Spark Gap chart for ball and needle gaps in transmitters.

[Opcom]

This is from an older FAA manual.

[w4bfs]

thanks Pat .... this is hard to find info  

n.b.  this gap info is for dc and audio freq ac .... if rf is involved the spacing required opens out fast 

[W2PFY]

I wonder how they tested the spark gaps for the appropriate gap?

Ok Sam, now increase the gap by one thousandth. Done. Did it spark? Yes! Now set the gap to...........

I'm such a nerd that I printed it out...

[Opcom]

The chart is from a book for the 1937 Westinghouse TSC transmitter which was used to make navigation beams for aircraft. I don't know where the book was on the internet. Being from '37 I trust it was done the "old man way".

The only TSC transmitter I have ever seen in person is at the Oregon Air and Space Museum. It's a monster. The transmitter has two simultaneous functions: radio range and telephone. It coversd 200-400KC and makes 275W on the sideband channel and 400W on the carrier channel. Has a bunch of 805s inside. It's built like a battleship. It was available, with the side panels off, to visually examine in minute detail and I spent about 2 hours just taking it in, looking at it from every side.

[W2PFY]

I think I may have seen the same model or one close to it. In this case it was a transmitter on eBay being sold by a guy in Canada. He had the side covers off and like yours, it had a bunch on 805 triodes in it. I think it may have had about 12ea 805's in it where they were either in push pull parallel or were hot spares. I think this unit was built by the Canadian Marconi works. I know that 12 805 tubes seems like a large number 805's for one transmitter but that is why it stands out in my memory. Another possibility is that the 805's may have been arranged in such as way whereas one tube may have handled a certain segment of a given band and had a common class B modulator for the whole rig?

Well I started to research the Canadian Marconi Company to see if I could fine the transmitter but so far, no luck but I did find a bunch of other interesting stuff with big old ships transmitter etc that will keep me busy for a few hours tomorrow!

Maybe I'll find that transmitter and if I do, I'll post it here.