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Post by cbell2112 on Jul 10, 2019 7:18:14 GMT -7
Hi guys,
I have owned this amp for about 10 years without any problems except the rectifier tube going out and a fuse blowing one time. I've seen a few threads on my problems and have tried a few things but wanted to check before I start buying a bunch of new tubes. I basically have 2 relatively minor problems.
1) I get intermittent crackling when I switch the standby switch on/off. I thought maybe it was the power tubes so I just installed a new matched set which didn't change anything. I also get intermittent crackle when the amp is on when I twist the Reverb and Cut knobs. My first thought is that maybe I need a new reverb tube but I am not sure which tube is the reverb tube. Is it the 12AT7?
2) This has been happening for a while and might just be my location but I pick up radio stations through this amp. My other amp does not have the same problem. I guess that could be the reverb tube as well?
Will throw one more thing out there. There is tube diagram stapled inside the amp, it shows 2 ecc83's and 2 12AX7's which as far as I know are the same tube. Any idea why they would do that? I have 4 Tube Doctor ECC83's in there and 1 JJ 12AT7 currently.
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Post by daddyelmis (Greg) on Jul 10, 2019 8:34:40 GMT -7
Scratchy and crackly knobs is often a sign they just need cleaning. I’d start with cleaning and tightening inputs/outputs and cleaning the pots and switches. Spraying a little DeOxit and then working the knobs and switches does wonders. Ditto the inputs and outputs - spray a little into the connections and work a 1/4” jack in and out a few times. The knobs come off easily (set screws) to get at the pot shaft.
There’s a great annual maintenance vid from Doc that’s very good.
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Post by cbell2112 on Jul 10, 2019 8:50:19 GMT -7
I tried that but my knobs don't just pull off, there seams to be a little screw and I was unsuccessful in getting it loose. Maybe because it is an older amp.
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Post by daddyelmis (Greg) on Jul 10, 2019 9:04:58 GMT -7
You should just loosen that screw and the knob can be gently pulled off. Given the age of the amp threads could be locked up a bit. A small jewelers type screwdriver should do it. Maybe a small (very small) amount of WD40 put on that set screw would help loosen it (try using a QTip with WD40 on it to dab some in there).
Here’s the link to Doc’s maintenance video
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Post by cbell2112 on Jul 10, 2019 9:11:33 GMT -7
I will work on that. Do you know which preamp tube is for reverb? I think that may be the root of some of my problems.
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Post by KeithA on Jul 10, 2019 9:25:26 GMT -7
I will work on that. Do you know which preamp tube is for reverb? I think that may be the root of some of my problems. Should be the 12AT7
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Post by cbell2112 on Jul 10, 2019 9:30:06 GMT -7
That's what I was thinking but the diagram shows the 12AT7 as the 3rd out of 5 preamp tubes. For some reason I would think it would be last but of course I don't know anything about amp construction so just wanted to make sure.
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Post by KeithA on Jul 10, 2019 10:17:06 GMT -7
That's what I was thinking but the diagram shows the 12AT7 as the 3rd out of 5 preamp tubes. For some reason I would think it would be last but of course I don't know anything about amp construction so just wanted to make sure. No, the last preamp tube (closest to the power tubes) is likely the phase inverter.
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Post by digs57 on Jul 11, 2019 11:47:56 GMT -7
ive been using nos Phillips 12at7 wa....reasonable for nos...I usually replace driver v4 as well at same time.
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