> From: Gary Myers <gmyers@cetlink.net>
> I tried three different meters including a Bird! I did use the internal
> meters for input power.
OK, then the range of the estimate you made is probably as I
posted. So you are in line with what Carl and I measure.
> The only thing that bothers me unless the mod
> changed things, is the engineer from the factory agreed with the numbers
> I gave him!
I wonder who that was, and why he didn't make himself clear? Maybe he
didn't know the answer?
> This was after several calls and lots of tries tuning. I
> have asked several times since then (over 10 years ago) if they had
> changed the design to improve the efficiency but have never gotten a
> decent answer.
Maybe that was me ten years ago, in a stupid moment. ;-) I
worked there back then.
In about 1985 a mod was added to neutralize the PA, that moved max
output into the dip and improved things somewhat.
In about 1989 or so, after I left, I was working on a new
3-500Z amp design for Heathkit. The amp had bad efficiency problems
(30% or so) on ten meters. It turned out the input system was
presenting a high impedance to the tube on the third harmonic of ten
meters, and that was murdering the efficiency.
I put Ameritron "on to" this problems, and checked the 3-500 and
3CX1200 amp for them. Both had modest cathode impedance on ten
meters, so lowering it did help efficiency about 5 to 7 percent. My
data indicates efficiency was around 51 % on ten meters before and
57% after the input mods.
Another ~5% improvement in output power can be had by installing a
vacuum plate cap and re-working the tank, and with a mono-band copper
tubing tank I got almost 10% improvement in output.
IMO, unless you work RTTY any tank change isn't worth the money or
time... but the input system sure is because it reduces heat in the
tube.
73, Tom W8JI
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