FDP Home Page / FDP Forum / FAQ's

The FDP is made possible by the following companies and individual members like you.
Please use the links below to show them we value their sponsorship.

Yellowjackets Tube Converters



Antique Electronics Supply

Musician's Friend

Guitar Center

Amplified Parts

Apex Tube Matching

WD Music


Jensen Loudspeakers

* God bless America and our men and women in uniform *

* Illegitimi non carborundum! *

If you benefit and learn from the FDP and enjoy our site, please help support us and become a Contributing Member or make a Donation today! The FDP counts on YOU to help keep the site going with an annual contribution. It's quick and easy with PayPal. Please do it TODAY!

Chris Greene, Host & Founder



Find musicians
in your area!
  Search the Forums  

FDP Forum / Amp Mods, Repairs, and Projects / using different output tubes


New York

Feb 16th, 2017 01:09 PM   Edit   Profile   Print Topic   Search Topic

A slightly different question concerning my 6G12-A Fender Concert amp: before my replacement TAD 6L6-GC's arrived, I had a gig. It turned out I had 1 Sovtek and 1 Winged C that biased to -35mv and -33.5 mv so I used that combo for the gig and all was OK. The question is, will a problem eventually develop? Right now the TADs are in the Concert and the Sovtek/Winged C combo is in my DeVille.

In a similar vein, a friend found a bunch of tubes and gave them to me. In this bunch was a lot of noisy 12ax7s (RCA's and GE's), 2 RCA- 1 Kinsman- and 1 Realistic 6L6GC's. 1 RCA had a broken key but I figured out how to install it anyway. One RCA is a long tube the other shorter, but I just tested them now in the Concert and they work and sound pretty good. Except the bias on the short one reads -30mv, the other reads -52.2mv. Since they sound pretty good, I'm thinking of using them for recording, maybe an hour's worth of use. Is this feasible?

Contributing Member

So. Cal. USA

Feb 16th, 2017 02:41 PM   Edit   Profile   Print Topic   Search Topic

My advice would be to make sure the Concert has the correct main fuse in it. That tube drawing 52+ mv is on its way out. Your other matches are for the most part ok.

There are those who believe tube amps sound better with a bit of mismatch. I tend to agree 5-7 mv with 6L6 tubes is OK IMO.

As matched sets age this is about where you end up anyway.

Steve Dallman
Contributing Member

Merrill, Wisconsin

Age is just a number...mine is big
Feb 18th, 2017 07:35 AM   Edit   Profile   Print Topic   Search Topic

In the 60's when we'd take our Fenders in to the TV repair guy to be fixed, he'd replace any bad power tubes with whatever he had on hand, and set the bias voltage to the -52 or whatever on the schematic. Mismatched tubes of different brands were common. After I started working as a tech, I'd get Twin Reverbs in for repair with 4 different brands and shaped 6L6's.

I have an old pair of RCA blackplates that work fine, but draw a lot of current. They've been doing that for 25 years.

A gigging friend brought in his Super Reverb that started giving him trouble. He asked that I don't change anything as he loved the tone.

One 6L6 was drawing 52mA and the other 26. He wanted the same power tubes, so I wired his amp to have separate bias adjusts and set them both to 35mA. He was not happy. I had to mismatch them until he was happy, but it ended up not as severe as when we started.

Contributing Member


Feb 18th, 2017 08:57 AM   Edit   Profile   Print Topic   Search Topic

Very good point Steve! How many of those tones of yesteryear do we love that were created with amps set up like that?

FDP Forum / Amp Mods, Repairs, and Projects / using different output tubes

Reply to this Topic
Display my email address             Lost your password?
Your Message:
Link Address (URL):
Link Title:

Moderators: Chris Greene  Iron Man  reverendrob  

FDP, LLC Privacy Policy: Your real name, username, and email
are held in confidence and not disclosed to any third parties, sold, or
used for anything other than FDP Forum registration unless you specifically authorize disclosure.

Internet Application Development

Copyright © 1999-2018 Fender Discussion Page, LLC   All Rights Reserved