Try checking out the Svetlana Web site under tech notes and you will find a
conversion to a 4CX800 single described there. The 4CX800 is much cheaper than
the 3CX800 and is the socket is only $22. Even if you were to add the
G3SEK-DownEastMicrowave screen/grid protection boards it is still cheaper than a
pair of 3CX800 and a single 4CX800 will do about the same output as the pair of
8875's you now have, approx. 1200 to 1300 PEP and an easy KW out for RTTY or
SSTV. The power supply of the MLA-2500 will keep up with the demand if you keep
the cooling working on the transformer as well. Not CCS service mind you but
the typical 10 Min on/ 10 Min off stuff even full tilt it will work.
Don't forget to use some of the Rich Measures mods like a glitch resistor in
the HV supply and the full QSK mod with the RJ1A and associated circuit stuff is
fairly simple to incorporate. Check out the measures home page for a good read
before diving into the amp.
Also, check out the G3SEK home pages as well. The "In Practice" articles
also quite valuable. Don't overlook the archives of this reflector as well.
Lots of good stuff available and you won't have to go thru the usual
"reinventing of the wheel".
Lastly, draw a complete schematic of what you want to accomplish and make a
plan of attack on the rebuild. It will save you a lot of "Oh-shits" later when
something doesn't quite work as planed or you get a bit tired while working on
the project and you get something smoking.
Don't work on it if you are dead on your feet. It will cost you $ and time
in the long run from the careless mistakes, and lets not forget the alternative
to getting into the HV by mistake. Unless you are anxious to become "room
temperature" keep one hand in your pocket while working on a "Live" amp and
"Assume" anything. Unplugging the amp and carefully discharging the power
thru a series of 1 Watt 5 to 10K resistors on a "shorting" stick can save your
life. You get NO second chances with HV.
Respect for the voltages present, a systematic plan of safely discharging
power supply, removing the fuses and unplugging the amp from the wall, matched
with a planed attack on how to accomplish the modifications successfully will
up a project you can be proud to show off to your friends and you can "live"
I have similar designs in mind for an ultimate conversion of a GLA-1000 in
the works myself.
If you still have questions after doing your "plan", you can still inquire
the group as there is a lot of experience and a wealth on knowledge within the
folks here on the reflector.
Mike Baker KØQZ
> Hi Rich here,
> I am new to the group and I interested in converting a Dentron MLA-2500
> from 8875's to a pair of 3cx800a7's. Does anyone have the plans to make such
> a swap?
> I have some documentation to convert the amp to other tubes but I am
> interested in the above modification. If anyone has done this, I would
> appreciate some pointers,pics, pitfalls etc.... Tnx in advance!! Richy
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