[Boatanchors] Check those filaments

[Rob Atkinson]

my line is also 122 v.  The only vintage gear I have that is
officially happy with that is the TO Keyer.  For some reason
Hallicrafters made it to run from 120 to 125 line v.

Rob
K5UJ

On Sun, May 16, 2010 at 7:28 PM, Ken Kaplan <krkaplan at cox.net> wrote:
> Just an fyi,
>
> I am refurbishing an old B&W model 600 GDO. You know - replace the
> electrolytics and the selenium rectifier. I decided to be thorough and
> measure the transformer voltages as no voltages are on the schematic. My
> line is about 122v. This gave a secondary voltage of 165v and a filament
> voltage of 8.7v. Hmm - the 955 acorn tube is speced at 6.3v for the
> filament. Perhaps that was why it glowed so bright. I put it on the
> Variac and set the primary at 115v and got 8.3v. I had to the drop the
> primary down to 104.7v to get 6.3v. Assuming the transformer is not
> fubar (looks & smells ok), I suspect those old transformers were not
> quite precision devices.
>
> I just stuck an 8 ohm resistor in series with the filament as the
> current is low. I don't think they are making 955s anymore. I guess the
> lesson is don't assume the filament voltage is right. In my case, it was
> 2 volts high with the correct line voltage. Yes, I'll make a note of
> what I did and stick it inside the case for a future owner.
>
> 73 Ken kb7rgg
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