[ARC5] OK Smart People - Mystery 211s

[Richard Knoppow]

     Its possible the Eimac tubes have a different kind of 
filament than the other tubes.  The reactivation works on 
thoriated tungsten filaments. I have not looked at the 572B 
to see what kind of filament it has.

     As far as getter, some transmitting tubes appear to 
have the same kind of getter as receiving tubes. I have 
somewhere a pair of very old Western Electric 211s that have 
the typical silvery deposit on the inside of the envelope. 
They glowed quite nicely when tried in my BC-375 perhaps 
forty years ago and were kept for display.  The other 211s 
all had plain envelopes.  Eimac used materials for plates 
that did the gettering when they were really hot.  Those 
tubes were designed to run so that the plate glowed.  I 
suspect if something has allowed air to get in the gettering 
will not work before the filament is poisoned.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com


----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: "Neil" <neilb at ihug.co.nz>
Cc: "ARC-5 Radios" <arc5 at mailman.qth.net>
Sent: Friday, June 15, 2012 6:58 PM
Subject: Re: [ARC5] OK Smart People - Mystery 211s


> On 16 Jun 2012 at 10:35, Neil wrote:
>
>> > Surely this will lead to severe grid damage?
>>
>> Might: depending on the tube.
>>
>> Ken W7EKB
>>
>> Ken,
>> I'm not sure if your original post was meant to be a 
>> tongue in cheek
>> way of disposing of a tube that had resisted all attempts 
>> to
>> rejuvenate it, but for those unfamiliar with tubes, be 
>> aware that
>> making the grid DC positive with respect to the filament 
>> or cathode
>> virtually guarantees destruction of the grid.
>
> No. It was not "tongue in cheek". It has worked quite well 
> for 572Bs....BUT
> one must be VERY careful when doing it!!!!
>
> Thus 45 VDC, NOT 2100 VC or even 1250 VDC (211s) on the 
> anode.
>
> In fact, this method would probably work just as well if 
> the grid were
> connected to the filament instead of the plate.
>
> Connecting the grid directly to the plate in a triode was 
> done in the past,
> although most certainly not as a matter of course.
>
> As an example (although this was NOT done with a LARGE RF 
> power
> triode!) in the Heathkit C-3 condenser checker, the grid 
> is connected to the
> plate and the tube, a 1626 power triode, is used as a 
> rectifier at 500 VDC
> output. I have taken such 1626s after they have been used 
> there, and
> plugged them into an ARC-5 transmitter, where they are 
> commonly used as
> a VFO tube, and they worked just as well as a new tube. 
> The grids were
> never damaged.
>
> In fact, I wrote an article for Electric Radio magazine 
> some time ago on the
> restoration of the Heathkit C-3 so I am VERY familiar with 
> that particular
> tester. I have two here and use them regularly.
>
> I only suggested this method as a POSSIBLE way to 
> reactivate the 211s,
> having never yet used it on a 211.
>
> I think it would work very well if proper precautions were 
> taken.
>
> If one was worried about grid dissipation, then a 
> milliameter could be
> connected between the grid and the plate, the current or 
> current-difference
> could be monitored, voltage measured, and PD calculated.
>
> I don't see a problem.
>
> Ken W7EKB
>
> P.S. All modern 572Bs I have tried to reactivate so far 
> have proven to have
> VERY "iffy" filament reserve: say, little to none. I have 
> used any of several
> methods. None were satisfactory. 304TLs and many of the 
> older power
> triodes had/have filaments with tremendous reserve 
> capacity.
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