D.W. Fearn VT-1, Operating Instructions Manual, Page: 36 / 40

D.W. FEARN
VT-1 & VT-2 Microphone Preamplifers
36
and grade them according to noise, microphonic response, distortion, and other character-
istics. A low-noise tube from us will meet the original VT-2 specifications.
The base pins of vacuum tubes supplied by D.W. Fearn have been chemically treated for low
contact resistance and oxidation prevention. When handling these tubes, care should be
taken to avoid removing or contaminating the treatment. Use a lint-free cloth or paper towel
to avoid direct contact between any part of the tube and your fingers.
Remember that vacuum tubes may be quite hot during operation. Protect your fingers dur-
ing tube replacement. The VT-2 should be turned off before removing tubes. Allow at least
one minute for the filter capacitors to discharge before tube removal or insertion.
Tubes are made of glass and will break if dropped or even bumped in a critical area. Handle
with care.
Electrolytic Capacitors
The VT-2 is designed and built to last for a long, long time, and it is possible that some com-
ponents (e.g. electrolytic capacitors) may reach the end of their life long before the equip-
ment becomes obsolete. The electrolytic capacitors used in the VT-2 typically will last at least
twenty years. If there is a measurable and/or audible increase in 120 cps noise, the filter
capacitors should be suspected. They should be replaced with new capacitors of equivalent
capacitance and voltage rating, and the replacements should be specified for a minimum ten-
year service life.
Electrolytic capacitors are also used as plate and cathode decouplers. In choosing a replace-
ment, the same considerations as with the filter capacitors should be followed.
Rotary Switches
The rotary switches in the VT-2 were chosen for their self-cleaning property. In a clean envi-
ronment (non-smoking, with frequent room and equipment vacuum cleaning), and with reg-
ular use, the rotary switches should require little attention for years. Audio is not switched in
the rotary switch itself -- the switches only control gold-contact relays. But if cleaning
becomes necessary (as evidenced by intermittent relay switching), we recommend using De-
Oxit (Caig Laboratories). Follow the instructions provided with the product.
If the switches are not used regularly, oxide and dirt can build up on the contacts. Rotate the
switches through their range a few times on a weekly basis to keep them clean.
The toggle switches should never require cleaning.