[AMRadio] Power Levels

[rbethman at comcast.net]

----- Original Message -----
From:  <k4kyv at hotmail.com>
>
> What kind of line voltage do you have there anyway?  What is the DC plate
> voltage and current to the final?  It is supposed to run 2000 volts on the
> plate at 250 mills, on AM.  On CW it runs 2500 wolts at somewhere around
300
> mills.  Are you sure someone hasn't changed the tap connections on the
> primary of the plate transformer to boost the power by running it on AM at
> the full CW plate voltage?  If so, have pity on the poor hard-to-replace
> 250TH and restore it to normal operation.
>

I am positive the taps have not been changed.  This was restored to all
original condition very lovingly and tenderly after storage in either a
basement or garage.

> If it is running properly at 500 watts input, the Eimac tube sheet says
the
> carrier output should be 335 watts.  That assumes zero losses in the rf
tank
> circuit and associated components.  In the real world, at 500 watts input,
> you are not going to get more than about 300 watts carrier output, and
even
> that is being optimistic.  Because of the turns ratio of the modulation
> transformer, running the common power supply for modulator and final, you
> have a VERY good unit if it makes 100% modualtion on positive peaks
without
> distortion.
>

My SM-220 with Panadaptor shows no flat topping whatsoever.  The limiter in
the BC-614E has not been touched, nor do I intend to.

> Run the final at 2000 v and adjust antenna loading until the final plate
> draws 250 mills.  Make sure the grid current is at 60 mills, and adjust
> modulation for as close to 100% modulation as possible without negative
> overmodulation or flat-topping on positive modulation peaks as observed by
> the envelope pattern of an oscilloscope, and let her rip!
>
> Are you sure that at the time those wattmeters were in line, your feedline
> was presenting the transmitter with a precise 50-ohm nonreactive load?  If
> otherwise, the wattmeter reading WILL be in error.  The best check is to
> tune into a 50-ohm dummy load made up of high wattage noninductive
precision
> resistors, such as "glowbars".
>
That is the part that is hard to tell.  I do NOT have globars to make up an
appropriate 50 Ohm non-inductive dummy load for that power level.  Nor am I
in the position of acquiring them for the time being, even if I could locate
them.

> Don K4KYV

The only dummy load I do have, is a Bird 100W one.  It certainly would not
be very useful.

Bob - N0DGN
Manassas, VA