[Amps] Question about an old home-brew amp

[W0UN -- John Brosnahan]

Chris--

Not going to be much help, but HP did build some HF power
amps using the 3CX1000A7 for internal use in some of their
industrial heating processes.  Possibly this is a prototype
and operational on the ISO freq of 13.56 MHz.   Twenty years
ago I had an amp or two from HP that used a 3CX1000A7--but
it has been a long time and I don't recall much about it.

And the "Freyman" MIGHT indicate Bob Freyman, W5VO,
who dealt a lot in surplus equipment both while he was
working at Los Alamos and later when he retired to Longmont,
CO.  He had a store in Longmont for a few years with an
entire basement (2,000-3,000 square feet) absolutely FULL of
electronics equipment and lots of RF stuff.  Unfortunately
Bob passed away a couple of years ago after an extended
illness.

The 3CX1000A7 is an "OK" tube.   Just OK, not great.  It is linear
and will work through the HF and low VHF bands but it has
a power hungry filament (5 volts at 30 amps) and the twist-lock
style socket.

For ham use the 4CX250 is more trouble than it is worth as a
driver since you don't need a driver with the typical 100 watt rig.
Sounds like you have a good start on a home brew amp but you
will have a lot of work to do.  If you can strip the driver out and
if the rest of the layout is conducive to modification to a 20M or
bandswitching amp amp you can go that route.   But since it
was probably designed for 13.56 MHz the tank caps are probably
inadequate to get much lower in freq.  Or you may just have a good
box of parts for some future amp project -- or two amp projects,
a 4CX250 VHF amp and a 3CX1000A7 HF amp.

Good luck--John   W0UN




At 07:35 PM 4/6/2004, you wrote:


>Hello Amp gurus,
>
>I picked up an amp at a hamfest last weekend.  It appears to be
>a homebrew job and I am wondering if you all might recognize the
>configuration and can point me to a magazine article or
>other info.
>
>I think I just have the RF deck.  The circuit employs a 4cx250B
>which appears to be driving a 3cx1000A7.  The filament supply and
>B+ to the driver are in this deck but the main HV is not here.
>My GDO says that the output circuit is resonant between 10
>and 20 Mhz.  (There was also a minor resonance around 80 Mhz.)
>I would guess that capacitors and other parts are from the 1960's.
>The front controls consist of a switch for filament and a switch
>for B+.  There are four fuses and four corresponding lights
>on the front panel.  They are labeled filaments, bias, B+ and
>fan.  Two large vacuum variable capacitors are in the output
>network, and their controls come to the front panel also.
>There aren't any meters on it.  Dymo tape on the front
>says:
>
>RF AMP
>SK-MP2-217 & SK-MP2-202
>
>And some old masking tape has the remains of a name, maybe
>Freyman?  and a note that says "max output 2.6 MW  kml 3-26-6.."
>
>If I can't get some better info on this thing I will probably
>part it out.
>
>thanks for any clues you might provide
>
>Chris
>kc0atc
>
>--
>Chris Howard                                     YipYap.Com
>chris at yipyap.com                                 Estes Park, Colorado  USA
>current Estes Park weather --  http://www.yipyap.com/wscurrent.html
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