VTHF-275 Power Amplifier User’s Guide
OUTPUT TUBE SELECTION AND INTERNAL ADJUSTMENT
The output tubes on your amplifier have been carefully selected and matched for your amplifier.
When replacing tubes or if you have a tube that fails or goes out of the adjustment range you
can order either a replacement set of tubes or a single tube by calling your distributor or Deme
-
ter Amplification for an exact replacement.
If you cannot do this and the tubes you buy fall out of the adjustment range of the front panel
controls there is an internal master bias adjustment. WARNING: THIS SHOULD BE PERFORMED
ONLY BY QUALIFIED SERVICE PERSONAL. THERE ARE 600 VOLTS DC PRESENT AND INJURY OR
DEATH COULD OCCUR!
Procedure: unplug amplifier from mains. Hook up meter to bias adjustment terminals (ground and
tube one). Set bias controls to mid position. Carefully turn the amplifier over and remove the
bottom cover. Plug the amplifier in. Turn the amplifier on with the proper speaker load attached.
Let it warm up for two minutes. Very carefully adjust the trim pot found on the power supply
board until the meter reads approximately 300 millivolts (.300V). Unplug the amplifier and wait
5 minutes. Replace the bottom cover and turn the amplifier back over. Adjust the bias for each
tube as previously shown.
6900 Kingsbury Road | Templeton, CA 93465 | 805-461-4100 | http://www.demeteramps.com/
