[Johnson] Valiant Low Power and Plate Impedence Matching

[radioman]

Ok.. to run low power CW... just reduce the loading and re-resonate the
plate to achieve the plate input (or output) desired.

This is how you could run Valiant..or any other high power transmitter
legally, when novices were limited to 75 watts input.

+ACoAKg-AM PHONE IS ANOTHER STORY ALTOGETHER +ACoAKg-

Mod Z +AD0- Ep/Ip

That means the load impedance -Z -the modulator tubes and transformer
see depends on the  final Plate voltage Devided by the Plate current.

When you create a mismatch between Modulator and final by increasing or
decreasing the final Plate Current setting... you will cause:

1. Audio Distortion from impedeance mismatch ( the mod transformer Z is
fixed).... while the same Ep/Ip rule applies to the modulator tubes to
establish thier impedance.. as it did to the finals.. the transformer is
supposed to match the two... hard to do with moving targets +ACE-

2. HV Flashovers ( second audible warning) ..  power not delivered to
the finals has to go someplace..and it jumps the gap across the
modulation transformer secondary to protect it from burnout.

3. Burn Up your Modulation Transformer.. if you ignore 1 and 2 ... then
you get the built in smoke warning... and a chance to go on a treasure
hunt for a new modulation transformer for a 45 year old transmitter.

Like the attorneys from General Motors said +ACI- the smoke comming from the
carpet of your Chevrolet, is your warning that the catalytic converter
is overheating+ACI-

Moral of the story is this... the only safe ways to reduce the power of
your AM transmitter are :

1. Turn down the Mic Gain... which reduces PEP but not carrier level.

OR

2.  adjust the screen voltage  or plate voltage of BOTH the Finals and
Modulators so thier plate impedences stay in the same proportion.. and
retain the same value.. which will allow your modulation transformer to
match them.

Brodcast transmitters that have to go from say 5 KW to 500 watts, do so
by changing Plate Votage to both modulator and  PA.


Larry W6WUH