[AMRadio] Re: max output off dip

[Gary Schafer]

RABRUNER at aol.com wrote:

> I have never seen a plate modulated AM transmitter that didn't put out more
> RF off dip.  In fact, this phenomenon was used in many AM broadcast
> transmitters.  The RCA BTA-1R series of transmitters (2 4-400s modulating 2
> 4-400s) had fixed output coupling.  The instructions were to adjust the
> output loading by moving taps on the coils until you achieved about 80 per
> cent of the required power, and then run the plate tuning off dip until the
> desired power was obtained.  Even transmitters which had adjustable output
> coupling would offer the same instructions.  Transmitters that I engineered
> that worked this way included the Gates BC-5P, BC-1E, BC-1G, the Collins
> 30-V3, and RCAs referenced above.  In fact, on the RCA, if you tired to load
> it up 'on dip' you would not make power.  You get more efficiency out of a
> class C plate modulated amplifier if you tune it to the 'High" side of dip,
> often referred to as the capacitive side of dip.  You can improve the
> efficiency of your finals better than 10 percent this way.  This is because,
> while the input to the stage increases as you run the tuning 'Hi C', the RF
> output is going up faster.  Even linear amplifiers work this way. Anyone who
> has experience with a Heathkit SB-220 for instance will not that the
> instructions are to dip the play and then adjust the final for maximum output
> using both the tuning and loading.
>
> Bob Bruner
> WB4TAJ/9
>

I have a plate modulated AM transmitter that has max output at minimum plate
current. A DX100. If the neutralization is off then it indeed does perform as you
describe but max output can be on either side of plate dip depending on which way
the neutralization is off.
I will guess that all of the transmitters that you mention above did not have
neutralization?

The Sb220 may provide more output off dip but that is because it is not
neutralized and may have some regeneration. Yes I have seen many amps that do not
deliver max output at dip but I have also seen some that have max output at
exactly the dip in plate current. No significant unwanted feedback.

73
Gary  K4FMX