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Super Reverb Biasing

muzacman02

Member
Messages
36
I own a 67' SR I need help with the Biasing and Bias Pot. I just installed a NOS Matched pair of 6L6's however when I set the Bias The bias Pot at Max Is about 38.0 ma. I set the Bias at 32.0 ma Is this Close to being Correct? I realize it may Be a Little on the Hot side but it sounds AWESOME! the Plate Voltage was about 435Volts. Can anyone help me to understand what the OPTIMAL Range should be for Great Sound and Long Tube Life. Thanks
 

DT7

Member
Messages
2,796
I own a 67' SR I need help with the Biasing and Bias Pot. I just installed a NOS Matched pair of 6L6's however when I set the Bias The bias Pot at Max Is about 38.0 ma. I set the Bias at 32.0 ma Is this Close to being Correct? I realize it may Be a Little on the Hot side but it sounds AWESOME! the Plate Voltage was about 435Volts. Can anyone help me to understand what the OPTIMAL Range should be for Great Sound and Long Tube Life. Thanks
Unfortunately, the truth is you're going to have to decide, up front, which of those two concerns is of primary importance...long tube life, or best tone. Until you make that decision for yourself, it's a difficult question to answer. I can say this...the best way to achieve both is to use good NOS power-tubes, and have them biased by somebody who knows what they're doing.
 

Blue Strat

Member
Messages
30,202
Simple answer: Somewhere around 35mA, for 6L6GC's, in virtually any amp is safe and ok. I'd go for 35mA and start playing.
 

jcs

Member
Messages
8,078
If it were a super high plate volt amp (like my 62 Bandmaster) i would go less than 35ma but i tend to bias as cool as possible without crossover distortion and loss of dynamics.

Some 6L6GC sound better biased hotter imo...i like RCA Blackplate 6L6Gc biased cooler....otoh i like Sylvania big bottle 6L6GC a bit hotter but its up to your ears and what works well for your style and amplifier.
 

pdf64

Member
Messages
7,519
What rectifier?
If 5AR4 then consider a 5R4 to bring the VB+ and so plate dissipation down some. It will shave a few watts off the power output, nothing significant.
Pete
 

ked

Member
Messages
911
At 32 ma with 435 volts on the plates you aren't anywhere near hot. You're only running a little over 46% bias.
 
Last edited:

DT7

Member
Messages
2,796
At 32 ma with 435 volts on the plates you aren't anywhere near hot. You're only running a little over 46% bias.
That would be 46% of what?

Point being that what constitutes "cold" and "hot" is going to vary between the tube in question, and varies between manufacturer and type within a given manufacturer, which varies with the year of production. Unless you have the actual spec sheet for the tube in question, within the same year, I wouldn't trust it.

In terms of actual dissipation (which has nothing to do with tone), what is hot for one is cold for another, or the other way around. Any one-size-fits-all answer or chart, while it may be close (or not), is not going to be spot-on accurate for anything.

To the OP, save yourself the headache and take it to a tech.
 

Blue Strat

Member
Messages
30,202
What rectifier?
If 5AR4 then consider a 5R4 to bring the VB+ and so plate dissipation down some. It will shave a few watts off the power output, nothing significant.
Pete
435V is already on the low side for a Super Reverb. No need to decrease plate voltage.
 

VaughnC

Silver Supporting Member
Messages
17,915
Keeping it under 35ma, fine tune it by ear. The goal is for the best tone not a magic number on a meter...your ear should know more about tone than a meter.
 

GearHeadFred

Member
Messages
1,648
Some guys run it up at 40, 42, some even higher. They say they like the 'greasy blues tone', whatever that means!

I personally feel like the Fender Blackface amps sound best biased on the coolish side. They start to loose the characteristic sparkle as the bias is set hotter.
 

smolder

Platinum Supporting Member
Messages
14,386
If you buy into a 70% dissipation number that the weber bias calculator puts out... that's a bit lower. In my bf-ish bassman I have the rca blackplates at 42 and 44 with 435 on the plates. Sounds damn good, which is the true test for me.
 

phsyconoodler

Member
Messages
4,315
Guys,guys,guys! It really depends on the tubes. Some tubes sound lame at 35ma and some are great.
I bias for tone and then look at the meter to see where they are.
It really does make a difference on what brand the tubes are,new production and old stock included.
Some tubes don't come into their own until 70% and beyond and then they really sing.Some are ready to blow up at 70%

So the Gerald Weber 35ma rule is preventing real tone from smackin' you upside the head!
 




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