Name: Steve Kennedy
Email: steve@pacair.com
Subject: Preamp Tubes
Thread: 69
Time: Mon, 07 May 2001 01:05:22 GMT
With six small tubes, this is obviously not a Music Man amp!
If upon careful inspection you do not see ANY glowing heaters in a tube with the amp on (look at them from all angles in a dark room to verify absolutely NO glow. Some tubes have heaters that are hard to see in normal room lighting) then either the tube is bad OR there is a wiring problem or power supply problem.
This will vary depending on the amp's specific design. For instance, some older vintage amps used both 6 volt and 12 volt tube types, which can mean two different heater power supplies were required (or a series AC heater string for 120VAC operation). If all the 6 volt tubes didn't glow, it would probably be a power supply-related problem and not necessarily a bunch of bad tubes.
Not all "small" (preamp") tubes are 12AX7 types (although most probably are now days), so they may not be a universal answer to your problems.
If you have 3 Large tubes, two are probably output tubes (a matched pair) while the third tube is the rectifier tube. Otherwise, if you have a solid state rectifier, you are missing another output tube!
If none of this makes sense to you, then you should take your amp to a qualified repair person. Only a small percentage of amp problems can be fixed by replacing tubes. It is highly likely that some internal repair will be necessary.
The voltages inside of a tube amp CAN kill you, and your chances of injury and death are MUCH higher if you don't know what you are doing inside. Do yourself a favor and find a local repair guy!
Steve