[NLRS] [Fwd: [VHFtubeamps] Need some help with a tube cross-ref]

[Dr. Gerald N. Johnson]

On Thu, 2006-09-07 at 03:19 +0000, Scott wrote:
> 
> Maybe someone can help out?
> 
> 
> 
> -------- Original Message --------
> Subject: [VHFtubeamps] Need some help with a tube cross-ref
> Date: Wed, 6 Sep 2006 21:38:48 -0500
> From: Jim Strohm <jstrohm at ev1.net>
> Reply-To: VHFtubeamps at yahoogroups.com
> 
> These shining dragon's teeth showed up in my latest ebay acquisition.
> 
> Eimac Y-739A, three each
> 
> I have been able to learn that they are coaxial-base microwave planar
> triodes, air-cooled, and are similar to a CPI 8940.  They look like
> about 200 - 300 watts CW and from what little I've been able to find,
> full rating power would be around 1200 MHz.  The chassis was marked
> "20kW Microwave Transmitter" and based on the size of the power
> supply and some other markings, these would be the right size for a
> pulse microwave RF generator of that power range.
> 
> I'm looking for a data sheet, ideally.  I can reverse-engineer
> voltages from the chassis they came out of, but data sheets make it
> easier, especially if they include a test circuit.
> 
> I have three of these with sockets and individual filament  and grid
> regulator supplies, and they look new -- but the chassis has almost
> 1300 hours on the hour meter.  These look like they've never seen use
> -- none of the usual scorched dust marks on them.  I'm thinking that
> one would be a whopping better tube than a 2C39 for use on 1296, and
> while it would not work in the same socket or cavity, might almost
> work on the same voltages.
> 
> Email or post here, please.
> 
> Jim N6OTQ
> 
Have you tried asking CPI/Eimac? They invite that on their web page
where the show only the most popular tubes. But invite asking about
others by going to http://www.cpii.com/eimac/rueck/feedbackform.aspx
or calling "1-800-414-TUBE and select choice number 1."

In the history of Eimac that I've seen, Y prefixed tubes tend to be
variations or new devices and the part number tends to be short lived.
Either its given up as a bad idea (insufficient sales) or it gets an
Eimac style or JEDEC number assigned.

At least in the old days, Eimac was nearly all hams so was quite willing
to help hams with information.

I've checked my Eimac catalogs but not my data book (because its not
been updated since 1968) and found no Y-739. I found a cavity for a
Y-798, which is a specially processed 8938 for pulse. Very likely the
Y-739A was also a specially processed tube with better vacuum and maybe
better insulators for the pulse rating.
-- 
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer