[Amps] 3CX400U7 in Alpha Linear?

[Paul Decker]

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 at jeremy.mv.com>
Subject: Re: [Amps] 3CX400U7 in Alpha Linear?
To: "Martin Sole" <hs0zed at csloxinfo.com>, <jerry at tr2.com>,	"'amps'"
	<amps at contesting.com>
Message-ID: <A2AD225EB3FC46D0A7DBD94B113D98CF at computer1>
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	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