Potentiometer D-spindle oddity

[BurningTantalum]

Recently I found a Fender 100W guitar amplifier left for dead on the kerb. I dried it out and it works well apart from the missing speaker.
 9 of the 12 knobs were missing and I had to replace a couple of pots. I ordered some knobs with grub screw fixing, but then realised that the flat on the original pot spindles is at the top (12 o'clock) when the pots are at mid-travel. This does not suit knobs with grub screws as the screw is at the bottom so that it is not visible. I had a look in my 'pot box' and the D-spindle type all have the flat at the bottom.
Are the pots unique to Fender/music equipment or have I just not noticed in many years of meddling that there are 2 configurations?
Regards,  BT

[MosherIV]

Recently I found a Fender 100W guitar amplifier left for dead on the kerb. I dried it out and it works well apart from the missing speaker.

This does not suit knobs with grub screws as the screw is at the bottom so that it is not visible. I had a look in my 'pot box' and the D-spindle type all have the flat at the bottom.
Are the pots unique to Fender/music equipment or have I just not noticed in many years of meddling that there are 2 configurations?

Are you sure it is the potentiometer or is it the plastic knob that is non standard?
I know Marshall make their own knobs for their amplifiers. No idea if they are inverted or not, should have taken up the offer from a friend years ago for some reject knobs from Marhsal 

Good luck 

[BurningTantalum]

It's definitely the pots that are non-standard (at least to all my other stock of pots).
Of course the knobs are the same too !  They have a skirt with numerals and a round hole with two small radial 'ribs' that allow for the flat of the spindle.
The pots have alloy spindles and the wiper is carried on a clear plastic disc. The disc is fixed to the spindle by a 'staking' process that spreads the alloy.
The pots look completely standard. Sorry no pics.
I just thought it strange that they were different for no apparent reason or advantage.

A pity that you didn't snaffle the Marshall original knobs- they are such a price new.
Looking at the Chinese replacements that come (conveniently) in packs of 10 or 12, the quality is atrocious. The printed numerals are all over the place, and the sellers don't even select well moulded examples for their photos. This is why I ordered grub screw knobs but I may have been better off with 'collet' type- I'm not bothered about keeping the amp original, in fact I have only a sheet of green Tolex to re-cover the case with !
BT

[CJay]

Work out where the grubscrew needs to be (screw it down on the shaft and see where it marks) then drill a shallow hole or file a shallow notch for it to sit in.