[ARC5] OK Smart People - Mystery 211s

[Geoff]

----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
Cc: "ARC-5 Radios" <arc5 at mailman.qth.net>
Sent: Friday, June 15, 2012 11:21 PM
Subject: Re: [ARC5] OK Smart People - Mystery 211s


> On 15 Jun 2012 at 19:09, Richard Knoppow wrote:
>
>>      Its possible the Eimac tubes have a different kind of
>> filament than the other tubes.
>
> Yes. I am sure they do. They are usually either quite thick or 
> spiral-wound, or
> even made with little "fins" on them. For instance, the 304TL filament
> requires 5 volts at 25 amps, or 125 watts (or 10 volts at 12.5 amps). This 
> is
> substantial.
>
>>  The reactivation works on
>> thoriated tungsten filaments.
>
> As I understand it, the method I mentioned (2.5 x the rated filament 
> voltage
> for 1 minute, etc., ) ONLY works with thoriated-tungsten filamented tubes.
>
> There is a different method that works with pure tungsten filamented 
> tubes,
> and yet another method that works (sometimes) with rare-earth-coated
> filament tubes. Most of these last are receiving-level tubes though.
>
>> I have not looked at the 572B
>> to see what kind of filament it has.
>
> Thoriated-tungsten. But it is very thin and has no real reserve. The 
> filament
> in the 304TL, for instance, is quite thick and spiral-wound.
>>
>>      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.
>
> Both my WWII vintage 211s have a silvery coating inside the bulbs.
>
>> 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.
>
> Undoubtedly true. The various Eimac tubes have coated plates (I cannot
> now remember what that coating is: perhaps zirconium) and are designed,
> purposely, to run with lots of plate color. We ran our 304TL-modified BC-
> 610s with yellow-hot plates in Class B, which was undoubtedly over their
> normal ratings. But they were quite reliable. We never had to change one.
> Besides, it was SSB, and very cyclical.
>
> I remember one 304TL we had in a modified BC-610 that we accidentally ran
> so hot once that the coating burned off a large spot on one of the plates,
> leaving a large shiny spot there.
>
> The tube still worked quite well for several years afterwards.
>
> Ken W7EKB


You can also shut off 2 of the 304TL filaments and run as a 152T at 3dB 
down. Its really 4 75T's in one envelope.



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