Re: Tuning Primary

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Ed Phillips <evp@xxxxxxxxxxx>

The size problem was my first thought, too. But how about this one:
The old style variable cap from tube/valve radios, some have 2x500pF.
Not much, but with maybe ten of these ganged together, this could give
a pretty nice tuning range combined with a MMC.
Of course, these caps usually don't stand more than a few hundred volts,
maybe 1KV,,, dont really know, but under oil they should be able to run
a few KV. Pretty messy solutions, but might work for "online tuning".
Tuning by variable capacity would after all be more desirable than using
an external tuning coil."

   I have such a tuning capacitor arrangement : four 4-section (500 
uufd/section) geared together and immersed in a large plastic box 
filled with transformer oil.  Total capacitance is around 0.008 
ufd.  These are large capacitors with larger-than-usual spacing for 
receiving capacitors but in spite of that and the oil the breakdown 
voltage is low enough that I didn't have any luck tuning a small TC 
run from a 2800 volt, 20 ma NST.  I didn't build the thing (someone 
gave it to me) but I don't recommend that anyone go to the trouble.

Ed