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813 tube coil (comments on PSU)
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From: Robert W. Stephens [SMTP:rwstephens-at-headwaters-dot-com]
Sent: Thursday, June 04, 1998 10:59 PM
To: Tesla List
Subject: Re: 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).
A much safer place to install the 0-1 Amp ammeter is in the center
tap return to ground from the filament transformer winding to the
oscillator power tube. The positive meter terminal goes to the
transformer center tap. The meter should be bypassed with a 0.1 uF
cap rated at 600-1000 volts.
The meter can be installed normally in the metal grounded chassis
without special insulation techniques, and if it goes opem the coil
just stops operating. The disadvantage to this is that the meter
will read combined grid and plate current of the tube, probably not a
big deal in this application. It will certainly give a good
indication of system tuning, loading and how hard the tube is being
thrashed.
Robert W. Stephens
Director
Lindsay Scientific Co.
RR1 Shelburne, ON Canada L0N-1S5
Tel: 1-519-925-1771 Fax:
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