Electronics > RF, Microwave, Ham Radio

Need help identifying tube

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I am trying to identify a tube, in particular, if there is now a source of such a tube from China or Russia as these are likely not made anymore in the USA.

The tube is from a 10 kHz - 250 MHz, 2500 W Amplifier Research Model 2500L MII amplifier. It is one of eighteen tubes in the amplifier finals. The tubes are oil cooled as can be seen by the nipples on the top. The amplifier itself dates from the early 1990s.

The tube is marked

"Amplifier Research"
1003787 - 101C

I have also included the schematic. I was not able to find the item in the BOM corresponding to these tubes however.

Are any similar tubes used in amateur or broadcast amplifiers?


Have a look at this site.
And this one.
It could be 4cx250 with some kind of liquid cooling device.

Wallace Gasiewicz:
I agree probably a 250 or even a 350.
Does not look like the "cooler" can be easily removed, for a look at the tube itself

There are several linears that use these tubes but a lot of them have too much amplification to meet the FCC standard for ham amplifiers
I have an old military radio that uses two 250 or 350 tubes in the final (depends on the model)

Licensed amateurs can build or modify amplifiers "without concern for the certification rules" that manufacturers and dealers have to follow. Such non certified amplifiers can also be resold by dealers but only to licensed amateurs.
Reference: Extra Class License Manual section 3.6 and exam questions E1f03 and E1f12

However operation still has to be within all of the  license class, output power and spurious  emission limits applicable to the band and mode.

Edit Above is for USA, .Other countries may differ.


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Does seem to be a conduction cooled variant.

Also, holy shit, splitter into matched delay lines into 6x grid lines each, all feeding one common plate line in order?  Amazing; that thing must've been a terrific pain to tune (or design)!



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