[AMPS] 3cx800a7 response from Eimac

[Tom Hix W4TH]

There has been some talk on the reflector lately about Eimac having
stopped production of the 3cx800a7 tube, and having replaced the tube
with the 3cpx800a7. I wrote to Eimac, and here is the reply I received. 
73
Tom
W4TH
+++++++++++++++++++++++++++++++Tom, 
Your inquiry has been forwarded to me, and we do appreciate the
opportunity to answer your questions directly. 
The 3CX800A7 is still in production and will continue to be. As with any
tube from any manufacturer, there are occasional variations which result
in "super tubes", but all the tubes we ship meet spec or they don't go
out. We do sometimes have products returned due to failure under
warranty, and we cover these. Although our failure rate is low, I am
sure that it seems high to the individual who has had a failure in the
only one he has received. Some equipment may have been set up so that it
only works with super tubes, and then when more standard tubes are
received there are problems. While it would be nice if Eimac produced
only super tubes, that is unfortunately not always possible. 
The 3CPX800A7 is a drop-in substitute for the 3CX800A7, both
mechanically and from a tuning standpoint. It has a slightly longer
ceramic and will hold off higher plate voltages, but it is otherwise the
same. We have found that in FM transmitters operating in class AB, the
plate voltage can be raised to 3.2kV, which provides a slight gain
improvement and makes the tube easier to drive. This seems to be
effective in those applications where the equipment was designed around
really hot tubes, and it is also effective in providing additional
margin for equipment operating in parts of the world where the line
voltage sags significantly. For these reasons, Eimac now recommends the
3CPX800A7 for FM transmitters putting out more than 800W. 
Both the 3CX800A7 and the 3CPX800A7 are in production, and are available
from stock at Richardson Electronics. 
I hope this covers your questions.
Best regards, 
John Allan
Vice President of Marketing
CPI / Eimac


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