Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Karl -
The only source I know of for "matched" sets of three is RF Parts. They
charge around $90 / set.
Generally speaking, three NEW tubes of the same manufacturer are matched
closely enough. Drake "matched" them by measuring the plate current
they drew in the transmitter at a fixed grid bias voltage and then
grouping them. You can check by putting them in the transmitter,
keying it by PTT with GAIN full CCW, and measuring the voltage across
each cathode resistor. For maximum accuracy, measure the value of each
of the three cathode resistors (they should be 15 ohms +/- 10% and
ideally within 5% of each other) and then calculate the current. If one
tube is drawing more than 5% more or less than the other, it would be
best to find another.
Ideally, each tube should draw exactly 1/3 of the total cathode current
at idle, and the assumption (questionable) is that they will equally
share at full current as well.
All that being said, transmitters have been run successfully with three
tubes from three different manufacturers and work for years.
Mismatching of tubes CAN result in increased IM distortion, primarily a
result of one tube taking considerably more of the load than the
other(s), but _usually_ shows only by measurement, not sound!
Mismatched tube brands also CAN cause difficulties with neutralization,
usually presenting as "will neutralize on one band but then not
neutralized on another".
73, Garey - K4OAH
Atlanta
Drake C-Line Service Manual
<http://hr99.home.mindspring.com/R-4C_Servicez/>
Karl Corder wrote:
I would really appreciate to know where I can obtain these tubes.
Thank you very much, the helpfull knowledge and information passed on this
site is really appreciated. -Karl WA2OVJ
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