[Boatanchors] 813 grid to filament short

[rbethman]

Hello Sheldon!

Long time since I've seen a post from you!

I don't have such a late edition of Terman's.  Mine is the 1943 edition.

In any event, there has been a whole lot of Bovine Scatology tossed around!

ERP has been tossed into this mess.  Obviously it is another red herring!

The 375W @ 100% modulation will indeed get you 1500W PEP *if* the 100% 
modulation is symmetrical.

The human voice is anything but symmetrical.  This is where the majority 
of folks start getting off the real path of meaningful numbers.

I only wish that there was a REAL way to measure PEP of any voice 
modulated signal.

I do have a peak reading Bird, and the necessary slugs that are 
compatible with it.

Then the real rub!  Whom owns an antenna system that is a pure 50 Ohm 
resistive load?

I haven't found one of those either!  No 50 Ohm resistive load, no 
realistic numbers!

This discussion started as more of a classroom exercise in lieu of any 
realistic look at the tried and true real world.

The only place that can measure this PEP with any degree of accuracy is 
up the road a bit from me, and that would be NIST, (National Institute 
of Standards and Technology), and I don't think we will see them get 
into this.

My Bird has a calibration sticker on it, but it is long out of its due date.

The entirety gets back to 813s and mounting them horizontally. Bad 
move!  W3BYM uses 4 813s to modulate 4 813s.  Should one dig up the old 
ER issue, you'll find that he mounted them vertically! The only 
intelligent way to do so.

Simply because Heathkit used 572Bs and mounted them horizontally does 
not indicate good engineering practice!  Yaesu also tried that back with 
the FL-2100B.  Another wonder that was a problem child.

It is another exercise in futility to attempt to deal with Amateur 
Radio.  What sort of feed line is used?  What band?  If it is coaxial 
fed, then is it the proper length for THAT band?

The variables are vast, and there is less sense in the discussion.

Regards, Bob - N0DGN





On 10/1/2015 3:05 PM, Sheldon Daitch wrote:
>
> Bob,
>
> Terman is up to the challenge.
>
> My 1955 Terman's Electronic and Radio Engineering, Fourth Edition, page 530, chapter 15, section 2, in the miscellaneous aspects of plate-modulated Class C Amplifiers, and tubes typically used:
>
> "Plate-modulated Class C amplifiers normally employ the same triode, beam, and pentode tubes that are used for ordinary Class C amplifiers.  However, the rated d-c plate voltage and carrier power of a tube used for plate modulation are less than the corresponding ratings of the same tube when used as an unmodulated Class C amplifier.  This is because at the peak of a completely modulated wave, the equivalent plate-supply voltage applied to the tube is twice the d-c value, and the power output at modulation peaks is four times the carrier power.  However, the tube operates at these peak values for only a small fraction of the time, and the average power power output generated under fully modulated conditions is 1.5 times the carrier power."
>
> Also see:
>
> http://www.w8ji.com/amplitude_modulation.htm
>
> and
>
> http://www.pa2old.nl/files/am_fundamentals.pdf
>
>
> 73
> Sheldon