813 tube coil (comments on PSU)

From:  Jim Lux [SMTP:jimlux-at-earthlink-dot-net]
Sent:  Thursday, June 04, 1998 11:37 AM
To:  Tesla List
Subject:  Re: 813 tube coil (comments on PSU)

Tesla List 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 think I've got the main PSU figured,
> 1) Rig it so that it cannot be switched on unless the heaters are on.
And so there is a time delay to make sure the filament is HOT. The
classic approach is a thermal time delay relay, it cools at the same
speed as your tube, so if there is a momentary power interruption, you
don't have to wait the full heat up time.  Of course, solid state time
delays are cheaper and readily available.

> 2) 2200V AC microwave transformer fed off my 4A variac,
> no need to rectify - the tubes will do that but I can experiment with DC
> later.
> 1A meter to monitor HV current.

Make sure the meter is in the low voltage side of the power supply, or
insulate the case from ground (and you).  Put a protective resistor (or
zener) across the meter, so that if it fails open, the voltage doesn't
rise to the full supply.  This is a bit tricky with a transformer where
one end of the secondary is grounded, but you could probably safely run
the core of the transformer off ground, tied through a reasonable
resistor (say, several hundred ohms).