813 tube coil

From:  Mike Harrison [SMTP:wwl-at-netcomuk.co.uk]
Sent:  Thursday, June 04, 1998 9:10 AM
To:  Tesla List
Subject:  Re: 813 tube coil

On Wed, 3 Jun 1998 20:15:05 -0500, you wrote:

>From:  Alan Sharp [SMTP:AlanSharp-at-compuserve-dot-com]
>Sent:  Tuesday, June 02, 1998 11:08 AM
>To:  INTERNET:tesla-at-pupman-dot-com
>Subject:  813 tube coil
>Thanks to those who responded to my questions
>about the 813 valve.
>I've got some data and ideas now. I think I've got
>the filament sorted out. The filament doubles as the cathode,
>so I need a 5-0-5V supply - to keep everything symetrical.
>I also need to adjust this to 5A per tube, I'll also use an inrush current
>limiter -
>to avoid a switch on surge shortening the life of the filaments.
>Naturally no one supplies 5-0-5V transformers at 10A - so
>I'll probably use a 100VA transformer kit and wind my own secondary -
>(then I can put on / take of turns to get to the exact current/voltage).
.. Or you could use a toroidal transformer and overwind the required
secondary - I've often seen big-ish toroids  going very cheap at radio
Big 5V switchmode supplies are also ten-a-penny, but you'd have to be
careful to avoid zapping them!
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