Somewhere I have a very unusual 8877. It has no fins. It came in a surplus
pulsed RF amplifier used in a MRI system. The anode fit directly into the
tuned plate line (pipe) and some air was blown down the line to provide a
cooling. It was around 200 MHz and used in a high resolution imaging animal
research lab. They scrapped the whole system but traded in the
superconducting magnets. I called EIMAC and gave them the House number on
the tube and sure enough it was simply a 8877 without any fins custom
produced for the NMR folks.
73
Bill wa4lav
At 10:14 AM 2/6/2007 -0500, Paul Christensen wrote:
> > "A very good friend and my elmer has an Alpha PA-70V and he needs to
> > replace the famous and almost disappear 3CV1500A7. Does anyone knows where
> > we could find one or how this amps can be modify to accept another
> > available vacuum tube?"
>
>Juan,
>
>The few new tubes that exist are locked up in our safe-deposit boxes. The
>3CV1500A7 is electrically and in most respects, identical to the 3CX1000A7.
>The only difference is that the CV has a boiler fitted onto the anode for
>vapor cooling. But the socket, and all other physical and electrical
>properties are the same.
>
>There are several possibilities:
>
>1) Send the tube to Econco for a rebuild estimate. In speaking with
>Econco's John Cavenary a few years ago, the success rate of a rebuild is
>less than 50%. The tube structure of that small power tube just does not
>hold up well to the forces required in the rebuild process. Econco should
>be consulted first before sending them the tube. Their policy may have
>changed since the last time I spoke with them;
>
>2) Modify the amp with a 3CX1000A7 and add air cooling. This involves
>extensive metal work, but many 70V amps were converted by the Alpha factory
>and their customers back in the mid '70s. "Instant-On" feature is
>maintained; or
>
>3) Modify the amp with an 8877. Same air cooling caveats apply, only a
>time-delay system will need to be incorporated. Not too terribly difficult,
>but challenging for some. "Instant-On feature is lost." Before Bob
>Douglas, W5GEL became SK a couple years ago, he modified his 70V with the
>8877 and we was very pleased with the results. And, he did the mod at near
>90 years of age.
>
>I just recently purged the H2O system on my amp and it's as strong and
>silent as ever. Quick horror story: I purchased a gallon of "Brand X"
>distilled water while standing in line at the local Walgreens. Purged the
>water and added the Brand X water. Powered-up and Leakage current went
>off-scale. Either I got a bad jug or that company is re-selling tap water
>as "distilled." Purged the amp again three times and added ZephyrHills
>brand and leakage current was back to zero!
>
>FYI - for those interested in what the inside of a vapor-phase-cooled amp
>looks like, pictures of my 70V can be seen on Alpha's web site.
>
>http://www.alpharadioproducts.com/html/70v_pix.htm
>
>Paul, W9AC
>
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