BUCHLA 100 CLONES CONSTRUCTION

BUCHLA 100 CLONES CONSTRUCTION

Buchla 165 Random Voltage Source

Here is a short video showing the 165 (top center) with the 2 sides triggered by alternating pulses from a 140, each side controlling half of a 178 (click on the image for a video).

You can clearly here the clacking of the relays as mentioned in the original Buchla literature. It's probaly worse here since there is nothing between the back of the module and the plaster wall behind it. I'll need to put some foam insulation around the relays at least.

The BOM calls of Q9, Q10, Q14 and Q16 selected for a high Beta (Hfe) value, and Q18 for a low Beta value ( < 160).

Q9 and Q10 are PNPs (2N2906) and needed to be > 200. All of the ones I checked had a higher Beta than that, so that was easy.

Q14 and Q16 are NPNs (2N3904) and needed to be > 250. I spent over a day checking a LOT of 2N3904's (I had over a thousand in my stash) before giving up. I opted to use 2N5172 transistors for these instead. My second big mistake was not verifying the pinout - turns out the base and collector are swapped on these, so I ended up desoldering them and putting them back in correctly.

Also finding a low Beta 2N2906 for Q18 (yes, I have over a thousand of them too) proved improbable, so I used PN3638A transistors for them.

My first big mistake was in wiring up the EDAC connector for the power - I wired it to -15V instead of +15V. I didn't see any smoke, so I didn't notice anything wrong right away - except that it didn't work.

The good news is that the only damage was to the electrolytic caps (C3, C10 & C11).