Your answers to questions in Premier Guitar have left me to believe that you might know what I am hearing when I use my Peavey Classic 50/410 combo. I love the tone that I get, but there seems to be an intermittent swirl sound that happens while I am playing. It doesn't affect the amped signal, but is in the background. Sort of like a spacey, swishing hum from a bad ground. I have taken a mirror and tried to watch the tubes to see if one is having a fit and have seen nothing. I want to get the clean sound and not have that underlying noise. It doesnít matter if I am on channel one or two, have reverb on or off, in bright or normal channel. I have it just through the combo or with the 410 extension cabinet. Also here in Central Illinois, I donít know of any good techs to take it to for repair. If you could give me an idea what it is that is wrong and where to start looking to get this fixed I would really appreciate your advice. I just looked at the web site for Mercury Magnetics upgrades and was wondering if you had any experience with their claims. Sounds good, but is it worth it? -- Dan
Thanks for reading Premier Guitar and also my "Ask Amp Man" column. Glad you enjoy it.
There are a couple of possible causes for such a symptom. I would say the first, and most easily remedied, would be a faulty tube. Many different types of noises can come from tubes, none of which could be visually determined. The first thing I would recommend would be to clean the sockets and replace the EL84 output tubes in the amp. These tubes take the most beating and should be replaced more frequently than the preamp tubes. You did not mention the last time you had done this, but a good rule of thumb nowadays is six months to two years, depending on how often and how loud you play.
In order to clean the sockets, obtain some electrical contact cleaner that does not contain lubricant. Remove the tube, spray a decent amount of cleaner into the socket and cycle the tube in and out of the socket six to ten times. Leave the tube out of the socket and move on to the next socket. When all the sockets have been cleaned, leave the tubes out and give the sockets ample time for the cleaner to evaporate -- maybe fifteen to twenty minutes. Install the new tubes, fire up the amp and see if this has cured the symptom. If not, I would next replace the 12AX7 preamp tubes. One thing to remember, however, is that a new preamp tube can also produce different types of mechanical or microphonic noises. If your original symptom has been eliminated but the amp is now producing a metallic ringing or starts feeding back, move around the location of the preamp tubes to see if you can place the offending tube in a less sensitive location. If neither of these alleviates the symptom, at least the amp has a fresh set of tubes and should sound great once the cause has been found and the problem remedied.
To further explore the possible causes, I posed your question to John, an engineer friend of mine at Peavey, and I believe we may have another possible answer for you. The Classic 50 uses a wire connecting the preamp circuit board to the output tube circuit board, which provides the ground connection to the output board. This should be a black wire utilizing a white plastic connector approximately one inch long and attached to J74 on the output board (if marked). The recommended way to repair this potential cause of the problem is to upgrade the connection by removing the connector, stripping the wire and soldering the wire directly to the pin on the circuit board. This will provide the best, most reliable ground connection, without the worry of oxidized or intermittent connectors. This may be a larger task than most players are capable of and servicing tube amps should not be undertaken by anyone unfamiliar with the hazards, so find an experienced service technician to perform this kind of work. Regarding your question of such a technician in Central Illinois, I personally do not know anyone in that area. However, I'm sure if you inquired in any of the various gear forums you would find someone who is trusted.
To the last part of your question concerning the Mercury Magnetics upgrades: I have used their replacement transformers in the past and they definitely make a wonderful product. While I have not had the opportunity to install one of their recent upgrade kits, I have heard from players who have had the opportunity to compare stock and upgraded amps side by side, and they tell me the difference is quite noticeable. One even found it hard to believe they were the same model amps -- so I'd have to say that if you have a discerning ear, it may be a worthwhile investment for you. I hope that helps you restore your Classic.
Source: Premier Guitar
Edition: March 2009
©2008 Jeff Bober