[AMRadio] gas tube protection of front end

Edward Swynar gswynar at durham.net
Mon Mar 2 13:27:10 EST 2009

Hi John,

That very technique, i.e. the installation of a gas-fired bulb from the
antenna terminal to ground, was used in the RCA AR-88 receiver of 1944...


Apparently many of these rigs had occasion  to operate physically close to
QRO transmitting installations --- I guess the bulb was the WW2 equivalent
of back-to-back diodes in the protection of receiver front ends...

~73~ Eddy VE3CUI - VE3XZ


----- Original Message -----
From: "John Lyles" <jtml at losalamos.com>
To: <amradio at mailman.qth.net>
Sent: Monday, March 02, 2009 1:18 PM
Subject: [AMRadio] gas tube protection of front end

> Ne2 or Ne51 or whatever you have in it, are good for protecting hollow
state front ends. As they ionize between 50 and 90 volts, they will conduct
static buildup before it builds enough to open a coil in the front end.
Although i have never heard of that happening either. Commercial receivers
sometimes use more expensive devices like Claire makes, with a narrow
specification for breakdown voltage. The capacitance of a neon bulb, before
it ionizes, is low. For solid state RX, however, neons might not have low
enough breakdown to protect fets, varactors, etc. You cannot simply put an
MOV or transorb across a HF circuit as it will have a lot of capacitance.
Sometimes back to back diodes are applied. Spark gaps and gas tubes still
> John
> > Message: 1
> > Date: Mon, 2 Mar 2009 00:57:58 +0000 (UTC)
> > From: w0ng at comcast.net
> > Subject: [AMRadio] Receiver Antenna Input Question
> > To: boatanchors at mailman.qth.net, amradio at mailman.qth.net,
> > national at mailman.qth.net
> > Message-ID:
> >
<1524953191.2309561235955478082.JavaMail.root at sz0147a.emeryville.ca.mail.com
> >
> > Content-Type: text/plain; charset=utf-8
> >
> > Would appreciate some advice here. I have a National NC-303 receiver
that I'm restoring. I had a 75A-2 once that had a neon lamp (NE-2 ???)
across the antenna input connection to supposedly act as a surge supressor
for lightning, strong static charges?and strong rf energy from nearby
transmitters. Is this a good idea? Does this really work? Is there a better
device than a neon bulb? Appreciate any opinions, etc. 73, Bill, w0ng
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