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Post by emilyhooker on Mar 28, 2012 1:33:27 GMT -5
So my Ampeg R212 Reverberocket has decided that after 1/2 hour of playing at mid to high volume, the volume will cut to barely audible. Full volume doesn't return until the whole unit has been turned off and fully cooled, which usually takes about another half hour to 45 minutes. Both the power and preamp tubes have been replaced, no visible corrosion on any jacks. Seems to only happen when it's played loud, ie running hot. Anyone have any ideas on what to trouble shoot next? (Other than swapping out the tubes, it's all factory original). Thanks.
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Post by JohnH on Mar 28, 2012 3:09:44 GMT -5
Hi Emily - welcome to GN2. That soumds like an interesting old amp. How old is it?
I'm no amp tech, but is seems like could indeed be a thermal issue, maybe a cracked solder joint somewhere that disconnects when it moves whn hot.
Stand by for more informed speculation from others....
John
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Post by reTrEaD on Mar 28, 2012 9:14:42 GMT -5
maybe a cracked solder joint somewhere that disconnects when it moves whn hot. Possible. Or a resistor that opens internally or a coupling capacitor that shorts when hot. |
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Post by reTrEaD on Mar 28, 2012 9:16:16 GMT -5
Anyone have any ideas on what to trouble shoot next? You could selectively heat individual components until you cause the symptom, then selectively cool (there are refrigerant sprays designed for just this purpose) to confirm that the you have the culprit. But unless you have experience, this is probably best left to a pro. |
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Post by yakkmeister on Mar 28, 2012 11:02:40 GMT -5
Anyone have any ideas on what to trouble shoot next? You could selectively heat individual components until you cause the symptom, then selectively cool (there are refrigerant sprays designed for just this purpose) to confirm that the you have the culprit. But unless you have experience, this is probably best left to a pro. Also, I'm not sure that's a great idea on tubes ... Could make the glass crack and, hey presto, need new tubes ... I had suspected the driver/phase inverter was overheating, poorly biased power-tubes (but then I would expect some crazy bad distortion, not loss of volume, so I don't this this is it) or event the rectifier tube (if you have one) failing due to overheating/overdrawing power tubes (pretty rare)... There's this too: www.geofex.com/ampdbug/lowpower.htm or: www.geofex.com/ampdbug/ampdebug.htmIf you want to check for other things ... Either way, looks like a job for a good repairman. |
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Post by sumgai on Mar 28, 2012 11:17:54 GMT -5
Emily, Hi, and  to the NutzHouse! Ampeg's in general have suffered two main problems over the years. Your description points to the outptut transformer, a usual weak point for many Ampeg combo amps. Have your repairman check it out after it's gotten hot enough to drop the volume. (I suggest this due to the life-threatening voltages present at this point. Unless you are a qualified tech yourself, then do the world a favor and play it safe!) However, sometimes the transformer is actually OK, but it's being driven to overheat by something called parasitic oscillations, which aren't all that common, but not unknown either. Your tech will need to use her/his oscilloscope to look for such. If the tech is still scratching her/his head after all that, let me know, I've got a few more possibilities... HTH sumgai |
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Post by reTrEaD on Mar 28, 2012 17:14:11 GMT -5
Also, I'm not sure that's a great idea on tubes ... Could make the glass crack and, hey presto, need new tubes ... Even without the risk of cracking the glass, this technique is not useful on tubes. Changing the temperature of the internal structure by heating or cooling the envelope is an extremely slow process. It would be like trying to affect the temperature of the contents of a thermos bottle from the outside. |
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Post by yakkmeister on Mar 29, 2012 0:30:36 GMT -5
Also, I'm not sure that's a great idea on tubes ... Could make the glass crack and, hey presto, need new tubes ... Even without the risk of cracking the glass, this technique is not useful on tubes. Changing the temperature of the internal structure by heating or cooling the envelope is an extremely slow process. It would be like trying to affect the temperature of the contents of a thermos bottle from the outside. Indeed - ergo, not the best idea for this amp ... Interesting point about the OPT, I didn't realise that Ampeg had issues with those ... |
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Post by reTrEaD on Mar 29, 2012 7:18:19 GMT -5
Indeed - ergo, not the best idea for this amp ... I don't follow your logic. This is still an extremely useful technique for identifying thermally sensitive resistors and capacitors. Tubes are (and except for the rectifier, have been) identified by substitution. |
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Post by yakkmeister on Mar 30, 2012 1:09:38 GMT -5
Indeed - ergo, not the best idea for this amp ... I don't follow your logic. This is still an extremely useful technique for identifying thermally sensitive resistors and capacitors. Tubes are (and except for the rectifier, have been) identified by substitution. yes, good point ... |
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Post by emilyhooker on Apr 18, 2012 4:54:11 GMT -5
Thanks so far for all the ideas. Solder's/capacitors appear to not be an issue. Now trying to find someone here in Portland, OR that is willing to really give the thing a good hard look, and not just flip it on/off and tell me it's fine. Oh, and answereing Jon H's question, it's one of the "newer" R212's, came off the line in 1992. Thanks again, I'll post back if I ever figure the darn thing out.  |
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Post by reTrEaD on Apr 18, 2012 8:56:03 GMT -5
Now trying to find someone here in Portland, OR that is willing to really give the thing a good hard look, and not just flip it on/off and tell me it's fine. A thorough explanation of the problem (like you did in your OP) will go a long way in determining whether the tech is competent. Leave your amp in the trunk of your car while you ask him how he plans to troubleshoot the problem, and listen carefully to his response. If he can present a sensible plan, bring your amp in. If he is vague or seems confused, drive on to the next tech. Looking forward to hearing how this one is resolved. |
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Post by sumgai on Apr 18, 2012 12:08:51 GMT -5
Emily, Long-time GuitarNut Teleblooz is also from Portland, OR. PM him for some advice on where to take your amp. I'm sure that between him and/or his bandmates, someone is gonna be able to set you up with a good tech. HTH sumgai |
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Post by Teleblooz on Apr 18, 2012 19:30:59 GMT -5
I recommend Inner Sound www.inner-sound.com/home.htmlThey're the authorized service center for a number of major brands, including Fender and Marshall. |
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