question on audio taper variations

[dadroadie]

Good Afternoon,
I have been donating my time and parts over the shutdown in repairing one of our local high school’s amp, a Fender Ultimate Chorus. One of the issues is one of the treble control shafts is broken off. I had thought I had a pot that I could take the shaft out of (thanks to Enzo’s help on the shaft question!) but when I opened it today I found that the shaft is staked and can’t be used as a donor.

The broken pot in question is a (50k 15A Taper) which is selling for $7.00 -$10.00 dollars plus shipping. I was wondering what the difference between this 15A taper pot and a standard 50K regular audio taper is?

I have one of these in stock and would save me the expense of buying one. I talked to the teacher and they said if the control worked similar to the way the old one did that was ok. Any help would be greatly appreciated!
All the Best!
Dad roadie

[dmeek]

Here are some charts of tapers. 15A is pretty much standard audio taper.

https://music-electronics-forum.com/...1&d=1588017862

[Leo_Gnardo]

Fender's been asking some princely sums for certain replacement parts lately. So I discovered when I needed to replace the mid pot on a Blues Junior. $6.95 for a super cheezy made-in-China pot that must have cost all of a dime to manufacture? Wow.... well I had to buy a bunch of parts from CE/Antique anyway so I bit the bullet and bought two. An extra so I'd have one in stock - eventually someone's going to need one & I can save them the wait. In your case I'd "go with what you got."

The 15 in the number refers to 15% of total resistance when the pot is at half-turn. If some super tech ran a set of curves on the amp's overall response comparing the 15A pot with whatever random audio pot you have on hand, sure they could show some slight aberration in response. OTOH if the amp's user twists the treble knob up & down, hears a difference as they move it, parks the control at a setting that's pleasing to them, then you won the game.

FWIW "audio taper" covers a lot of curves, sure isn't the same from one manufacturer to another, and isn't the same from one run of pots to the next. Maybe expensive hi fi manufacturers can order - or select - pots that have their specified curve. But at the amp repair end of the game, we have to deal with whatever we can find, especially so when dealing with PC mounted pots with particular bushing lengths and non standard shafts like D shape, splined, miniature (less than quarter-inch.)

[Enzo]

All the way down is zero, and all the way up is all the way up. The taper just sets what goes on in between. It wants 15%, and you have only 30% say? SO what, All that means is the amp will be at 4 on one amp where it would have been 5 on another. I never set volume by numbers anyway, I turn teh knob until it is as loud as I desire.

[g1]

I think I have swapped out the wafer in those 'staked' shaft type, if it's the type I'm thinking of with the white plastic wiper assy.
You do have to be very careful though, to get the plastic off and snap it back on again without cracking it.
It's been awhile, so I may be mistaken.

[dadroadie]

Thanks to everyone that helped me out on this!
The knowledge that all of you freely share is appreciated by me and I'm sure many others.
Stay Healthy!!
dad roadie

[Enzo]

I have in a couple emergencies put the white plastic wafer back on a shaft, and a little judicious application of my soldering iron tip melted the plastic back around the little barbs.

[dmeek]

Sometimes the shaft will pull out when trying to pull off the knob. Seems to happen to me mostly with Marshall amps. I just de-solder and
disassemble the pot, snap the plastic back on and it's good 'till the next time someone tries to pull that knob off. Maybe put a little oil on the splines