WTD: ~3K 3W B taper wirewound pot for tube tester

[Brenda Ann]

No problem paying $20-25 or so if someone has one of these puppies. I found
some nice 4.7K on ebay, but I hadn't realized that the one I need is audio
taper...

[dave]

Rheostat may get better results

[Brenda Ann]

"dave" wrote in message
news:F_OdnRVm9oUEhzTS...@earthlink.com...

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Has to be a WW pot. Rheostat won't work. Also has to be B taper. It's the
pot that adjusts what appears to be grid bias (though I could be wrong, I
didn't look that closely at the schematic.) It's the "R" control on an
I-177.

[William Sommerwerck]

> Also has to be B taper. It's the pot that adjusts what appears

> to be grid bias...

Is the taper to compensate for the non-linearity of the tube's transfer
characteristic (ie, make the plate current vary linearly with pot rotation)?

[Bill]

if it would help, I have a 5K ohm helipot (10 turn), marked "A", and
"MW", 3% resistance tolerance, .25% linearity tolerance, it's wirewound.

if you can't find what you want, why not use a little solid state
circuitry to do what you wish?

[nik tesla]

On May 6, 8:23 am, "Brenda Ann" <newsgro...@fullspectrumradio.org>
wrote:

> No problem paying $20-25 or so if someone has one of these puppies. I found
> some nice 4.7K on ebay, but I hadn't realized that the one I need is audio
> taper...

Hate to say it but that is a special pot wound only for Hickok, the
only thing that will work correctly is one from another Hickok tester.
Many models used that same pot. I think Roger Kennedy had some made up
specially for this. For example at full setting of 80 there is 40 vdc
but at 40 on the dial there is 11vdc and at 20 there is 3.5 vdc.

[zen...@verizon.net]

I got that wrong, it's Dan Nelson d...@ieee.org

[Sofa Slug]

Would it be possible to "fake" the taper with a linear wirewound pot &
some external resistors?:
<http://www.geofex.com/article_folders/potsecrets/potscret.htm>

[zen...@verizon.net]

On May 9, 12:42 pm, Sofa Slug <sofas...@invalid.invalid> wrote:

here is a thread about the subject
http://antiqueradios.com/forums/viewtopic.php?f=8&t=182836&start=20

[Bill]

it would probably be easier and more accurate to make up an EPROM, a 10
bit D/A and a 1024 count encoder (and if needed a counter chip). Count
the pulses (in quadrature, of course for direction), use the count as
the address into the EPROM, take the output of the EPROM to the D/A.
program whatever curve you want into the EPROM. Now you have your
nonlinear voltage from the D/A. Just use that as the ref voltage for a
standard forward pass regulator and you are done and it will never wear out.

[Brenda Ann]

"Bill" wrote in message news:jofde2$fio$1...@dont-email.me...

it would probably be easier and more accurate to make up an EPROM, a 10
bit D/A and a 1024 count encoder (and if needed a counter chip). Count
the pulses (in quadrature, of course for direction), use the count as
the address into the EPROM, take the output of the EPROM to the D/A.
program whatever curve you want into the EPROM. Now you have your
nonlinear voltage from the D/A. Just use that as the ref voltage for a
standard forward pass regulator and you are done and it will never wear out.

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Maybe for a digital engineer... but not for me. I'm still mostly old school.
I've done very little with analog IC's, and virtually nothing with digital
IC's. I still have one of those digital generator modules that anyone can
have for free if they want it... I have no use whatsoever for it, since I
haven't a clue how to build an interface for it. :-/