[Boatanchors] Tube Shields

[James Liles]

Hi Rob:

The IERC tube shield does touch the tube and some use fingers and others 
spring loaded plates.  Here is a case and point as to their effectiveness. 
The SR-2000/SR-400/SR400A and a whole plethora of radios use the 6AQ5A for 
an audio amplifier.  The SR-2000 specifically and most others run that tube 
to maximum parameters.  Shoot it with an infrared temperature probe and you 
will find it at 420+ degrees and mean time to failure fairly short.  A great 
odometer or hour meter for the SR-2000 is the degree that the relay next to 
the 6AQ5A is charred.  Install an IERC shield and the tube will true out at 
270 degrees and you won't have to replace it again.  There are two switching 
circuits in the SR-2000/SR-400/SR-400A that use the 6AQ5A cathode potential 
to perform gating: the heterodyne oscillator to the transmit mixer and 
balanced modulator to the second if amplifier.  They expect +1.5v and +16.0v 
and if the tube cannot make at least 14.0v the receiver will provide you 
with a myriad of new birdies and deteriorated performance.

Antique electronics supply has the various sizes and configurations at 
fairly good prices.  Note:  You don't have to replace the tube socket: they 
also have the sleeve to mount it on the existing socket --- just drill the 
rivets out and install the sleeve over the tube socket.

Kindest regards Jim K9AXN


---------------- ORIGINAL MESSAGE -------------------

Message: 9
Date: Sat, 26 Nov 2011 06:27:22 -0600
From: Rob Atkinson <ranchorobbo at gmail.com>
Subject: Re: [Boatanchors] WTB:Tube Shields
To: Boat Anchors List <boatanchors at mailman.qth.net>
Message-ID:
<CALWD7Z5SRD=MQnT2aK=X4Xne8XSST-0fF240t=ytrVn90Q0Kmw at mail.gmail.com>
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There's an article in the Nov. ER that says tube shields are a bad
idea unless they are one specific type that sinks heat from the glass.
I think the IERCs are the right kind but don't hold me to that.  I
looked at mine in my 75A-3 and they were just spring loaded cans that
didn't even contact the glass so I pulled them out.  gg to see if the
rx works differently.  if not I'll leave them off.  Another type that
are no good are those metal wrap arounds usually found in old consumer
tube gear.

73

Rob
K5UJ

On Fri, Nov 25, 2011 at 9:06 PM, Doug DeWeese <ddswl at centurytel.net> wrote:
> Does anyone have any extra IERC tube shields? If so I need two for 9 pin & 
> three for 7 pin tubes. Please e-mail me direct with price delivered to 
> 97386.
> Tnx----Doug W7LNB
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