AC30 Tube changing.

albriks · Posted: Thu Jul 27, 2006 2:52 pm Post subject: AC30 Tube changing.

Hi, everyone! I kinda need some advice here if that's ok? I bought a '64 AC30 a few years ago which had a top boost installed during the 70's I think. Anyway, I haven't been using it much until lately when I switched it on and to my surprise only half the volume came out of it. I'm guessing some of the tubes are busted, but I'm not sure. It still has the same tubes as when I got it so I've got no idea on how old they are.

I'd like to have them all changed as they seem to be of different manufacturers (12AX7 from both Sovtek and Fender (?) together etc.)

Here's the big question: Can I safely change tubes and instantly crank it up? I've heard that when changing tubes the amp needs to have its bias (or something) adjusted by a qualified person to prevent the amp from break. What are your thoughts about this? I don't want to lose my 42 year old baby!

Thanks in advance, people!

albriks · Posted: Sun Jul 30, 2006 1:51 pm Post subject:

Hi again...

Since posting this thread I have discovered that AC30s, AC15s and a bunch of other amps like Matchless DC30 etc. don't require bias adjustment when changing tubes. Which means I prolly don't have to take it to the shop after all. Apparently the tubes adjust themselves to the current or something, but I'm not entirely sure.

Does anyone have any good resources about this subject?

ChristianCM · Posted: Sun Jul 30, 2006 9:16 pm Post subject:

Hello Albriks,

Yes, no bias adjustment when changing tubes, but the most important (of course) is to choose 4 el84 matched.

Personally, I buy my tubes at watford valve(http://www.watfordvalves.com/home.asp), it's expensive but of very good quality.

For info, to choose el84:
http://www.watfordvalves.com/cgi-bin/documents/testreport_47.pdf
and ECC83:
http://www.watfordvalves.com/cgi-bin/documents/testreport_2.pdf

Regards,

ChristianCM.