Re: VTTC operation, questions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ray von Postel by way of Terry Fritz <twftesla-at-qwest-dot-net>" <vonpostel-at-prodigy-dot-net>

Shad:
I couldn't agree more with the  suggestions that you look in Sam's and The
Radio Amateur
Handbook . Both are excellent sources.  As I understand it you are looking
for circuitry for
what they would probably call a "CW transmitter.". (CW = continuous wave).
Don't expect to
find construction details for something operating at TC frequencies.  They
will talk about
frequencies from above 1.5 MHz. to around 144 MHz.  Also, the power input,
for Hams,  was
limited by law to 1 KW.

Since you are building around the 833-A it would be well to get a
specification sheet for
that tube.  It will give you the typical operating conditions for  the tube
being operated in
CW service as a Class C amplifier.  Just remember, you will need a driver
for the 833-A.
It would have to put out enough power to drive the grid of the 833-A.  The
driver stage might
be driven by an oscillator operating at the frequency of the TC.  It might
even be possible
to use your signal generator to drive a lower power stage and do away with
the oscillator
stage.  Pulse modulation , keying, of one of the low power stages is much
easier than doing
so at the 833-A grid.  One particular tube configuration that comes to mind
is typical of
some transmitters I have seen.    6V6 oscillator, 813 driver, 833-A final.

My guess is that the two biggest problems you will have is the power
supplies, yes, more than
one, and winding the coils for the tuned circuits between the tubes.  You
have an interesting
project and I wish you luck.

Ray

Tesla list wrote:

> Original poster: "sundog by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<sundog-at-timeship-dot-net>
>
>     Hi All!
>
>  Christmas is nearly upon us, with all the ritual last-minute shopping in
> overcrowded stores elbowing your way past the checkout lines in a useless
> attempt to find the shortest one.  Tip I learned last year, the shortest
> line is that way because everybody in it moved to a faster line ;)
>
> Now, the serious stuff!
>
>     I've been digging through vacuum tube information, and am seriously
> kicking around the idea of grid-modulating a VTTC.  Principle is identical
> to a SSTC, you feed bursts of RF to the primary.  The 833A is well-suited to
> this task, and works at full power up to 30mhz I believe, so it should work
> fine at the 400-someodd khz range.
>     The more I go through the schematics, the more sense they make (I'm no
> EE, and tube gear is still funky to me).  There are some problems for me to
> overcome, but with my tube-driven signal gen as a working example of a grid
> tuned circuit, I think I can do it.
>
>   Steps to this project :
>  - Build a high-powered DC supply.  I'm acquiring the MWO's for this.  I
> want about 3kv -at-1A available on a full-wave rectifier with a good-sized
> resevoir cap.
> -  Build the small grid-tuned oscillator.  The signal gen is going to be a
> world of help here.
>
>  I have the rest of the parts that I'll need (the push-pull VTTC primary,
> etc.)  I don't forsee this project being a fast or easy one, but it should
> be fun and educational.  Plus the 833's are "just a little more tolerant" of
> mistakes than a MOFSET ;)  Most non-disastrous flaws show up as decreased
> output and increased tube dissapation.  In all honesty, the driving system
> for the 833's will be the most challenging.  Eventually I want to modulate
> the preamp tubes with solid state gear for adjustable duty cycle and better
> modulation control.
>
> A note to all MOT scroungers, the few days after christmas are some of the
> *BEST* days to find MWO's sitting on the curb.  A kind work and smile to the
> old owner is usually all that's needed to get permission to retrieve it from
> it's fate.  Curb-raiding is highly frowned upon where I live (guess how I
> know?)
>
>          Comments, questions, and snide remarks welcome!
>                                                 Shad