Kustom 250 Amp Head Broken Push-button switches

[nevetslab]

52 Bill had commented on the main problem with these Kustom amps is the fragile Blue Push-Button Switches. Sure enough, after setting aside the Vox Beatle to open this amp up, there they were...both switches improperly mounted by Kustom, so repeated operation of the switches over the years caused the threaded plastic mounting bushing to break away. Why use a second lock nut when you can leave one off, since the mounting bracket was formed wrong....and just use the stength of the thin plastic to get the switch to be where you want it mechanically? So, all these years, these switches break one after another, and there is no direct replacement for them. That's good solid engineering, aiming to boost sales of replacement parts in manufacturing! Detroit has been doing that one for years!



I played with a couple tie wraps, to see if I could just hold it together long enough to slip in with lacing tape and spot-tie the switch back into place. But the mechanics of the switch is such that the only solution with these existing parts (can't buy replacements....all gone years ago) is to glue the plastic threaded bushing back into place, then build up the surface surrounding the switch body and the bushing, while disallowing any of the epoxy to seep back inside to kill the mechanics of the switch. So, I'm going to attempt bonding that threaded bushing on both switches back into place.

Then, add the second lock nut that SHOULD HAVE BEEN USED IN THE FIRST PLACE! That takes the stress off of the switch body!



Now, to see if this plan will work. First need to glue the bushing back into place, mating the two broken halves as they should align, and clamp it into place. Then, lay a bead of long-cure epoxy around the bushing/body to form a short boss and hope that will be enough to use the two thin lock nuts & thin ITL washer under the upper mtg nut. Those are the same thin 1/2' ITL washers I place under both sides of the fuse holders on current/recent Fender Combo amps, as the fuse holder is always loose! Will this plan work? The white plunger slips out of the bushing easily enough, it being accessible behind the mounting flange of the switch body. I'll have to wait until Tuesday, as the building here will be closed tomorrow.

The Second switch....is the Death Cap switch, so it's not really needed....but...can't leave a vacant hole in the panel, even though having a replacement switch on hand is tempting.

[Leo_Gnardo]

Had to work on a Kustom 250 guitar amp a couple weeks ago. Luckily both switches were still working OK. Are the square cutouts big enough to mount rocker switches like the ones on 80's Marshalls? I would hate to do away with those kool blue push buttons but if it's a matter of expedience I'd have no hesitation in mounting Marshall-style rockers.

[nevetslab]

Had to work on a Kustom 250 guitar amp a couple weeks ago. Luckily both switches were still working OK. Are the square cutouts big enough to mount rocker switches like the ones on 80's Marshalls? I would hate to do away with those kool blue push buttons but if it's a matter of expedience I'd have no hesitation in mounting Marshall-style rockers.

The switch opening in the panel is 16.2mm square, with the panel thickness there being 2.7mm. I don't recall the size of the 1980's Marshall rocker switches. All the ones we have in our inventory are much larger openings.

I now have the switch bushings glued and curing, each parked in a vise to wait for Tuesday morning. I thought about replacing the switches. I used to have Clare Pendar illuminated push-buttons switches from some vintage consoles. Switchcraft had similar expensive switches. Hopefully I'll have success on Tuesday...though the switch button surface will now be recessed a bit to accommodate the second mounting nut.

[Leo_Gnardo]

The switch opening in the panel is 16.2mm square, with the panel thickness there being 2.7mm. I don't recall the size of the 1980's Marshall rocker switches. All the ones we have in our inventory are much larger openings.

I now have the switch bushings glued and curing, each parked in a vise to wait for Tuesday morning. I thought about replacing the switches. I used to have Clare Pendar illuminated push-buttons switches from some vintage consoles. Switchcraft had similar expensive switches. Hopefully I'll have success on Tuesday...though the switch button surface will now be recessed a bit to accommodate the second mounting nut.

At 16.2 mm, I think it's a no go for the Marshall switches. I haven't one here to measure but they're about an inch square cutout. Hope your glue fix works! Time was you might have found switches to fit at a local surplus shop, maybe labeled "ARM" and "LAUNCH" for extra effect.

[Chuck H]

Just found this too:

https://www.mouser.com/ProductDetail...CABEgIGNvD_BwE

Requires a 16.2mm square mounting hole. Looks like the snap mount requires a specific panel thickness.?. (EDIT: snap mount will work for 1mm to 3.2mm) This one is amber. Not sure if blue can be had (EDIT: No plain blue but they do offer an amber/blue. So amber would be unit on and blue would be "feature engaged"?). Mouser doesn't have them in stock but it looks like Digikey might. I didn't check about the illumination voltage. It's LED so you might have to make a little circuit.?.

[nevetslab]

Just found this too:

https://www.mouser.com/ProductDetail...CABEgIGNvD_BwE

Requires a 16.2mm square mounting hole. Looks like the snap mount requires a specific panel thickness.?. (EDIT: snap mount will work for 1mm to 3.2mm) This one is amber. Not sure if blue can be had (EDIT: No plain blue but they do offer an amber/blue. So amber would be unit on and blue would be "feature engaged"?). Mouser doesn't have them in stock but it looks like Digikey might. I didn't check about the illumination voltage. It's LED so you might have to make a little circuit.?.

Interesting thought. I'll look at these switches, as in the future, if they do indeed fit, sounds like a good replacement. Only the Death Switch uses the SPDT function, while the power switch is SPST. The die-cast aluminum panel's thickness at the two square power / polarity switches looks too thick to accommodate the mounting clips, but will check that. Thanks for the suggestion...if they work, those who repair Kustom amps of this style will like to know about those. At any rate, my surgery on the switches was successful:



As I had eliminated the Death Cap that was attached to the Polarity Switch (next to the Power Switch), I also eliminated the AC wiring to that switch, so effectively, that switch is now a spare, should the power switch fail in the future. I thought about keeping it as a spare, but, didn't have a good solution for plugging up that square hole. When I got in this morning to see how the glue-up went, and took the time to chip away at the excess epoxy...which would allow the base nut to thread down as far as possible, the thought on the way home Sunday night, after having glued the bushing back into place, I realized then I should have threaded the base nuts down while the epoxy was still liquefied, No matter....it came out ok. The switch buttons are now further recessed due to Kustom's mechanical engineers spec'd the part's depth wrong. As a result, the face of the button is a little further back.



What was a bigger problem was the failure at Kustom to have finished the smoothness of the square openings. Both were very rough, and caused the button to bind, rather than operate smoothly. So, I had to spend time with a small flat file finishing the inside surfaces of those two square holes. Now the switch buttons don't bind, and the switches operate nice and smoothly.

I almost got screwed when I went to slip the white plunger into the bushing. The brass lamp socket didn't allow the fingers that mate with the rotary cam switch, so I had to cut away a tiny bit of that plastic, hoping I could get it thru past the socket. Lucked out on that one.....working smoothly.

I brought up the AC Mains slowly, power switch engaged, and watched the supply voltages and output voltage on the power amp as I walked the variac up, also watching for any sudden current surge on the power analyzer. All came up fine. Nominal supplies on this amp is +/- 40VDC, and DC Offset less than 20mV.

I need to clean the pots, as that has been the prime objective on all of these amps. No easy access to those on this amp, so more disassembly required to get at the large array of pots on this amp. At least the power switches are restored.

[nevetslab]

Having seen the amp power up, I connected my shop speaker to it, and went thru the controls, no signal applied, to see if any of them strongly objected to being rotated, or yielded loud noises or such annoyances. All surprisingly quiet, considering its' age. I then plugged in burst pink noise, to give a listen to both channels and the effects present in the controls. Everything works, though I never did hear the Vibrato work. Tremolo works fine. I didn't spend a lot of time searching for documentation to see if the Vibrato/Tremolo choice appears on the effects pedal which connects to the rear panel 6-pin XLR Female connector. The Selective Boost control, it being a resonant peaking filter, I would guess this works in kahoots with an expression pedal for a Wah-Wah kind of thing. Static setting on those Effects controls is not very useful. Fuzz works. All of the controls were quiet, which satisfied me, so I didn't have to pull all the PCB's out to get at the bottoms of the pots to spray them.

I did at least remove all of the control knobs and took those to kitchen for a good cleaning. When I moved the tuck-n-roll cabinet to the bench, I was staring at the white gaffer's tape label showing control settings from decades ago, I'd guess. Reluctantly I peeled it off, it leaving a nasty yellow gooey stain on the naugahyde covering below the knobs. I attacked that with Bestine and Denatured Alchohol, and that seemed to have removed the mess without leaving it sticky or stained.

Put the top cover back on, then slipped it back into the tuck-n-roll cabinet, and secured it with the long four chassis mtg screws. Set it atop the pile of working combos of Mike's, feeling somewhat relieved it didn't demand more effort than just the two Licon Switches selected for their amps. Actually a nice switch...clever cam-actuated push-push mechanism. First time I've seen these. One thing I never did find......where is the power supply rectifiers? I didn't see a diode bridge block, nor a pair of rectifiers, let alone four to make up a bridge rectifier.

Does anyone have the schematic for the amp, as well as the foot switch that mates with the 6-pin female XLR connector?