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Matching Tubes
Tube matching is required when 2 or more tubes are
operated in push-pull in an output circuit. This is
especially important when the circuit is a fixed bias circuit and
the tubes are operated at or even a little beyond their maximum
ratings. This is typical in audio amplifiers as
manufacturers would try to squeeze every watt of power out of the
amplifier. If you don't use reasonably matched tubes in such
a circuit, you run the risk of destroying one or both tubes as you
could never properly bias the circuit for both tubes. They
don't usually have to be EXACTLY matched; just within a few
percentage points of one another. Also, if you have a stereo
amplifier which run the tubes in 2 pairs, IT IS NOT NECESSARY TO
BUY A MATCHED QUAD! 2 matched pairs will be fine. Tube
tester matching is NOT normally effective matching because most
tube testers operate the tube far below the normal operating
parameters used in the amplifier. Tubes that match at
typical tube tester voltages will NOT usually be matched in the
amplifier. I use different types of test equipment to match
tubes. I normally operate the tubes at typical amplifier
voltages and measure plate current. Transconductance is NOT
important when matching this way.
Matching is available when I have enough tubes on
hand to select from. Plate current
matching where available will add an additional $5 per tube.
Please inquire about matching for NOS and used tubes.
Matching is usually available on currently produced tubes like
Russian tubes. |
