[Amps] 3CV1500A7

[Bill Fuqua]

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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