[ARC5] OK Smart People - Mystery 211s

[J. Forster]

I you try to degas a tube in a hurry, ie with large currents, the positive
ions poison the cathode and kill the Gm.

-John

===============


> 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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