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7868 Tube List
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.
||RCA Black Plate USA New
(NOS) Earlier version of this tube made by RCA had black
plates. Where all 7868's are in short supply, these black plates
are especially hard to find
||As Above, but USED TESTED GOOD
|| RCA Gray Plate USA New (NOS) Later
production RCA's had gray color plates. Otherwise, they are the
same as the earlier black plate version.
Sylvania USA New
(NOS) Sylvania made an excellent
7868. Many 7868's were made by them. They had the exhaust
tip on the top of the tube unlike GE and RCA that had the tip on the
bottom (between the pins). This makes them look very cool.
General Electric USA New
(NOS) GE's look a lot like RCA's with
gray plates. Exhaust tip is on the bottom like RCA.
GE, or Sylvania USED TESTED GOOD