[Boatanchors] Check those filaments

[Paul Kraemer]

I have 123v here at home and in the shop
Everything is happy. The "100w" output exciters and linears even have an 
extra boost.
Paul K0UYA

----- Original Message ----- 
From: "Rob Atkinson" <ranchorobbo at gmail.com>
To: "Ken Kaplan" <krkaplan at cox.net>
Cc: <boatanchors at mailman.qth.net>
Sent: Sunday, May 16, 2010 8:15 PM
Subject: Re: [Boatanchors] Check those filaments


> 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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