[Milsurplus] What's With 2,000 Volt, 50-Watt Xmtrs??

[mac]

Fifty watts out with 2KV on the plate is the (suppressor) grid  
modulated specification for the 803.  The tube is good for 200 watts  
out on CW with the same plate supply.  Designers choice, maybe, in the  
case of the AVT-12 to save the weight of a modulation transformer and  
extra circuitry of a plate modulated rig designed around lower  
voltages. Same route taken in the TBW for ex.  Pair of 803s in the TBL  
good for 100W phone and 400W+ on CW as Howard mentioned.  Same deal in  
the TCK with a pair of (control) grid modulated 813s in the PA..

Dennis D. W7QHO
Glendale, CA

*****

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On Nov 17, 2010, at 9:11 AM, David Stinson wrote:

> I've been looking at some transmitter diagrams
> that use tubes like the RCA 803 and its kin.
> Take the RCA AVT-12:  This is a simple, late '30s
> xtal-osc-power-amp transmitter intended for
> small aircraft which delivers about 50 watts out on phone.
> The high B+ for this thing, supplied by an external
> dynamotor over a long run of cable, is like 1700 volts.
> Why?  RCA designed similar rigs about the same time
> that delivered that level of power with 500-600 volts.
> Get a GP and start thinking about 2000+ volts to
> deliver less than 100 watts.  That kind of voltage
> in the dirty, greasy, gas-vapor-y environment
> of a 1930s-40s aircraft seems...ummm....
> not well thought-out (read "stupid and suicidal").
> Other period equipment demonstrates doing so was unnecessary.
>
> Whenever someone otherwise brilliant pens a design
> that makes as little sense as creating the 803 to deliver
> modest power with Tesla-esk voltages, I smell money
> at the root of it.  Did RCA tube designers build the 803 and
> other tubes like it to get around someone's patents?
> That would certainly fit-in with all the radio patent fights
> in the 30s. How many different ways can you make a tube,
> anyhow?  They'd have to do something different to avoid
> royalties to someone, like design a 50-watt circuit
> with 2200 volts of B+.
>
> OK, People-Smarter-Than-Me:  What do you think was the
> motivation to design low-power-out circuits with
> dangerously high B+ voltages?
>
> 73 Dave S.
>
>
>
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