[Hallicrafters] Screen Protection - SR-2000

[Bill Gerhold]

I made a simple circuit to avoid damage to the screen of power tubes but not
in the SR-2000 however the method still applies.

I broke the screen supply lead of a homebrew 4CX250B power amplifier, and
inserted a .5 or 1 ohm resistor in series with the screen lead (your value
would have to be found mathematically for your tube).

Across this resistor, I placed a IR diode and fixed it in place
mechanically.  Directly across from this diode and looking directly at it
was an IR detector (about 1/4" away).  When too much current flows to the
screen grid, the voltage drop across the resistor was/is sufficient to light
the IR Emitter diode and turn on the IR detector.

Of course, the IR detector turned on a larger transistor which triggered a
power relay which shut down the supply via an installed plug in ice cube
relay.  The entire circuit was built in the power supply on a small perf
board.  All components bought at radio shack.

K2WH 

-----Original Message-----
From: hallicrafters-bounces at mailman.qth.net
[mailto:hallicrafters-bounces at mailman.qth.net] On Behalf Of Mike Everette
Sent: Wednesday, November 16, 2005 2:01 PM
To: Charlie; hallicrafters at mailman.qth.net
Subject: Re: [Hallicrafters] Calling SR-2000 "Hurricane" Hams

This is good advice for operation of ANY power grid tube.  ALWAYS monitor
the screen current.  The same thing happens in G-E and Motorola VHF 250 watt
stations.  If your screen current runs too high, you are going to severely
reduce your tube life.

73

Mike
WA4DLF

--- Charlie <pincon at erols.com> wrote:

> Hi John.
> 
> Take a hint from a former NCL-2000 owner (also uses a pair of 8122's)  
> Watch the screen current as an indicator of tank resonance.  It will 
> peak when tuned.  Start with light loading and keep cranking the load 
> control up to lower the grid and screen current, until the proper 
> plate current is reached with safe screen current.  If it's anything 
> like the National amp, it's a very simple and smooth process.
> 
> 73' Charlie k3ICH
> 
> 
> ----- Original Message -----
> From: <W4AWM at aol.com>
> To: <w5uw at sbcglobal.net>
> Cc: <hallicrafters at mailman.qth.net>
> Sent: Wednesday, November 16, 2005 11:21 AM
> Subject: Re: [Hallicrafters] Calling SR-2000 "Hurricane" Hams
> 
> 
> > Hi Red,
> >
> > A friend of mine, Jon, N3AJB near Harrisburg, PA
> recently got a pair of 
> > them
> > and is frequenly on the air with one.  I just
> recently got one and am 
> > going
> > to recap the PS before I check the rest of the rig
> out.  I think the rig 
> > works,
> > but not positive.  I am looking for some spare
> 8122s, just in case.  Jon
> > tells me the rig is a bit tricky to tune up and
> the screen current has to 
> > be
> > monitored carefully.
> >
> > I don't have a lot of time to operate, but will be
> on playing with the rig
> > when I get it going.
> >
> > Jon says he loves to tell folks he is running
> "barefoot."
> >
> > 73,
> >
> >  John,  W4AWM
> >
>
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