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

rockman627

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?

Hammond101
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.

Leftee
Contributing Member
****

VA

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




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