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valve diode tubes ? (fwd)
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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