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Re: Biasing Valve Amp

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In Reply to: Re: Biasing Valve Amp posted by Ken Tan on January 21, 2006 at 04:18:01:

Ken,
Check the link below carefully. This will tell you how to bias the amp.
Pay particular attention to this passage:
The reading on the millimeter should stabilize after a little while and indicate a reading between 250to 300 millivolts (0.250 to 0.300 Volts.) The reading on the millimeter may fluctuate a little due to variations in the AC lines. In general, if there is a change of one volt of AC on your line, the bias measurement could be affected by 10 millivolts. It is not unusual for a 120V rated AC line to vary between 115V and 122 V.
Note: The formula for determining the current draw according to Ohm’s Law is R = V/I, where R is resistance in Ohms, V is voltage in volts, and I is current in amps. Changing the subject of the formula: I = V/R. The current draw for each tube is therefore the voltage reading divided by the resistance measured in Step 3 (either 5 or 10 Ohms, depending on the age of your amplifier). Therefore, to get a result of the required 27 - 30 milliamps the voltage reading should be 270 - 300 millivolts for the 10 Ohm resistance readings, and 125 - 150 millivolts for the 5 Ohms resistance measurements.
In other words, depending on the age of your amp, you will either set the bias to .25 to .30 VDC or .125 to .15 VDC. If you havent changed anything yet, you may want to see where your bias is currently set. If. say, your bias is a shade above .30 VDC, its probably a safe bet to use the higher settings.
I hope this helps.
Nels

VTL Factory Bias Instructions (Open in New Window)

Follow Ups:

Re: Biasing Valve Amp - Ken Tan 20:58:40 01/22/06 (2)
Thanks Nels. I find the link very useful indeed. You are really of great help to me. By the way, do you mind if I ask you what amp are you using? Your setup?
Thanks and have a nice day!
Ken
- Re: Biasing Valve Amp - Nels Ferré 23:56:00 01/24/06 (1)
  Ken,
  Glad I could be of assistance.
  My system is undergoing major changes and has been down since November. :( I'm seroiusly jonesing for some tunes, but my new condo wont be completed until lkate next month or possibly early March. My living situation right now is temporary, and cramped, so no room to set anything up.
  TT: SOTA Star/Modded Rega RB-250/Denon DL-110..Dynavector needs retip
  Phono Pre: DIY HiFi Supply Cole Kit (Still in box, hopefully will start this week)
  Pre: DIY HiFi Supply Basie Kit (awaiting upgraded coupling/output caps)
  Amp: Response Audio 3505 (custom JoLida based power amp, 60WPC running KT-88)
  CD: JoLida JD-100 Tube Player, Marantz CDR-630 Recorder
  Tuners: Onkyo T-9 FM..Delphi XM
  Speakers: Infinity Kappa 6.1
  Router Box: Mapletree Audio LR-1 (allows addition of 3 more inputs to Basie, for a total of 7)
  Cables: Alot, various mfgs and DIY
  - Re: Biasing Valve Amp - Ken Tan 06:28:31 01/29/06 (0)
    Neils, congratulation on your new condo/home. Happy for you. You are truely a DIY guy. Unlike you, my set up are all bought ready, mostly used. They are as follows.
    CD - CEC TL51 transport with CEC DAC DX71 MKII and a old Marantz CD94
    Pre amp - ARC SP9 MKII with Philips JAN6922 valves.
    Power amp - Classe CA100 for solid state and VTL80 for valve.
    Speakers - JM lab Mezzo Utopia.
    Cables - Mainly Siltech and Tara Lab Air One.

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