Hi Chris, 2700 ohms plate load R seems a bit high. What plate voltage and
current was that figure based on?
73,
Gerald K5GW
In a message dated 12/30/2012 2:49:54 P.M. Central Standard Time,
c_miller_1@hotmail.com writes:
Hi to all,
I have taken on a project that has been bugging me for a bit. I have a
MLA2500 that I picked up that has been retrofitted with a pair of 3cx800
intending to have a transportable amp. From what I have read the tubes
are
supposed to be a close match for the original tubes, as far as tube specs
go. However, I have found that the amp on 160 through 40 has to have the
load control set to 1 to get close to load on power. 20 through 10
appeared
to work o.k.
I decided to sweep the tank through the antenna, with a 2.7k ohm resistor
in
place on the anode to simulate tube load and found that resonances
appeared
off on lower bands. Figuring I had a good handle on the process, I
prototyped up a new tank coil to make mistakes on. I then playing with
tap
points and turns until I achieved what looked like a good set of patterns
for each band, for the range of tuning.
When I attempted to test my results, on dummy load conditions, all bands
are
now showing insufficient capacitance for load on all bands with a little
bit
of range at near max capacity on 10 near the upper end of the band.
Since that seemed to be an epic failure, I must be missing steps in the
process. Is there something I should be watching for or doing so that
what
I see as tank resonance actually lands where it should on real world
testing? Am I now at the point where I have to do some trial additions of
capacitance to the load control? Is this amp worth the effort to make it
work properly (realizing it is a bit of a sardine can in there)? Has
anyone
else done the retrofit on these amps to the 3cx800 tubes, like this amp
has,
and did the amp still resonate as the original tubes did?
Thanks for any help
Chris VE3CEA
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