Well, with 80 views and no responses...I finally emailed EvaAnna....as usual she responded immediately with her usual quick wit.....and said . . . You should ask your "ace" technician what he did. I know she knows the answer... I asked my technician but he is Korean- American with a very heavy accent...I could not understand him. Oh well.
Bias Setting for Older VTL 75/75
I have a very early VTL 75/75 and I think it may have a 5 ohm cathode resistor between pin 1 and pin 8. After adding a bias circuit, my ace technician told me he set the bias for the output tubes at 280 mVolts like my other newer VTL amps MB80s and Compact 100s. When I got the 75/75 amp home I tested the current draw with one of the digital meters found on ebay (which has worked extremely well on other amps) and it read 45 mAmps???(versus 28) with new EH KT88s. I put in some US Philips 6550s and the current draw was 60! mAmps. Then I put in some old US Tungsol grey plates no holes and they read 30 mAmps?? Should my Technician have set the bias at 125-150 mVolts with the 5 ohm cathode resistor?? and why do the different brands differ in current draw so much?? Any comments would be greatly appreciated. Emailing VTL is a waste of time and I do not want to bother Eva Manley again.
Thanks, Larry
Thanks, Larry