Replace volume and input on circuit board

[jonjlw]

Hello, All - first time poster, here.
I am putting a guitar amp into an old 1940's Philco radio. I bought a cheap Class A tube amp with the hopes of using the components and making them work with the existing volume and tone holes in the radio. My problem is that the input and the volume control are hard wired to the circuit board. My question is: can I unsolder those and replace them with an input jack and volume control with wire leads? Here are pictures I hope that will help. Thanks for any guidance. Jon

https://www.evernote.com/shard/s159...9b1fd909a616/8442605badbcb8fd333b25c874aa5ce2

https://www.evernote.com/shard/s159...245b879b9027/8060a968eac11a0fcc7914257cf4443b

 

[davenn]

hi there Jon
welcome to the forums

your pics are not showing, make sure your links are working

Dave

 

[jonjlw]

Thanks, Dave . Just edited my post. I think they are there now

 

[KrisBlueNZ]

Yes, that's possible. You should probably use screened cable to avoid picking up hum and noise, and keep the cables short. Use the screens to make the ground connections - that is, the "sleeve" contact of the input connector, and the fully anticlockwise end terminal of the potentiometer.

You can use a mono screened cable for the input connector, but you will need a stereo screened cable for the potentiometer. This can be two individually screened cables, or a single cable with two conductors inside a single screen. It doesn't matter which, but the latter type is easier to work with.

If you are providing a replacement socket and a replacement potentiometer, make sure the potentiometer is the same value (1 megohm) and the same "law" - logarithmic or "log".

If you add your location to your profile so we know where you are, we can suggest a supplier and links to suitable components if you want.

Good luck!

 

[jonjlw]

Thank you, Kris. Very helpful. I just updated my profile. I live in Franklin, TN...about 18 miles south of Nashville. Thanks again! Jon

 

[KrisBlueNZ]

It looks like there's a Radio Shack in Franklin. They have a 50-foot roll of stereo screened cable which MAY be suitable - see http://www.radioshack.com/product/i...ce=CAT&znt_medium=RSCOM&znt_content=CT2032227

Small quantities of audio cable are apparently a bit of a niche market - nowadays most cables come fully assembled. You could also buy a short, fully assembled cable and cut it up.

I didn't have much luck with the Radio Shack web site. You might be best to go to the store and see what they have.

Here are some links to suitable parts on the Digikey web site. Digikey sell by mail order but their shipping may be quite expensive. But at least you will have references to suitable components.

Jack socket (enclosed style): http://www.digikey.com/product-detail/en/112AX/SC1316-ND/1217815
Jack socket (open style): http://www.digikey.com/product-detail/en/12A/SC1089-ND/109527
These jack sockets have three connections. The "switch" (or "normally closed") and "sleeve" contacts should be connected together and to the screen of the wire; the "tip" contact should connect to the inner wire. This arrangement means that when nothing is plugged into the socket, the input will be shorted to ground so it will not pick up noise.

Potentiometer (volume control): http://www.digikey.com/product-detail/en/1624154-2/A105789-ND/2363631

This type has the "side flat" shaft that suits a knob with a grub screw or the matching "side flat" shape. Digikey don't have any suitable potentiometers with splined shafts, which is the other common shaft style. For an example (NOT suitable for your application) see http://www.digikey.com/product-detail/en/P160KN2-4QC20B10K/987-1310-ND/2408887.

Of course you could re-use the original potentiometer.

 

[jonjlw]

Kris,

I think I have a local electronics parts shop in Nashville. Should be able to get what I need. What a great help you've been. One more question....what if I just used the same pot that I remove from the board. Seems like if I just put the proper shielded leads, it should work. Yes? What do you think.

Thanks again. Jon

 

[KrisBlueNZ]

Yes, you can do that. I added a note saying that at the end of my post, but you probably saw the first version of it.

You should also connect the screen to the metal parts of the potentiometer - perhaps solder a wire to the washer that goes round the neck. This will also ground the front panel, if it's made of metal.