What program did you use to calculate values?
Carl
KM1H
----- Original Message -----
From: "Chris Miller" <c_miller_1@hotmail.com>
To: <amps@contesting.com>
Sent: Friday, December 28, 2012 10:49 PM
Subject: [Amps] looking for assistance with MLA-2500 tank circuit rework
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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