Bias problem

  • Thread starter Thread starter splawner
  • Start date Start date
splawner

splawner

Well-known member
I have a modded Marshall style amp. I’m having a problem with the bias. 50 watt. The one tube is biasing much hotter than the other. I’ve tried with multiple sets of power tubes that are matched. The one is biased at 40mm and the other only goes to 24mm...any ideal what can fix this problem?
 
Check your bias spitters, likely 220k resistors. Start of making sure they are in spec
 
Check your coupling caps fro leakage from the phase inverter stages to the grids of the power tubes. If they are leaking DC they’ll throw off your negative grid bias and cause your tubes to either runaway bias or bias extremely warm. You’ll get the problem especially if you’re building a kit amp with NOS stuff from the old ages.
 
@splawner how did you make out with your bias issue?
 
Good to know what the issue was and some of the symptoms/effects that a bad screen grid resister can cause.
It would not bias at all. Was not getting a reading on the meter....and tube was not getting real hot.
 
Back
Top