VTHF-300M Power Amplifier User’s Guide
Congratulations on your purchase of the VTHF-300M, one of the finest sounding all tube ampli
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fiers 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
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formance. The bias should be adjusted when you first use your amplifier, a week later, and month
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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. Remove amplifier controls cover plate on front panel by turning the thumb screws at the ends
of the plate counter-clockwise.
4. Connect voltage meter to the amplifier by connecting the black lead to the black ground input
on the right side of the panel. Then connect the red lead to tube 1 red input connector on the
left side of the panel.
5. 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.
6. Repeat steps 4 and 5 for tubes 2 through 8.
7. Replace cover plate.
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.
Output Mode: this switches the amplifier’s output to either pentode (full power ultralinear
operation) or triode (half power triode operation). Each mode has different sonic attributes: the
pentode mode has more power and dynamic bass, the triode mode has a warmer and more silky
midrange. WARNING: adjust this switch only with the amplifier turned off, the switch noise
could damage your speakers.
Fan: this switch controls the speed of the cooling fan. The fan is optional and only included in
amplifiers specially ordered with this option, as fan noise can disrupt the listening environment.
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