Demeter Amplification VTHF-275 User manual

VTHF-275 Power Amplier User’s Guide
Congratulations on your purchase of the VTHF-275, one of the nest sounding all tube ampliers
in the world today. To insure that your unit provides you many years of listening pleasure please
follow the directions included in this guide.
USER ADJUSTMENTS
Bias Controls: each output tube has it’s own bias adjustment. Properly adjusted bias insures
lower distortion and noise and insures a longer tube life. Although the bias is adjusted at the
factory, tubes will age differently over time and will need adjustment to insure optimum per-
formance. The bias should be adjusted when you rst use your amplier, a week later, and month-
ly after that. This will insure long tube life (allow 15 minute warm up time before adjusting).
Procedure
1. Connect your amplier to the proper speaker load.
2. Turn on the amplier and let it warm up for 15 minuets.
3. Connect voltage meter to the amplier by connecting the black lead to the black ground input.
Then connect the red lead to tube 1 red input connector.
4. Set your voltage meter to millivolt scale (MV) and adjust the trim pot with a small at head
screw driver until you read 300 millivolts plus or minus 5 millivolts. In some meters this will
read .300 volts.
5. Repeat steps 3 and 4 for tubes 2 through 4.
Feedback Control: Turning up and down the feedback on the amplier affects the sound in a
number of ways. With the feedback on high the sound is tighter and the distortion and gain are
lower. The feedback set lower will increase the gain and make the sound smooth and loose. Set
the feedback control to suit your own listening preferences.
GENERAL INSTRUCTIONS
1. Make sure your speakers are connected to the proper impedance speaker terminal 8 or 4
ohms. If your speaker is a different impedance, connect to the one closest to your speaker’s
impedance.
2. Make sure your volumes are adjusted for the proper stereo perspective.
3. If you hear hum coming from your speakers you may have a ground loop and have to lift
grounds to eliminate the problems. Consult your dealer for the solution if this occurs.
4. If the amplier is used in a bi amp situation and is used to operate high frequencies the feed
back should be set on low and 40 ohm 20 watt resistor needs to be attached to ground and the
8 ohm tap.
5. WARNING: Tube ampliers need to see a load to operate. Please make sure speakers are con-
nected before turning amplier on. Failure to do so will result in damage to the output trans-
former and void your warranty.
6900 Kingsbury Road | Templeton, CA 93465 | 805-461-4100 | http://www.demeteramps.com/

VTHF-275 Power Amplier User’s Guide
OUTPUT TUBE SELECTION AND INTERNAL ADJUSTMENT
The output tubes on your amplier have been carefully selected and matched for your amplier.
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 Amplication 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 amplier from mains. Hook up meter to bias adjustment terminals (ground and
tube one). Set bias controls to mid position. Carefully turn the amplier over and remove the
bottom cover. Plug the amplier in. Turn the amplier 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 amplier and wait
5 minutes. Replace the bottom cover and turn the amplier back over. Adjust the bias for each
tube as previously shown.
6900 Kingsbury Road | Templeton, CA 93465 | 805-461-4100 | http://www.demeteramps.com/