Tubes Asylum

RE: Bias question

63.247.1.2

FenderLover

In Reply to: RE: Bias question posted by Tubers on January 08, 2012 at 21:35:19

Well, I'll assume the battery is ok in your DVM. If the amp has a one-ohm dropping resistor from cathode to ground 0.035 to 0.05 volts would be more reasonable (depending on tube type and plate voltage).

If the amp has a 10-ohm resistor between cathode and ground. Then, 0.35 -0.5 volts maybe more appropriate.

What kinda amp do you have?

Follow Ups:

RE: Bias question - Tubers 22:46:48 01/08/12 (3)
Image Audio (China) 34i integrated which accepts EL-34, KT-66 or 6L6GC tubes.

Tried to upload the pic, but it does not work.
- RE: Bias question - FenderLover 01:52:17 01/09/12 (2)
  Have you tried writing to their tech support? And how does the amp sound with the bias reading 0.035 volts?
  - RE: Bias question - tubers 05:49:35 01/09/12 (1)
    I wrote the seller but haven't received a response. I will write to the manufacturer now (if he understands me).
    
    I did not stip at 0.035 volts, I set the bias at 0.35. Sounds good - I liked it better than with xf2-coded Mullard EL-34.
    - RE: Bias question - FenderLover 07:13:40 01/10/12 (0)
      Sounds like you answered your question. To be extra sure you can use a Bias Probe or some such aftermarket device and measure the mV across the cathode to ground. Then, measure the anode plate voltage and see if the resulting idle wattage is within range of the spec's of the tube.
      
      mV (measured, using these devices which usually have one-ohm resistors) = mA, at idle (no volume, speakers connected). One mA = 0.01 amp. Amps TIMES plate voltage approximates the idle wattage.
      
      Be sure that your tubes are not red plating. Or running so hot, as to distort at lower volume levels, than usual.

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