[Amps] MLA-2500

EP Swynar gswynar at durham.net
Fri Jan 25 14:12:13 EST 2008


Hi Again Ken,

"...Could the fact that I'm using a tuner and not a resonant antenna for
each band cause this?"

***********************************

I think not, Ken --- the tuner transforms whatever impedance the wire /
antenna might "normally" present in & of itself, into one that the amplifier
"wants" to see in order to work properly, i.e. 50-ohms, or so.

Here's a thought: take a look at one of the HANDBOOK chapters on RF
amplifier design, & look-up the calculated values for the plate tuning
capacitor, loading capacitor, and tank inductance for the specific output
impedance of your tubes...then, when you have the amplifier tuned & loaded
"properly", compare the amount of "meshed 'C'" you have in the loading cap,
to the text book specs...

That'll at least give you an indication of how much the loading cap SHOULD
be meshed.

I had a similar issue here awhile back with my homebrewed 2x813 kilowatt,
i.e. the fixed padding capacitors I had were over-heating on me, changing
values...but that was only on 160-meters. In your instance, like mine, I'm
sure the design doesn't have any need of incorporating extra "C" on
frequencies as high as 21-, or 28-MHz! If anything --- assuming padders are
the culprit --- the amp should function "normally" on the higher bands.

Then again, maybe that linear of yours uses something like a 4-, or
5-section air variable in the loading stage, and the bandswitch
progressively adds, or deletes, sections dependent upon frequency...as a
result, if only ONE section is used on 10-meters, it could very well be that
the doggone thing would be almost fully meshed, to achieve the right value!

In other words, it really IS normal! Hi Hi.

I wish I had a schematic of that rascal...

Say, Ken, is there any kind of a "logging scale" in the manual that might
"ballpark" the settings of the unit on a band-by-band basis...? And if so,
how close are your settings to those of the manual...?

~73~ Eddy VE3XCUI - VE3XZ



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