>Einar Persson wrote:
>
>> Why has the 3CX3000 became so popular?
>
>It is a stable tube, easy to use, rebuildable, available surplus, easy
>to mount, and very very clean.
>
>> Why not use the 4CX3000 instead?
>
>It requires a socket, bias and screen supply, and often more expensive.
>At times it is less expensive to build a small IPA stage than to build
>a PROPERLY limited and regulated screen supply.
A diagram of an RF-proof, short circuit proof, easy to buile, 723-based
screen supply that can provide up to 2kV of adjustable, regulated,
current-limited screen V is available at
http://www.vcnet.com/measures.
By adding FET pass transistors, the regulator can handle 2A for 8973
users.
I agree with Mr. Rauch about the expense of the 8169's unique socket.
The new price IS WAY over the top and used ones are scarce. [W6TG
(w6tg@aol.com) has 1 for sale]
IMO, a better socket choice is the much more common Eimac SK-300A socket
A wide range of tetrodes fit the SK-300A socket. Obsolete SK-300
sockets can be purchased for even less money. However, it takes a coping
saw, a vise, and about 30 minutes to convert an SK-300 to the air-flow
equivalent of an SK-300A.
There is no screen bypass C for the SK-300. In RF amplifier service,
the SK-300's screen collet is directly-grounded to the chassis in 8
places with copper ribbons. A simplified diagram of the grounded-screen
configuration is available at the above URL.
Other advantages of the tetrode version are:
--no 51A filament choke
--no Q of 5 tuned input neworks, which have narrow bandwidth, and which
must be capable of carrying the 3A of RF cathode current. .
--it's not just another ho-hum boring 12db G-G project. My 4x3 does
18.3db, if need be.
Rich---
R. L. Measures, 805-386-3734, AG6K
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