Found the schematic.
Hokay, let's do the pre-amp tubes first, then the power tubes
0 - power down the amp. Let it sit for awhile. There are bleed resistors in this circuit, so it should discharge after 20 min or so. It's also handy to do this to cool off the tubes.
1 - remove the tube shields. These are the metal covers on the pre-amp tubes. These are held on by a bayonet type lock. Push up, then twist, counter clockwise as viewed from the bottom.
2 - remove the first tube. Let's use the one on the end. Grasp it by the end and slowly wiggle the end around in a small circle while pulling it away from the socket. it should pull out after a few small circles. Note the position of the 'key' (the absence of a pin).
3 - choose the tube to put in it's place. You've got quite a variety there, so you can experiment. The first position is the most sensitive, so you want a quiet tube in there - but then I've also had good luck with high gain tubes in the first position. Pick one (i'd choose that mullard, actually. why not.).
4 - orient the new tube so the 'key' lines up the same way the old one was. Looking at the socket helps. it also helps to kinda put the tube in there with light pressure and feel if you're in the right spot or not. Once you feel you're in the right spot, apply some pressure with the same wiggle circular motion to insert the tube. It should go in with a bit of force, but you should not have to really push on it. It's a little bit more than, say, pushing in the cigarette lighter in your 68 'cuda.
5 - power the sucker up and give it a try. leave the shelds off for now. With the standby off, check to see that you've got the heater lighting. take it off standby and wait for a bit and see if it makes guitar noise. If so, have a beer and play for a bit. Then repeat 0 to 5 for the remaining pre-amp tubes
6 - re-install the shields. Ensure that the holes of the springs are going over the ends of the glass where the envelopes were sealed. This makes more sense once you have a look inside the shield.
Now the power tubes.
Well, turns out that this amp does not have a bias adjustment. The bias voltage is set to -46.7 (at least according to the schematic) and that's that.
sooo - you're taking a little bit of a risk here. If you have a bias probe, you can at least see if the bias current is in the ballpark. The probe should have instructions for this.
Now on to replacing the tubes
0 - power down and let it cool off. I'd let it sit for 1/2 hour so that those tubes are cool.
1 - There should be a spring lock holding the base of the tubes in. Push up on the wings of the lock to dis-engage it.
2 - grasp the end of the tube and use the same wiggle/circle motion while pulling to pull it out.
3 - do the same thing with the other tube (replace them in pairs)
4 - on octal socket power tubes, the key is a little "speedbump" that is on the circular alignment pin. Align this to the appropriate slot in the socket, and push the tube in, using the same wiggle/circular motion. again it should go in with that slightly more than a cigarette lighter pressure.
5 - repeat 4 with the other tube.
6 - power up that sucker. Wait for the tubes to glow.
7 - take 'er of standby and ensure that the amp is not freaking out with strange sounds, or that the plates of the new tubes are not turning cherry red on you. A bit of blue is OK. Cherry red is bad. If you see cherry red at any time turn it off.
8 - play some guitar. If it's sounding good, have another beer.
9 - play that sucker all night while continuously drinking beer, checking the plates of the power tubes to ensure they're not turning red on you.
10 - go to bed happy and drunk. The end.
edit - fixed spelling errors.
ccasion14:
