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Pamphonica 11th Aug 2019 7:13 pm

Removing 1950s clear push-on knobs (Pam 710, Pye P123BQ)
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This "wanted thread" started me on trying to remove some knobs from a scrap set to help out the Black Country Museum. The very rare Pam 710 has the same knobs as the earlier versions of the Pye P123BQ, even though the Pam knobs are on the top face and the Pye knobs are on the front face.

Removal of these knobs was non-trivial, given their age and fragility, so here are some hints for those who follow...

The volume knob comes in one piece but is actually composed of a clear cover and a captive but separate inner with the "volume" and "off" legends. The inner is held captive and non-rotating by the shaft circlip.

This knob was removed by firmly wedging the knob up in three places, 120 degrees apart, overnight, then carefully easing off the knob by pressure all round the rim at one time (lots of fingers) the following day. The idea was to "encourage" the knob the come off by sustained but even pressure.

The dial knob is more complex - a very compact slow- and fast-motion composite. This must be removed one element at a time, clear cover first, then shaft alignment to allow the scale part to come off (see below).

After a lot of simple, all-round upward pressure, but to no avail, plan B emerged. This removal required very small holes to be drilled in the knob centre (normally hidden by the bright). The first hole, slightly off-centre was to introduce some Plus-gas to help free up the knob for a few hours. The second hole, in the centre of the knob, was to put a slim watchmaker's screwdriver through, to contact the top of the tuning gang shaft. This allowed some proper tapping downward while exerting upward pressure on the clear outer knob portion.

Once this clear cover was removed, the fast-motion shaft flat could be seen, and carefully aligned with the slow-motion portion of the shaft and the main dial section removed.

Don't be tempted to pull off both in one go, by the way. If the clear section (upper) shaft flat is not properly aligned with the bottom section flat you WILL definitely break the fragile plastic stem of the lower, scale section when you attempt removal. The scale section has a flat and that must slide properly over both shaft sections. You have to remove the top clear section first so you can see where the flats are. Even then it's a squint to see where the lower section flat is.

Job done, anyway, and maybe these hints will help someone.


Phil G4SPZ 11th Aug 2019 9:36 pm

Re: Removing 1950s clear push-on knobs (Pam 710, Pye P123BQ)
Many thanks Jeremy, both for offering the knob and for the detailed instructions on how to fit it! You obviously went to great lengths to help me and potentially many others, so thank you very much.

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