Bias Question

  • Thread starter Thread starter Ampaddict
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Ampaddict

Ampaddict

Well-known member
Hi Guys!
I have an old '85 (or so) Demeter TGA-3. It runs 5881's.

On my Bias Rite w/ the Plate Voltage of 500 (!) the highest I can get the BIAS up too (cranked) is around 20mA on the tubes. (17 mA and 19mA on Sovtek 5881's)

Is it okay to leave the bias cranked up all the way? :confused: I mean according to the Weber Bias Calculator it should be up to 36 mA. :confused:
 
i have, but don't have a clue if it's allright or not. and was never happy with the sound of them not being biased right.


i've got set of Gold lion KT-77's that won't bias up it anything i've got, intended to get Tube Depot to take them back but was too busy at the time to screw with it, and now it's been months.


if they're new, i'd try and make whoever you got them from take them back.
 
Thanks- they are old tubes, it seems the amp bias adjust itself is to blame. Almost seems to be in the 6V6 range.... :confused:
 
If the amp is meant to run on 6L6 then you should just be able to adjust the resistor that is connected to the bias trim pot, if there is one. By adjust, I mean replace with one of a lesser value. Like if it's 47k, try a 27k or something. Or if you order tubes from Groove Tubes, you can get tubes that break up sooner, which would be like rated at 2 on the 1 to 10 rating they give and those should bias up higher. Get the schematic for your amp at schematicheaven.com or dot whatever it is and find your bias resistor, it's pretty easy to do, just be careful not to burn the pcb.

http://schematicheaven.com
 
wow, didnt see your amp on there but Im sure if you posted some chassis shots of the amp, someone could help you get your bias up. Definitely not gonna sound good at 20ma.
 
Loudness250":4yqn01bx said:
wow, didnt see your amp on there but Im sure if you posted some chassis shots of the amp, someone could help you get your bias up. Definitely not gonna sound good at 20ma.
Click to expand...

It actually still sounds great. I think I need new tubes. These might even be the original tubes! :lol: :LOL:
 
You need a hotter set of tubes than those. I think those amps can run 6550's as well.
 
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