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.

Westinghouse