Kay K-503 Combo

I believe it is a '61 model, one channel, basic controls vol, tone, but has 3 inputs! Just a fun tube practice amp.

After all the mods sounds great. I've played through it with a couple of stock Strats and a Gibson semi-hollow body, makes great vintage blues sounds. Breaks up a bit at high volume level and agressive picking.

Considering it's a 47 year old amp and it powered up and made guitar sounds the first time I turned it on, I'd say it's pretty reliable. The mods make it even more so.

I think my mods voided the warranty :-).

The only markings on this amp is the 'Kay' brand badge. No model number (like most have on the lower right control panel) no inside schematic or parts list like some have found. But from extensive research from photos I have seen of other Kay amps I have concluded this is a 503, but I can't say if it is an A, B, C, etc. It does have a power isolation transformer, but the tube heaters bypass it! This, along with a non polarized 2 wire plug and no fuse made this an unsafe amp. So I just had to mod it! I recently finished completely gutting it of all but the fixed resistors and the transformers. Replaced all the caps with Orange Drops and Sprague atom electrolytics, pots were scratchy so changed them out, hated the tone power switch so replaced it with a regular 1Meg tone pot and added Carling power and standby switches while I was at it. Added a Fender style jewel light, a fuse holder and converted to a grounded 3 wire power cord. The speaker was torn up (from rough handling, not from over powering it!) so had to upgrade to a Jensen vintage series 8 inch. And of course replaced all the tubes with NOS replacements.
OK, so now it's pretty safe. I would have to replace the power trans with another with the proper values AND a second winding for the heaters to isolate them too, so they are still direct, but they are now fused and properly grounded.
After all that, she sounds pretty good. Getting a little 60hz hum, but I haven't had a chance to get in and poke around and push a few wires around. I suspect this thing was probably a (light) hummer from day one, there is no shielding anywhere and power wires and signal wires are running all over each other in there. It's a late 50's design, all TRUE point to point wiring (not turret/eyelet board commonly referred to as point to point. It has absolutely no circuit board). It has a nice clean chimey tone that is neither Marshall, Fender, Vox or anything else I've heard from the era, unique sound all it's own and great at that.

I believe it is a '61 model, one channel, basic controls vol, tone, but has 3 inputs! Just a fun tube practice amp.

After all the mods sounds great. I've played through it with a couple of stock Strats and a Gibson semi-hollow body, makes great vintage blues sounds. Breaks up a bit at high volume level and agressive picking.

Considering it's a 47 year old amp and it powered up and made guitar sounds the first time I turned it on, I'd say it's pretty reliable. The mods make it even more so.

I think my mods voided the warranty :-).

The only markings on this amp is the 'Kay' brand badge. No model number (like most have on the lower right control panel) no inside schematic or parts list like some have found. But from extensive research from photos I have seen of other Kay amps I have concluded this is a 503, but I can't say if it is an A, B, C, etc. It does have a power isolation transformer, but the tube heaters bypass it! This, along with a non polarized 2 wire plug and no fuse made this an unsafe amp. So I just had to mod it! I recently finished completely gutting it of all but the fixed resistors and the transformers. Replaced all the caps with Orange Drops and Sprague atom electrolytics, pots were scratchy so changed them out, hated the tone power switch so replaced it with a regular 1Meg tone pot and added Carling power and standby switches while I was at it. Added a Fender style jewel light, a fuse holder and converted to a grounded 3 wire power cord. The speaker was torn up (from rough handling, not from over powering it!) so had to upgrade to a Jensen vintage series 8 inch. And of course replaced all the tubes with NOS replacements.
OK, so now it's pretty safe. I would have to replace the power trans with another with the proper values AND a second winding for the heaters to isolate them too, so they are still direct, but they are now fused and properly grounded.
After all that, she sounds pretty good. Getting a little 60hz hum, but I haven't had a chance to get in and poke around and push a few wires around. I suspect this thing was probably a (light) hummer from day one, there is no shielding anywhere and power wires and signal wires are running all over each other in there. It's a late 50's design, all TRUE point to point wiring (not turret/eyelet board commonly referred to as point to point. It has absolutely no circuit board). It has a nice clean chimey tone that is neither Marshall, Fender, Vox or anything else I've heard from the era, unique sound all it's own and great at that.