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Do you have to rebias when you change preamp tubes?

moonweasel

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My '66 Vibrolux has been pissy for years, and I have just sort of sidelined it. Coming to my senses, I was told that the tube for the tremelo/reverb circuit was on the way out and a few weren't far behind by a trusted tech back a few years ago.

Can I swap out the preamp tubes with identical spec replacements without any bias issues? I know next to nothing about tube amp issues, so please excuse my ignorance. :)

I am under the impression that rebiasing is only when you mess with power or rectifier tubes?

Thanks!

PS - Was thinking about just replacing my entire set of smaller tubes to make sure my bases are covered. My Normal channel has no issues whatsoever, but the reverb channel tends to be staticy and exibit old tube-ness. :)
 

MikeSlub

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You only need to re-bias if you swap power tubes.

If it's been a long time, you may want to also consider new power tubes and a re-bias. The power tubes make a difference in tone, along with the pre-amp tubes. :hank
 

Mitchell

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You only need to re-bias if you swap power tubes.

If it's been a long time, you may want to also consider new power tubes and a re-bias. The power tubes make a difference in tone, along with the pre-amp tubes.



Today 10:03 AM
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les strat

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I will tell you the BFVR's do sound so much better with NOS tubes vs the newer Russian and Chinese tubes. I had RCA's for the 12ax7's and some Mullards for the 12at7's. Good stuff. It might just kickstart and rekindle your interest in that wonderful amp.

You can also pull the V1 preamp tube completely out for a little bit more gain into the second (Vibe) channel.
 

Wally

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MY observation since it hasn't been mentioned....if that amp hasn't been recapped, that mgiht do more for the overall tone of the amp than anything else.
 

moonweasel

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Hey Wally, it was recapped in 2008, but my budget was super strapped and I couldn't do tubes at the time. Thanks for the heads up on that.

Les strat, I will keep that in mind. What do tubes like that go for? EDIT: Just looked at tubedepot, they are ~$150 (12ax7)? That's going to be way high for me.

What are the best, new production tubes for a BF VR? Thanks all.
 

moonweasel

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I woudl still love to know everyone's opinion on the best new production tubes, but I found these NOS which seem more reasonably priced. In fact, a memory just came back to me that I may have put a NOS Philips into this amp when I had it recapped, I think one of its tubes was truly dead at the time. (I found the amp at a garage sale in totally non-functioning condition).

http://www.tubedepot.com/nos-12ax7-jange.html

I think I will pop the back cover off and take some pictures of what is in there right now....
 
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moonweasel

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Ok Left to right, starting with rectifier:

RCA Gz34 USA
Slyvania 6L6GC USA
Slyvania 6L6GC USA
12AT7 PhilipsECG USA (I think this was replaced in 2008)
GE Elec___ 12AX7 USA (elec___ was illegible)
Slyvania USA
GE Elec___ USA (elec___ was illegible)
Slyvania 12AX7A USA
Sylvania USA.

I couldn't read the type on some of them. Also, why would the Slyvania 12AX7A have the A on the end? I thought they were just 12AX7... Thanks for the patience. :)


I believe the tech in 2008 made notes on the tubes in marker. One of the Sylvania's was marked "116" followed on the next line with "110B"... If that means anything to you guys, I can note the rest too...

Kind of fun to get the ole' girl out of mothballs. :)
 

Pat Boyack

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I have read that if the tubes are a matched pair then a rebias is not necessary. Somebody correct me if I'm wrong. :2cool
 

les strat

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I have used to Philips Jan preamp tubes. They were hardy tubes. Maybe not as warm as RCA's , but a good tube still. Maybe just buy and use a decent NOS preamp tube for your V2 (if that is the channel you plug into), and use something decent (JJ's, repro Mullards, Tungsol, etc) for the reverb slots, trem, and phase inverter.

For new production power tubes, it's hard to beat the SED Winged C's. They sound great in a VR.
 

les strat

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I have read that if the tubes are a matched pair then a rebias is not necessary. Somebody correct me if I'm wrong. :2cool

No. The plate voltage can vary. Tube matching is just that... 2 (or 4) tubes that are very close, but that new matched pair of Mullards you bought might not run voltage similarly to the old set of matched Sovtechs that just came out of the amp. Unless it is a Class A cathode biased amp, new power tubes = rebias. There are exceptions, like with Mesa amps. If you use their brand tubes in their amps, you don't have to rebias as their tubes are specked the same.
 

moonweasel

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Thanks Les. I would be willing to spring for the Phillips NOS for that V2 spot.

The Philips AT7's are very very affordable. Much more so than the AX7's.

Do you guys shop at TubeDepot? Thanks again.
 

les strat

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Thanks Les. I would be willing to spring for the Phillips NOS for that V2 spot.

The Philips AT7's are very very affordable. Much more so than the AX7's.

Do you guys shop at TubeDepot? Thanks again.

I have a few times. Sometimes I have found good deals there. I bought my NOS Mullards from BluesforStevie here on the forum. (got my NOS Mullard GZ34 rectifier tube from him!)

Make sure the V2 is a 12ax7. V3 and V6 are 12at7
 
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MikeSlub

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For new production tubes, I've had pretty good luck with Electro Harmonix brand. Have also used Tung Sols, but have had more failures than with the EVs. Lots of guys like JJ's, and they are okay, but they don't sound as harmonically rich to my ears as the EH tubes. :hank
 

les strat

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For new production tubes, I've had pretty good luck with Electro Harmonix brand. Have also used Tung Sols, but have had more failures than with the EVs. Lots of guys like JJ's, and they are okay, but they don't sound as harmonically rich to my ears as the EH tubes. :hank

Hey Mike, next time you re-tube that BFVR, try the SED Winged C 6L6's. They were very close to the old RCA's I had. Warm and glassy, but still had punch. I think you will likey. :jim
 

Pat Boyack

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No. The plate voltage can vary. Tube matching is just that... 2 (or 4) tubes that are very close, but that new matched pair of Mullards you bought might not run voltage similarly to the old set of matched Sovtechs that just came out of the amp. Unless it is a Class A cathode biased amp, new power tubes = rebias. There are exceptions, like with Mesa amps. If you use their brand tubes in their amps, you don't have to rebias as their tubes are specked the same.

Thanks Les!! :3zone :3zone

Sometimes I might put stupid stuff out there and if anything I can get the real scoop. Appreciate it.
 

MikeSlub

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Hey Mike, next time you re-tube that BFVR, try the SED Winged C 6L6's. They were very close to the old RCA's I had. Warm and glassy, but still had punch. I think you will likey. :jim

Les, thanks for the tip! :)
 

MikeSlub

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I have read that if the tubes are a matched pair then a rebias is not necessary. Somebody correct me if I'm wrong. :2cool

Les gave the right answer (yes you should rebias), but I must confess that I have changed power tubes in several of my vintage Fenders with matched sets and have not taken them to a tech to rebias them in many cases. I will probably pay for it some day.

But hey, I'm the same naive guy that in my youth thought there was no difference between a guitar cable and a speaker cable because they had the same kind of phone plugs on the end! Ran a 2 x 12 Bassman bottom with my Fender Twin for years that way, and thank God it never blew up! :) :2zone
 

les strat

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But hey, I'm the same naive guy that in my youth thought there was no difference between a guitar cable and a speaker cable because they had the same kind of phone plugs on the end! Ran a 2 x 12 Bassman bottom with my Fender Twin for years that way, and thank God it never blew up! :) :2zone

:rofl Me too! JCM 800 driving a 4x12 with a guitar cable! For 10 years.

Glad that Drake tranny was tough.
 
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