Name: Steve Kennedy
Email: steve@pacair.com
Subject: 212 HD 130 ... my killer amp !
Thread: 72
Time: Mon, 07 May 2001 01:28:24 GMT
Your amp was probably made between 1974 and 1977. Music Man amps made after 1977 typcially have the solid-state phase splitter circuit instead of the tube phase splitter. The "EX" means it was originally made as an "export" product (220-240Vac most likely).
That small tube is the phase splitter, not a preamp tube. It is designed for a 7025 or 12AX7 type. Your amp was designed for EL34 style tubes and these should be used unless the amp has been modified to use the 6L6 (the bias is different).
Which tubes you use are a personal choice. I would AVOID Chinese EL34 tubes as early generations of these simply couldn't stand up to the high plate voltage (700 volts +) you find in the Music Man designs.
Groove Tubes and Svetlana tubes would be good choices. Electro Harmonix and Sovteks would work as well. Keep in mind that you want matched quads. Groove Tubes allows you to specify the "hardness" of the tube in order to choose clean or or ealry overload types.
Groove Tubes and Electro Harmonix are both likely to be specially matched Sovteks, as nether company makes their own EL34 types at this time.
To determine the proper setting of your impedance switch, you have to know two things.... what is the impedance of the particular speakers you have and how are they wired. All of this was covered in previous messages and if you don't understand the concept then you will need help.
When in doubt, just put the switch in the 8 ohm position until you know for sure.
Steve