VTHF-275 Power Amplifier User’s Guide
Congratulations on your purchase of the VTHF-275, one of the finest sounding all tube amplifiers
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 first use your amplifier, 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 amplifier to the proper speaker load.
2. Turn on the amplifier and let it warm up for 15 minuets.
3. Connect voltage meter to the amplifier 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 flat 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 amplifier 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 amplifier 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 amplifiers need to see a load to operate. Please make sure speakers are con
-
nected before turning amplifier 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/
