Potentiometer shaft extension

One of the challenges in turning an old tube radio into a cool guitar amp is setting up control knobs. It is common that old radio chassis is mounted inch or two away from cabinet's front panel. Re-using original pots is not always an option. Their nominal may not fit a circuit. The old pot can be noisy with no easy fix. Original pot might have a linear type, not very suitable for volume control. Finally, an old radio usually has one or two pots only; the other knobs are multi position switches and tunning knobs with a spool driving a dial cord. So you need additional pots anyway to fill those positions. As a result you have to find a way to install one or more brand new potentiometers with short shafts.  

First, I am going to list other options I tried before developing a final solution. 

Option one. Find enough old pots.

This is self explanatory option with all the drawbacks listed above. In my very first guitar amp I opted for this simplest one. On the pictures you may see a couple of pots with different color scavenged from a few old radios. Even though it worked well, I used all my pots on the very first project and had to look somewhere else for the next one.

Option two. Buy a long shaft pot.

This became a challenge right away. I wasn't able to find a proper option on Digikey, Amazon, or Aliexpress. The only one available was that Alpha pot with SPST switch from the Amplifiedparts. It has an impressive 40 mm long solid shaft and has two options: A500K and A1M. You can see two of those in my second project: Fender Princeton 5F2 clone. Having SPST switch on all your controls is a bit misleading though. Also, 40 mm of length is not always enough. Shipping from the USA is another pain in the amp nowadays. Finally, nominals available don't feet full tone control schematic which usually require 250K pots.

Option three. Use standard pots and move chassis forward.

The chassis is staying away form a front panel to give some room to dial driver and dial screen. With all dial components taken off, you can move chassis forward by drilling new mounting holes in a cabinets floor. I actually tried this on the second amp as 40mm wasn't long enough. Also, both wooden and Bakelite cabinets are not that very drill-friendly. 

Final solution.

One of the radio I repaired had a volume pot already replaced. New pot wasn't long enough, so the new shaft was extended with this thing:

This led me to a solution which consists of: 

• Brass pipe 0.25mm wall thickness OD 7mm x ID 6.5mm, 300mm. $6.39 on Aliexpress
• Brass round rod, 1/4x36". $24.44 in Homedepot
• J-B Weld HighHeat, two-part epoxy. $17 in Canadian Tire
• Had to build a stand so extension is well aligned 

You can see the idea on the next pictures. Pot's shaft and an extension made from brass rod are pushed inside a 1/2 inch piece of brass pipe, halfway each. Made a few dents on both shafts with file so glue can stick better. The stand grantees that product is aligned and has no offset when rotating. 

The extension works very well. It costs less than $1 per a single pot. Final product can slide through a nut and washer. Brass is durable enough to withstand a load when you press knobs back to the shaft. Below is one of my new projects with shafts extended this way.