Had bias switch in wrong position on dual rectifier

[mitch103]

I feel like such an idiot but I just realized I had the bias switch on el34 when I in fact had 6l6 tubes in there. It was prolly in that position for close to 20 hours of amp time. Do you think I may have caused permament damage to the head? It still sounds fine but..
Just a little concerned.

[Andy92]

Playing an amp unbiased can cause the tubes to go faster, so you might have to replace one sooner because of it. But that's the main issue you'd run into. If the amp is running fine, you don't have anything to worry about.

[mitch103]

Thanks a lot, relieves some anxiety.. Im in the process of finding out where I can purchase the 6L6 12AX7 pre-amp tubes and 6l6 5U4GB's like mark uses on his rectos.

[Andy92]

Sweetwater carries them if you don't have issues ordering online.

[mitch103]

I actually ordered from there earlier today but called in and cancelled the order due to the fact that the tubes didn't specifically say 6L6 on them. What do you think?

[Andy92]

You could try calling them on a weekday to make sure of what you're ordering. They should have assigned you a rep when you made an account. They have awesome customer service.

I checked their site earlier and saw the preamp tubes said 6L6 12AX7. You could ask a rep about the power tubes just to be safe if you want.

[mitch103]

Could you send a link to those 6l6 pre amp 12ax7 tubes?

[Andy92]

http://www.sweetwater.com/store/detail/MB12AX7

6L6 is a power tube only by the way. You won't see a preamp tube with 6L6 or EL34 labeled on it anywhere.

[mitch103]

Ohhhhh. Thanks for clearing that up man!

[Andy92]

No problem! I forgot to mention that up front. Most amps only have preamp and power tubes, but the dual rectifier uses tubes for rectification (a handful of amps use solid state for this part). So you'll need 3 types of tubes.

4 Power Tubes (6L6)
5 Preamp Tubes (12AX7)
2 Rectifier Tubes (5U4GB)

[mitch103]

This whole time I thought the power tubes were the pre amp tubes and the rectifier tubes were the power rubes. Any safety precautions I should be weary of when replacing them?

[mitch103]

Also Andy I just found out you can buy all three of those sets of tubes from fret12, which I just did. About $200 all together. Can't wait to retube!

[Andy92]

I've never had to retune a Dual Rec, but in general you don't want to pull a tube straight out of the socket. You kind of rotate the tube in a circular motion as you pull up on it. Make sure the amp is unplugged from your power outlet. Depending on the location of the tubes, you might have to unscrew the outer part of the amp to get to the chasis. But for that I'd look around online. I'd imagine there are videos on YouTube of re-tubing that amp since it's so popular.

[mitch103]

Cool deal. I think I'm ready. Just waiting on the new tubes now!