Hi Bob,
I have done the conversion using 2 x 3CPX800A7. With the original HV power
supply I get fill legal limit output on 160-20m and 1300 W on 15 and 10m
(measured on dummy load with Bird 43). In continuous operation the
transformer needs some cooling - I mounted 2 fans on the top cover.
You need to make an air plenum to allow airflow through the tube cooling
fins. Expoxy PC board material is ok for that. I use a radial blower instead
of the original axial fan. Besides that I use a separate filament
transformer mounted to the rear panel and added a 3 min. warmup-timer.
There are some articles around concerning conversion of the MLA2500 to
3CX800. I recommend reading the Svetlana TechnoteNo44. Other articles as the
Svetlana TechnoteNo14 and by AB6YL in QST May 1996 refer to the conversion
to other (single) tubes like the 4CX800A. I think converting to 2 x
3C(P)X800 is the easiest modification though.
You can download the Svetlana Technotes, additional info and some pics of my
amplifier from http://dk9ip.ba-karlsruhe.de/pdf/mla2500
73 de Win DK9IP/KH7CD
> --- Original message ---
> Von: "k6zz@mail.ccis.com" <k6zz@mail.ccis.com>
> An: amps@contesting.com
> Betreff: [Amps] MLA-2500 Power Supply Capacity
> Datum: Thu, 19 Jan 2006 02:33:00 GMT
>
> Hi Folks,
>
> I could use some advice on the MLA-2500 power supply. I'm
> planning to put a pair of 3CX800A7's in a tubeless but
> otherwise very good condition MLA-2500. It seems like a
> straightforward modification, but I am somewhat concerned
> about comments I have seen regarding the ability of the
> power supply to handle these tubes. What is it about these
> particular tubes that would put an extra strain on the power
> supply? If they aren't driven any harder than the original
> 8875's or a pair of 8874's, what difference would it make?
> I could use different tubes but I happen to have a good pair
> of 3CX800A7's so I'm inclined to move forward if the power
> supply can handle it.
>
> I have no desire to push the modified amplifier to power
> levels beyond its capacity, but I would like to comfortably
> run the amp at the legal limit if the power supply and tank
> circuit can handle it.
>
> Have you done this particular modification before? Is the
> power supply up to the task? If not, what can be done to
> improve its shortcomings?
>
> 73, Bob K6ZZ
>
>
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