FENDER EVH 5150 III biasing

  • Thread starter Thread starter deadweight
  • Start date Start date
D

deadweight

New member
I know alot of people say these amps are biased "cold" from the factory but ive read a description of the amp now which includes this statement "Custom made transformers and special biasing help achieve Edwards fabled Variable AC effect". Im wondering if this is the reason for the "cold" biasing. Does anybody here know anything about this?
 
Amps that rely on massive amounts of preamp gain are usually biased cold to allow a clean power section.
 
The 5150 III 50 watt is biased at 30mA or so. Someone on here or the gear page posted a pic of the amp with a meter on it. It also has a bias adjustment pot as well. Again, there is a gut shot out there showing it...
 
Yes, I went through this a while ago.. you can bias them, there's a trim-pot inside and two test points. Mine was biased extremely cold, like 15mA / tube... The Fender service guide for it says they should be 20mA from the factory.. this is the 100 Watt I'm speaking of. I put mine around 22.
 
Should find out what the plate voltage is....then bias it
 
Ex: Average plate voltage-475VDC
(.6 X 25W)/475V then the bias would be set @ 32 mA for a 60% idle setting
(.7 X 25W)/475V then the bias would be set @ 37 mA for a 70% idle setting
Also you could use a .65 multiplier if you like. I prefer the 60% setting.
With a 6550 of KT88 I would use a 30W multiplier.
 
So nobody knows anything about this "special" biasing or variable ac effect the i take it? I know the formula for biasing.
 
I think its just marketing BS...

I can't recall exactly but I think it was Dave Friedman who serviced Eddie's amps, and he said that Ed biased his around 30. The service manual says 20. Fender will likely just tell you they can't recommend anything other than what is in the service manual.

I'd be interested to hear what they say if you contacted them directly for support on the issue with that question about the "special" biasing and transformers.
 
:scared: Yeah man, I sent them an email with no response. Probably just BS
 
Mine (100w) came from the factory at 15ma as well....I didn't pay any attention to whatever people (or a manual) were saying about where it should be, just trusted my ears - the two most important things that audibly enhanced the amps tone for me was kicking the bias up to around 28-30ma and also micg'ing (when recording it) a v30 (helped tamed some subtle high end fizz IMO). FUN amps! Slap an MXR 10 band in the loop to further shape its tones.
 
Hate to resurface this thread but where On the 5150 iii can yOu bias the amp?
 
Jeff-tranchina":dgipt514 said:
Hate to resurface this thread but where On the 5150 iii can yOu bias the amp?
Click to expand...
The bias adjustment is under the chassis. You have to take the amp out of the head shell to do it. I had mine modded so it is on top of the chassis now. :thumbsup:
 
Here.
http://sites.google.com/site/jimificati ... schematics

test points TP36
bias adjust TP6

The head Fender EVH engineer told me that biasing it to 30mA is fine, current models are at 30. Early models were biased at 20, he didn't really know why.

This is for the 100w.

May want to save the link. Click on the pics and they will shrink to size.

I'll reset the bias mine eventually.

Good luck/be careful and let us know how it turns out.
 
Laura":10y1dc54 said:
Jeff-tranchina":10y1dc54 said:
Hate to resurface this thread but where On the 5150 iii can yOu bias the amp?
Click to expand...
The bias adjustment is under the chassis. You have to take the amp out of the head shell to do it. I had mine modded so it is on top of the chassis now. :thumbsup:
Click to expand...

hate to sound like a noob but how do you take the chassis out? does it just slide out or are their screws underneath ?
 
Joe-TX":2h3jmhy7 said:
Here.
http://sites.google.com/site/jimificati ... schematics

test points TP36
bias adjust TP6

The head Fender EVH engineer told me that biasing it to 30mA is fine, current models are at 30. Early models were biased at 20, he didn't really know why.

This is for the 100w.

May want to save the link. Click on the pics and they will shrink to size.

I'll reset the bias mine eventually.

Good luck/be careful and let us know how it turns out.
Click to expand...

Alright thanks i appreciate all the help! Ill try and figure it out later on today and will post back!
 
Whoops.... one more thing. Actually two haha... Does anyone happen to know what stock tubes were in the 5150 iii? I bought it used and I know it takes 6l6 as the power tubes and 12AX7a as the preamp tubes but what brand? And if I put different tubes in do they have to be biased differently? And second, whenever i turn on my amp, without anything plugged in, all the channels make a really noticable like humming noise. It almost sounds like waves or a helicopter on every channel. Could that be from in not being biased properly? Or could the tubes be bad?

This is my first tube amp so sorry for sounding like an idiot hahaha
 
My early version had all EH/Sovtek including the preamp tubes.

Current models have JJ's in the power section. Not sure about the 12ax7 pre's though.

If I were to retube today I'd probably go JJ's just cuz thats what they are using but someone here may suggest another brand that they have experience with.

Can't help you with the humming noise... never heard that before. Sorry.
 
You must log in or register to reply here.
Back
Top