Question about first tube change on a DC-5

LTE · Jan 5, 2009

I just got in the mail today my 6 tungsol 12ax7's, and 2 Ruby tubes 6l6's, i read in the manual about the fixed biases on mesas, and im kind of worried.

I might have misunderstood the manual, but do only mesa tubes not need to be rebiased in the amp or is it any type of 6l6, 12ax7 (What originally are in the amp)

So am i all set to change them? or do i need to take it to a shop?

Old BF Shred · Jan 5, 2009

When you bought the tubes, did you specify what amp they are to go in?
Mesa amps do not have adjustable bias. They must use power (not preamp) tubes within a certain "range".

FYI, this translates to rating 4,5 or 6 in GrooveTubes. And, of course, all Mesa tubes.

Going to a shop won't really help. As I said, Mesa amps don't come with a bias adjustment.

They may try to tell you to pay to have your amp "modded" to have adjustable bias. This, in itself, is not a bad idea as long as your amp is out of warranty (likely in this case) and the shop techs know what they are doing (assumed).

I did this mod to my 50/50 power amp, and it works fine.

How deep do you want to go into it? You may wish to contact the place you bought the tubes to see if they are the right ones or arrange a return.

The 12ax7's should work just fine as is.
Good luck!

LTE · Jan 5, 2009

Well i bought them on musicians friend, there was no option for anything, i bought these tubes btw

http://accessories.musiciansfriend.com/product/Ruby-Tubes-6L6GC-STR-Matched-Amp-Tubes?sku=212030

LerxstLee · Jan 7, 2009

LTE said:
Well i bought them on musicians friend, there was no option for anything, i bought these tubes btw

http://accessories.musiciansfriend.com/product/Ruby-Tubes-6L6GC-STR-Matched-Amp-Tubes?sku=212030

On the box or tubes they should have for example
IP 44
GM 6400

Do you have those numbers to post .

Old BF Shred · Jan 8, 2009

Musicians Friend is pretty good about returns. I'd call them to see what they recommend, if they know.

Otherwise, "MagicParts.com" is the distributor for Ruby. A call to them may help determine what your amp needs.

Mesa should be able to tell you what the idle current (IP) is supposed to be for that amp as well.
So what you got may be OK as is. Better to find out before paying return postage to MF.

BTW, I've heard some good things about those Ruby's lately so I hope it works out!

Good luck with that.