VTPH-2 Vacuum Tube Phono Preamplifier Owners Manual
14
Care needs to be taken during this
procedure in order to prevent
damage by static electricity to the
VTPH-2 internal components.
The original tubes should provide
many years of good performance,
due to the conservative plate volt-
age and current operating require-
ments of the Herron Audio Phono
Preamplifier.
If tube replacement is required,
channel-to-channel gain matching
can be done using the left and right
gain controls on the printed circuit
board.
Tube Recommendations
Left channel tubes are V1 and V2
Right channel tubes are V3 and V4
Output tube (for both channels)
is V5
Units RIAA passively compensated
for 4 3 12AX7s, and 1 3 12AT7,
the following tubes are
recommended:
V1 and V3 (first gain stage) 12AX7
V2 and V4 (2nd gain stage)
12AX7
V5 (output stage) 12AT7
Units RIAA passively compensated for
2 3 12AX7s, and 3 3 12AT7s, the
following tubes are recommended:
V1 and V3 (first gain stage) 12AX7
V2 and V4 (2nd gain stage) 12AT7
V5 (output stage) 12AT7
Other current production or NOS
tubes may be preferred with
experimentation.
Changing Tubes
When changing tubes, the phono stage should be unplugged
and left off for a minimum of 30 minutes prior to opening the
unit, to insure that hazardous voltages in the power supply have
time to discharge before entering the unit.
CAUTION
Tube Locations
Front panel
Back of unit
Tube locations V1 to V5 are as
marked on the printed circuit
board.
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