Rebias Fender when changing power tubes?

Jerry Gleason · Post by **Jerry Gleason** » 25 May 2001 2:21 pm

Can any of you Fender tube gurus tell me if I can harm my Blues Deluxe by switching power tubes without having a tech adjust the bias current? I want to swap the 5881's it has now for some N.O.S. RCA 6L6CG'S.

I don't know the specs for these tubes, but the tube chart in the amp indicates either type is ok. I know rebiasing would be optimal, but am I going to burn up anything if I don't?

Thanks,
Jerry

Donny Hinson · Post by **Donny Hinson** » 25 May 2001 2:41 pm

The specs from the RCA tube manual shows the two tubes to be similar. No, you won't "fry" anything by making the swap. But, the tubes are far from "identical", so a bias adjustment should be made (and possibly a resistor change) for maximum efficiency.

Ken Fox · Post by **Ken Fox** » 26 May 2001 8:53 am

The Blues Deluxe does not have a bias adjust (the newer Hot Rod Deluxe does). Could not hurt to check bias and change bias resistor, if needed. Best idea, have a good tech add a bias conrtrol circuit! I did it to my 70's Twin Reverbs. It's nice to be able to adjust the bias for optimum performance and sound.

Danny Hullihen · Post by **Danny Hullihen** » 27 May 2001 5:37 am

Ken. That's excellent advice!

Lefty · Post by **Lefty** » 31 May 2001 4:25 pm

Fender claims that they now put color coded tubes in these amps so you can replace them with the same color and your amp should not require a re-bias. I have not tried it yet, but I have a hot rod deluxe and when re-tube time comes, I might try and find out. Could be a good marketing method to sell more tubes (no harm intended to Fender).