On 2/12/2011 11:26 AM, Steve Hunt wrote:
Jerry,
I did get a quote from Omeg. Their part with the closest match would
have been 220k with a reverse log taper, the correct size spindle bush,
a genuine 1/4" spindle (not 6mm) and the correct length.
They quoted £5.25 + 20% VAT each. Minimum order quantity of 10, then
postage of £6.00 + 20% VAT.
That would total over £70, and the pin spacing and length would still be
wrong! So I'm sticking with the new linear pot I put in this morning.
I doubt the Omeg part would have had quite the same taper as the
original, anyway. Their normal log taper appears to be the simple
"Commercial" taper comprising two linear sections of different gradient
with a single break point; I guess their reverse log would be the same.
Probably achieved by laying down two different widths of resistive
material, or two different thicknesses, though that might leave a
perceptable edge about the middle of rotation.
Just when I thought the projects had stopped, my cousin asked me to look
over a Hallicrafters SX28 which he just bought on eBay. It's no hardship
- those glowing dials, the smell, and the sound of that push-pull 6V6
output stage are just magic :)
Watch out for electrolytics in odd places, like maybe a bias supply
created by a resistor in the plate winding centertap of the power
transfromer.
73,
Steve G3TXQ
And if you run a single tone long enough you can get the screens of the
6V6 to incandescent temperature which is probably not good for their
logevity.
Good to know the linear pot is a practical solution for the original.
73, Jerry, K0CQ
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