How much power output do you want?
A single 833A has a plate dissipation of 400 watts. This means it
will run amateur intermittent service at 1600 watts DC input to the final
class C and deliver with at least 75% efficiency 1200 watts carrier output.
It will run 1KW input all day long at more than 750 watts output modulated
to much more than 3000 watts PEP.
A single 4-125 running intermittent amateur service will do 500
watts input at 75% efficiency yielding a carrier of 375 watts. It will
operate all day (with a little cooling fan) at 400 watts input and 300 watts
output with more than the legal limit of PEP or with a sine wave modulating
it at 12 watts PEP.
A single or pair 4-125 modulated by a pair of 4-125s would be my
choice for running legal, cool, and using smaller components for a smaller
foot print.
If size, weight, and time are of no concern, a single or pair of
833s modulated by a pair would be my choice.
If you use the 833s, use a push pull link coupled output circuit
with cross neutralization. Even if only one tube is used, build it as if it
were push pull, just leave out the other tube and neutralizing capacitor.
A single 4-65 makes a very nice RF driver for the 833s. I recommend
running it class C with initial tune up to a dummy load then reduce the
Ep/Es supply for drive level to the 833s. I think a single 833A class C
only needs about 20 watts to drive it. If you consumed about 20 watts in a
dummy load paralleled and another 20 in drive (a total of about 40 watts)
and had very tight coupling to the grid then the neutralization of the 833A
would be very easy even with the single tube.
John,
WA5BXO
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
On Behalf Of Jim Isbell
Sent: Thursday, December 11, 2003 3:14 PM
To: amradio@mailman.qth.net
Subject: Re: [AMRadio] AM from what I have in the junk box
Great idea. I have enough tubes to do two of anything...including the 833s
Todd Bigelow - PS wrote:
> Jim Isbell wrote:
>
>> Anyone have any nice schematics to construct a AM transmitter from
>> some 4-125As or 4-65As that I have available?? Also have a new 833a
>> that could be used for a modulator.
>
>
> How about pounding the 833 with a pair of 4-125s as modulators? You
> might be able to adapt some of the circuitry from a T-368 since it
> uses 4-125s into a 4-400, or at least get a bit more of a start on it.
>
> de Todd/'Boomer' KA1KAQ
>
>
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