[Amps] Eimac AS-47 2m 8877 amp?

Carl km1h at jeremy.mv.com
Fri Jan 18 16:05:50 EST 2013

I built a split flat plate design using a 3CX1000A7 almost 30 years ago and 
still use it; the same tube easily does 1500W out with 100W drive from a 
modified 180W brick driven by an ancient MM-144 transverter.

The tubes can be found and sockets are very scarce (some have modified the 
4CX1000 socket); however the tube is indestructible, instant on and a rugged 
45W grid. It was a scrapped TV translator pull when I got it with the socket 
at a lot less than a 8877; $100 if I remember.

Eimac rates it at 1500W Pd in GG AB2 at up to 3500V.

Unlike most 2M designs I went a slightly different path and used a small 
vacuum variable ror Tune and no Load variable. The output is silver soldered 
directly to the flat plate after finding the sweet spot.  Efficiency is 
around 63% at 3KV.  Tuning has never drifted even in contests or as an AM 


----- Original Message ----- 
From: "jeff millar" <wa1hco at wa1hco.net>
To: <amps at contesting.com>
Sent: Friday, January 18, 2013 2:08 AM
Subject: Re: [Amps] Eimac AS-47 2m 8877 amp?

> Used one for years for our VHF Contest group and rebuilt it several times.
> C5 is a flat copper plate about 10 cm wide and 5 tall.  It has flexible 
> brass sheet on each end that wraps back to ground to the aluminum box. 
> The brass is U shaped and acts as a spring to suspend the flat plate.  The 
> tube has a copper ring that connects to the anode lines and has another 
> flat sheet of copper soldered to it to make the plate.
> I glued teflon sheet (treated to make it glue-able) to the tune and load 
> plates to avoid dramatic events if the tuning every got too aggressive.
> Look at http://www.qsl.net/dl4mea/2g35.htm for a similar design using a 
> GS35.
> Also look at http://www.nd2x.net/base-1.html for a bunch of designs.
> jeff, wa1hco
> On 01/17/2013 05:40 AM, PY1NB - Felipe Ceglia wrote:
>> Hello,
>> Has anyone here ever built such an amp?
>> I'd like to see pictures of its internals, if possible.
>> I am not sure how C5 connects to ground, seems like the brass tube would
>> fit and move directly to a hole in the aluminum chassis?
>> Here is an AS-47 reprint: http://6mt.com/wpo2kwamp.htm
>> 73,
>> Felipe Ceglia - PY1NB
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