 with the 2275 chassy and the 12ax7 phase inverter. When I got it home and flipped it on hi the output tubes were nucleur. I pulled the chassy out, turned the bais down and the tubes cooled down when I turned it back on. The amp does not sound right. there is a noise. I have read the bias method and have stared for far to long at the schematic looking for the 10 Ohm resistor that I would be using if I could find it in the amp. I bought it form Daddy's and have a service plan. the problem is I have a gig next weekend and want try and correctly bias the amp before giving up the ghost and shipping it out for for weeks. If some one could explain in detail where the relative component is I would be greatful. I have a feeling that there is more wrong but this would possibly rule out the out put tubes as the source of the problem. The amp creates a noise after a note is played. It is somewhat metalic in nature, but could be electircal. I have a Silvertone 1484 head that does the same thing. Help please. | ||
| Langley |
The 10 ohm 1 watt resistor is conneted, on one end, between the 2 tube's plates (pins # 8). This is point "Y" on the schematic. The other end of the resistor goes to ground. I usually read 0.5V at one of the pentodes # 8 pin. Probably need to re-tube, including the 12AX7. | ||
| alex davis |
i went thru 3 full tube replacments and bias jobs locally on my 112/sixty-five before i found this site and sent it to terry... he found some other underlying component problems, replaced them all, re-tubed, biased... it's worked perfectly ever since jan '03... actually better than it's ever sounded. alex | ||
| Langley |
Oops! Pin 8 is the cathode. | ||
| LongFrost |
so' what was the underlying problem in yoour 2275 Alex? I'm giving up the ghost. one of the 3.9K bias resistors is roasted. Thank god I bought the service plan. The pc board under all the resistors around the bias trim pot looks like it got real hot once. Probably what roasted the original op transformer. I had 2 hd130's a few years ago that I had to seel. I almost have a 2275 in my rig, three years of piecing it back together, the final major player in the signal chain..... you must be pateint Luke....the Force, remember the Force........ I think the amp has got that voodoo in it some where. the other two did. My girlfriend goes, just take it back, buy something else. Tried to explain the virtues of the 2275, it's incresing rarity, get something else she said. I .....remember the Force Luke. When did MM introduce the yellow capacitors in these amps. What are the chances of me finding another op tranny for this that is original and good? Does MM/earnie ball still have any transformaers left fron the buyout? Could some one Eamil me the clapton mod schematic? | ||
| LongFrost |
Mine also has series speaker jacks. | ||
| Langley |
>"What are the chances of me finding another op tranny for this that is original and good?" POOR. >"Does MM/earnie ball still have any transformaers left fron the buyout?" NOPE. | ||
| John Drexler |
You can buy a 3-65 OP tranny new from Mojotone.com...they're made by Heyboer and are reputed to be better than the originals. They run $75. I just got through pricing one for my 65-112 (also has a 12Ax7 PI tube in it). Do not, I repeat, do not buy one from handwoundtransformers.com. They ripped me off big time...sent money months ago, still waiting for a "2-3 week delivery" and they won't refund. Go to the "Transformers" thread on this site and look under "after market transformers"to see this saga. You can also, by the way, purchase a 3-65 OP tranny (which is what my schematic says is original, although my 65-112 came with a replacement 5-75 in it) from Mercury Magnetics (.com) for $149. Good luck on your repairs! |
Tue, 03/25/2014 - 09:58
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