[BC] 5CX1500 Tubes - Recollection

[John Lyles]

I'll toss in my 2 cents too. I was about to send the text of the Eimac application bulletin that was released about that time (in the 1980s?) 
that summarizes what Reid Brandon said in his note. Lightly loaded amplifier means higher loaded Q, and higher reactive current in the capacitance of
the plate to screen electrodes. This is of course driven by higher plate voltage which has a larger peak swing. So, loading it heavy would reduce the plate swing, still getting the power out with 
a lower plate resistance for the circuit to match to. This problem is worsened at VHF, as the reactive Z of the capacitances is much lower than at MW. 

My experience with the old Collins 2.5 kW using the pentode and 310 exciter was in the late 1970s, where I had to maintain one in VA that was hammered by lightning. The big SCRs 
in the primary 220 VAC line were messed with, and so was the controller board (burned traces). Somehow I managed to float an oscilloscope off ground (scary) and probe the SCR gate drive while it was running. 
Don't touch that scope! Every so often, it would jump (the phasing of the pulse) and the circuit breaker would pop open. GM was not excited about buying all new parts from Collins, so we had to do a lot of piece meal parts replacement which took 
a lot longer and was a band aid. I was happy to leave that station, although I liked working on the BC1G. 
John Lyles

> Message: 4
> From: "Schardin, Hal (DEED)" <hal.schardin at state.mn.us>
> 
> 
> I recall the tuning difference between the A and B version tubes in an FM transmitter I used to maintain. I also recall the mention of ceramic seal issue.
> Here's an interesting response from an Eimac  engineer on the differences of the A version vs the B version:
> http://www.ez-net.com/~alankilgore/Misc/5CX1500_Tube.htm
> 
> Hal Schardin