[Amps] Chinese 4CX1000A from Alpha
k2vco.vic at gmail.com
Fri Nov 15 11:33:53 EST 2013
I wasn't entirely happy with the behavior of 4CX1000A pulls, so I decided to
bite the bullet and try a new tube. So much for my 'cheap' amplifier project
(you hot rod guys understand the phenomenon of starting a project because
you already have all the parts and it will cost almost nothing, and then
experiencing 'mission creep')!
Anyway, I decided to order one from Alpha, which sells Chinese tubes that
they have tested and guarantee. There is also a guy on Ebay from Australia
selling new Eimacs for close to the same price when you add the shipping.
The upshot is that the screen current is more stable than with the pulls.
Not surprising, since I understand that many 4CX1000A pulls were removed
from BC service because of excessive secondary emission. The new tube needed
slightly more bias voltage to obtain the rated ZSAC and appears to need more
drive for full output.
Finally, the Chinese version has an anode cooler with internal crimps for
more surface area, similar to the one on the Eimac 4CX1500B.
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