Board Mounted Pots in Preamp ??

[dumbassbob]

I have a 25 yr old Soho Quatro Guitar preamp,it has 4 12ax7 tubes,and was made in China It was first made in Germany by Kitty Hawk..The Master volume pot is bad and needs to be replaced..I do not want to burn the board...Can I just cut the bad pot off the board and resolder the new Pot to the old tabs?

[Enzo]

Not and have it reliable, in my view.

[dumbassbob]

Is there a trick to desoldering without burning the trace..

[Leo_Gnardo]

Is there a trick to desoldering without burning the trace..

Get in & out of there fast, with a hot enough iron. I use solder wick for this sort of thing, and the wick does some heat-sinking. Depending on the stickum used to hold the trace to the board, it may come unstuck fast or put up with a few more seconds of being roasted. Try as we might, even the best techs sometimes have the trace come loose. Rev up your iron, choose the appropriate tool to grab the pot leads & go for it. Worst that can happen, you'll be patching up with bits of solid wire.

[nickb]

Get in & out of there fast, with a hot enough iron. I use solder wick for this sort of thing, and the wick does some heat-sinking. Depending on the stickum used to hold the trace to the board, it may come unstuck fast or put up with a few more seconds of being roasted. Try as we might, even the best techs sometimes have the trace come loose. Rev up your iron, choose the appropriate tool to grab the pot leads & go for it. Worst that can happen, you'll be patching up with bits of solid wire.

...and use some flux on your solder wick. It makes things go so much better. A flux pen is very convenient for this.

[J M Fahey]

You might take the in-between road:
1) snip those pot legs off, so pot body is out of the way.

2) now it's way easier to pull stumps one by one (instead of having all 3 equally hot while having only just 1 solder iron and 2 hands) , by grabbing them one by one with long nose pliers and melting solder.
Since you will pull them straight up instead of wiggling (what *really* damages tracks and pads) PCB suffers the least

3) once you pulled them out, it's easy to perfectly clean the pad with solder wick or a strong solder sucker.
Wick is best

4) once clean of debris and solder , new pot legs will slide in easily.

Then follow standard soldering procedure.

I have replaced pots many times in same amp, with no problem, if being careful.

5) just in case, **practice** , solder any old broken pot you might have around to a piece of perfboard (the kind which has tiny round pads around each hole) and pull them back, even if you botch the first or second try it's non important stuff.

Work on the real amp only when self confident.

And good luck

[AmpFix]

Solder wick never really worked well for me. If you don't have a desoldering gun, the easiest method is to cut the pot tabs and remove them one at a time with a soldering iron and pump.

[dumbassbob]

Thanks, I only have a $15.00 Radio shack gun....Not the best

[dumbassbob]

I got the pot out,but now I do not know what kind or size it isIt is smaller than a guitar pot..all it said on it TO15A 250 Ohm Any Ideas? what I need..

[Leo_Gnardo]

I got the pot out,but now I do not know what kind or size it isIt is smaller than a guitar pot..all it said on it TO15A 250 Ohm Any Ideas? what I need..

Cool, now you're 1/3 done. Next 1/3 is locate the part. Smaller, probably 16mm diameter. 15A is audio taper, 15% commonly used in Peavey & Fender & lots of other gear. I'll bet it's 250K, not 250 ohms. Likely you can locate a similar or identical pot at Antique/tubesandmore.com with a shaft style to match what you took out, round, D-shaft or splined for push on knobs.

Mouser also has a selection of pots, but I'll bet you find it first at Antique.

Last 1/3 should be the easiest. Reassembly. Gonna feel good when it's done, right?

[dumbassbob]

Here my dumbass comes in ... It is a A250K...It is smaller then a regular guitar pot (Mini) I looked at Antique Audio 3 times and I did not see one... Maybe one one you can help me find the right one...The shaft is 13MM The full shaft and threds is 20MM ...Thanks again

[Jazz P Bass]

I abhore having to find replacement pots.

You have left out one key ingredient: The shaft type/ size. (so that the knob fits on.)

A few types that come to mind: splined, smooth, D.

[dumbassbob]

knurled? split shaft

[Leo_Gnardo]

Here my dumbass comes in ... It is a A250K...It is smaller then a regular guitar pot (Mini) I looked at Antique Audio 3 times and I did not see one... Maybe one one you can help me find the right one...The shaft is 13MM The full shaft and threds is 20MM ...Thanks again

Howsabout the diameter of the pot itself. The mini pots at Antique are 16 or 17mm. Yours is smaller than that?

Wouldn't be a bad idea to snap a photo of the control assembly you're trying to fix & put it up here.

[dumbassbob]

I am sure it is a 16MM on my $10 caliper it measured 15.61MM....