I've thought about doing a similar thing in my 8874 amp with the U7, it seems
like it should work just fine, and the price of the tubes is really great. As
a test I had thought about just creating some sort of socket adapter out of
bread board so I wouldn't have to modify the amps socket. One thing about the
3cx800U7 though is the anode cooler is slightly larger in diameter than the
8874 so you have to keep that in mind in some cases.
Paul,
KG7HF
Date: Thu, 28 Jun 2012 21:19:34 -0400
From: "Carl" <km1h@jeremy.mv.com>
Subject: Re: [Amps] 3CX400U7 in Alpha Linear?
To: "Martin Sole" <hs0zed@csloxinfo.com>, <jerry@tr2.com>, "'amps'"
<amps@contesting.com>
Message-ID: <A2AD225EB3FC46D0A7DBD94B113D98CF@computer1>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original
I use the U7 in a combined pair of surplused Eimac cavities for 903 MHz and
have had no problem finding a pair of NIB spares for $20 each.
Ive thought often about using them should my Alpha 76CA finally wear out the
8874's.
One way would be to make a fingerstock grid contact mounted to the chassis
as the first step after removing the 3 sockets. Properly done thats all that
will be holding the tubes in place....a pressure fit.
If you can find some shorted screen bypass rings for 4CX150/250 or
8072/8121/8122 style tubes or variants of either family you can quickly make
a GG ring by soldering small copper strips between the finger stock and
ground section in several places.
The stock chimneys and exhaust stacks can be reused.
Then attach some copper tubing or HB clips to the heater and cathode
terminals and push on connector for the other heater pin; those will be the
only things below chassis.
Bias voltage "may" need to be changed as it runs 12V at 903 but at HF the
stock value may be OK. At HF its still otherwise rated as an 8874.
Since this will only be going to 10M rocket science isnt needed.
A bit more work than 3CX800's but considering prices and future availability
its an alternative to consider.
Carl
KM1H
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