I recently was given this head by a friend. My dilemma is this: it needs new tubes, and possibly some other work. I simply have no idea where to start. What I do know about the thing is this: there are six spaces for tubes that are immediately visible, though empty, and the number "HH905343" appears on a yellowish round sticker on the back. It's got four inputs on the front panel, and both a standby and polarity switch. If anybody can tell me more about this amp, especially how I might go about making it playable again, I would be most grateful. Contact me with any suggestions or information at devlin_grunloh@yahoo.com. Thank you all in advance.