Vintage EHX boards pretty regularly had parts tacked on the back either because a PCB layout had a mistake, a design change was made or because they were out of a particular value so paralleled two resistors. So it’s probably an original resistor.

Well it’s a 5 x EH1048 version rather than the LM13600 version or earlier 6 x EH1048 version… that’s about all I can tell you on the model number, looks like a later run from the PCB.

It’s probably easier to just replace the switch, it’s an old switch anyway and mechanical parts do fail with age so even if you got it back together it might not last long.

I would just check the voltage for the country of purchase online but if you’re worried about the board, you can remove the 3 wires connecting to the board and test the AC voltage coming out of the transformer, the middle wire is your common and either of the sides should be about 18V. Unless there’s a part number written on the transformer to check which there wasn’t a lot of the time.

Assuming it doesn’t already have one, you should definitely consider wiring an earth connection to the pedal for safety’s sake.

The Small Clone does do for most of the sounds but Nirvana fans generally seem to be looking for the ‘Radio Friendly Unit Shifter’ sound from the Polychorus which a Small Clone wont get to.

I forgot they replaced the blend with the ‘sweep filter’ in exchange for out of phase outputs, never could understand why they decided to make that change.

I take it that’s the model with the MN3008 & MN3009 from the PCB Code.

The schematic only gives the clock adjustment;
Sweep Filter – Off
Width – Full CCW
Rate – Full CCW
Tune/Delay – Full CW
Mode – Filter Matrix
Adjust Trim 8 for 100uS at 4013 pin 1.

Trim pots 1 & 4 are your BBD bias and Trim pots 2 & 5 are the BBD balance trims, setting those up will be similar to any other BBD set up procedure.

EHX pretty regularly put components on the back side of the boards in the old days, i’ve seen other early small stones with that. They also switched up the silk screens now and then, by any chance does it look like this? https://i.ytimg.com/vi/MKK5ayYYPh8/maxresdefault.jpg

So yeah it’s an early unit but I wouldn’t say it’s an oddity.

As far as I know, none of the production units quite match up to any of the schematics (there’s about 4 schematic variations, all subtly different) it’s close enough for jazz but I wouldn’t take values from it.

Squealing with the feedback up is self oscillation and the reason a lot of effects with a feedback control have a trimmer inside to limit it before it reaches that point, that resistor was obviously added to limit the feedback to stop it oscillating so I still think it’s probably original.

Yeah the rate control goes in to ring mod territory and at a certain point the vactrols are too slow to keep up, with value drift over the years your rate range might not be optimal but it sounds like it’s working as it should.

All these vintage EHX effects were designed with the pickups of the day in mind which were mostly low output single coils, there’s a fair amount of gain at the front so with the addition of lots of feedback some distortion doesn’t sound like anything is probably wrong, but I couldn’t say with certainty without having it in person.

No, it wasn’t made for the ad, as I linked earlier, there’s another that looks the same and i’ve seen more over the years. EHX obviously at some point decided they preferred the later aesthetic so more were produced in that variation. I know you want it to be unique and worth more but i’m afraid it’s not.