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valve diode tubes ? (fwd)
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From: D.C. Cox [SMTP:DR.RESONANCE-at-next-wave-dot-net]
Sent: Monday, August 17, 1998 12:32 PM
To: Tesla List
Subject: Re: valve diode tubes ? (fwd)
to: Chris
Resonance Research carries Varo VG-20 in stock. Rating is 20 kV at 40 ma
continuous current.
DR.RESONANCE-at-next-wave-dot-net
> From: Ed Phillips [SMTP:evp-at-pacbell-dot-net]
> Sent: Sunday, August 16, 1998 3:40 PM
> To: Tesla List
> Subject: Re: valve diode tubes ? (fwd)
>
> "
> On Wed, 5 Aug 1998 17:10:03 +0100 Chris Swinson
> <chris.swinson-at-zetnet.co.uk> wrote;
>
> > I'm after a diode or valve that will handle 240 watts min, thats
> > at 8Kv -at-30 ma. This must be the minimum spec.
> >
> > Does anyone know of a supplier for them or how much they cost or
> > anything really ?
>
> Chris, almost any High voltage rectifier from a T.V. will exceed you
> requirements
> (tube or solid state)! Some numbers for you are; 1AD2, 1B3GT, 1G3GT,
> 1K3GT, 1N2A
> all have the following specs - 26KV -at-50 ma. (pulsed) 33KV -at-33 ma R.F.
> Look in any old RCA Recieving tube manual and you will see dozens of
> tubes that exceed your specs and almost all of those tubes can be had
> for
> less than a dollar at a surplus electronics store."
>
> NO WAY!!!!! Any of these tubes will probably melt down if you attempt
> to pass 30 ma through them. A look at the tube handbook shows that most
> of these are rated at a specified voltage drop at 7 mils.
>
> 1AD2 225 V -at- 7 ma
>
> 1B3GT 100 V -at- 7 ma
>
> 1K3 225 V -at- 7 ma
>
> Similar ratings apply to all of the TV HV rectifiers. The typical
> average current maximum is about 1 ma. If you tried to draw 30 ma out
> of one continuously the plate voltage drop and hence the plate
> dissipation would go way up, the plate would get red hot, the tube would
> become gassy, and end of the line. For the 1B3, for example, the
> voltage drop at 33 ma would be of the order of 500 volts and the plate
> dissipation would be about 17 watts!!!!!!!
>
> Another problem is that these tubes use oxide-coated cathodes, which
> would probably fail very quickly at such current levels, even if they
> had enough emission initially. The filament power for these tubes is
> typically around 0.25 watts, way, way below that for a typical power
> rectifier.
>
> Bottom line is don't try them, unless you are prepared for unhappiness.
>
> Ed
>