[AMRadio] Power Levels

[Brett Gazdzinski]

I always figure on roughly 70% efficiency, so....

2500 volts, 250ma, 625 w in, 437 w out, 187 w plate dissipation.
2500 volts, 280ma, 700 w in, 490 w out, 210 w plate dissipation.
2500 volts, 300ma, 750 w in, 525 w out, 225 w plate dissipation.
2500 volts, 320ma, 800 w in, 560 w out, 240 w plate dissipation.

If the 250 th is anything like the 100th tube, it likes higher
voltages, and is supposed to glow the plate yellow under 
normal use.

Steve, N2DXM once built a push pull 100th rig, and said
it would only run 250 or so watts out.
I asked him how he was running the thing, and found out
he adjusted things till the plates started showing color.
Well, at 2000 volts, my 100th modulator shows
an red/orange color at resting current!

Same with the 4-125 tubes, if you run them to where they
just show some color, they are way under loaded....

 

Its fine to run it up as high as you like in the plate dissipation
up to 250 watts, as long as it will supply the additional
power for the audio peaks.
That is not the best way to get the tube to last a long time,
but ok if you have spares....

If you were to go with 2000 volts, the current would be much higher...

2000 volts, 300ma, 600 w in, 420 w out, 180 w plate dissipation.
2000 volts, 350ma, 700 w in, 490 w out, 210 w plate dissipation.
2000 volts, 380ma, 760 w in, 532 w out, 228 w plate dissipation.
2000 volts, 390ma, 780 w in, 546 w out, 234 w plate dissipation. 

I think efficiency will take a hit at 2000 volts though.
I know its not supposed to, but on all the rigs I have checked,
the efficiency was higher at higher voltages, or at least,
the power output was higher at the same plate color with
higher plate voltage.
Some tubes get better modulation at lower plate dissipations though.
No problem at all running a pair of 813 tubes at 2200 volts
and 400 ma, I get lots of peak power, while the 811/812
deck likes to be run at lower power inputs, mostly lower 
currents, otherwise the tubes seem to run out of emission
on peaks.
If I use 1700 volts, as I load the thing up, the peak
power stays the same after some (modest)point, and 
the carrier power goes up.
So say I get 1200w pep max, I can run the thing at 280 watts out,
300 watts out, or 350 watts out, but still only get 1200w pep.
 

Brett
N2DTS
 
> 
> From another member of the reflector who doesn't want to get 
> involved in any 
> "flame war":
> 
> "...But I DO know one thing for sure! If I ran my TH at 390ma 
> for any length
> of time, it'd
> be TOAST! Hell, it gets cherry red at 240mills!
> It's been a long time since I read the BC610 manual, but I sure don't
> remember anything like that 390ma stuff Jim is talking about! In fact,
> in the back of my mind, I think the manual said somthing like 240mills
> for AM."
>