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

[John Hutchins]

All -
I think Dennis  go to correct.  Screen grid modulation smaller and 
lighter transformer at less voltage and current.
Also for aircraft, correct me if I am wrong, screen grid modulation 
would have less tendency to Arc at high altitude?
-Hutch

On 11/17/2010 12:00 PM, mac wrote:
> 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
>
> *****
>
> The Tea Party - thousands of hard-working middle-class FOX viewers
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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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