In this scenario, a tube can “
feed back
”, or give off a loud, high pitched squealing noise.
Feed back can occur intermittently, even without an instrument plugged into the input of the
amp. This does not mean that the tube
(s)
are completely unusable. One possible solution you
can experiment with is reversing V1 to the V2 phase inverter socket where microphonics are
not as noticeable. The V2 position 12AX7 may be quieter in the V1 position.
Please note:
a small amount of “
hiss
“ is normal for high gain amplifiers. An excessive
amount of hiss, especially when the volume control of the amplifier is all the way down and
with no instrument plugged in the amplifier’s input, usually denotes a bad pre amp tube.
Some n.o.s. audio tube suppliers offer “
select
“, or hand picked pre amp tubes, which are
superior in all aspects of quality, especially when it comes to being quiet and non-
microphonic.
Please pay close attention
when extracting and installing the power and pre amp tubes. The
pins
must align perfectly
into the tube’s socket. Bent pins, especially when forced into a
tube socket, can cause serious damage to an amplifier’s tube socket pin inserts. This results
99%
of the time with the tube socket needing replacement. To avoid this contingency, we
recommend that you purchase a miniature pinned, nine holed, pre amp tube pin straightener.
These can be found on line from many vintage tube retailers. This easy to use device
guarantees that your pre amp tube and 6BQ5 / EL 84 power tube pins will be straight and
aligned for socket insertion.
NOTE:
Komet
Amplification’s Warranty
will not
cover damage done to a tube socket’s
insertion pins from forced or accidental mis-alignment / and or bent / crimped insertion pins.
BIASING THE KOMET
SONGWRITER
The Komet
Songwriter
is a cathode biased amplifier
( no bias adjustment should be necessary
)
. An internal resistor sets the amplifier’s power tube bias. To guarantee your amplifier will
operate properly in conjunction with the supplied voltages and current draw of the Komet
Songwriter
, we recommend that when you replace your
power tubes
, that you purchase a
matched
set of
EL 84 / 6BQ5
s
with a low
IP
( or a low current draw )
grade / configuration.
Most reliable and reputable audio tube vendors and
n.o.s.
tube dealers sell their
power tubes
in matched, output power or current draw - numerically rated - sets.
You should be able to request a certain IP grade or range from your tube vendor.
Some
examples:
the Sovtek / New Sensor EL 84 grade for the Songwriter
is an IP number range
from
# 12
through #
18
. The Groove Tube scale for the Songwriter
is a grade
# 1
through
#
3
.
Note:
the 12AX7
pre amp
tubes in your amplifier are internally self biased and need no
adjustment.
Copyright 2000-2012, Riverfront Music, L.L.C. d.b.a. Komet
Amplification. May not be reproduced in any form without express written
consent from Riverfront Music, L.L.C. d.b.a. Komet
Amplification.
