Current Question

[WA4JK]

This may be next to impossible to answer.
Is there a way to calculate the amount of current at a given AC primary voltage drawn versus the Plate Voltage and Current output? or Watts delivered.
I'm looking at a fixed Voltage of 120vac and fix Amps of 8 amps and trying to come up with the best Rf GG amp. to produce 200w carrier and thus 800w at 100% modulation.

[WA1GFZ]

watt meter

[WA4JK]

No other end. Ac current at 120vac drawn for watts output at 2700vdc. Or am I just cornfussing the isse and should assume 100% rated current at inital switch on.
Say 0-1200W
what would be the currect on the primary 120vac for 0-25-75-100% load.

Am I crazy for try to find a formula or curve for this.

[WD8BIL]

Considering the yur AC line voltage is gonna sag at an un-predictable rate it would be a guess no matter how you calculate it.

[WA4JK]

So best to assume max draws at switch thrown. Minus soft start... oh maybe not. Thanks

[W2PFY]

Get an amp probe and put it in line and run your experiments is my best suggestion. You'll need a watt meter in the output or an RF amp meter if you know what the impedance of the line will be.

Now if you get one of these meters, you can measure amps all the time. It comes with the current transformer.

http://www.go2marine.com/product.do?no=83298F

What your looking for is throughput. power in vs power out equals efficiency of just the final stage.   

[KA2QFX]

I think your question requires more info.  Like are you building an amp and plate supply and want to know the start-up current or average running current?  Will the supply be cap input, choke input, etc.  Regardless of those specifics I can tell you that 120v @ 8 amps sounds a little light for a tube amp capable of 800 watts. 

I have run several amps over the years that can run 200 watts of carrier comfortably and they all pulled 20 amps at least (@120 volts) when tuned up to CW rated output. That being about 800 to 1000 watts of output. 

Generally speaking, for a power transformer, watts in = watts out + some small losses.  If you ignore the losses and assume an ideal DC supply, under full load 120v @ 8 amps = 2700V@ 355mA = 960 watts peak input.

An amp running 60% efficient would develop 640 watts, and that's being generous.  You'll also need to consider filament power and other extraneous loads and losses.  I'd say for 8 amps you're in the 400~500 watt PEP amp range.

[WA4JK]

Yep and there in lies the problem. I'm in an RV with a 15A supply outlet and I need 3A for the transceiver and that leaves 12A for Amp and Sb-610(1A) and  audio which is (1A). So effectally I have only 8Amps to play with. So it looks like a Al-811 is the only option. That might give me 130-150W carrier. Maybe.