Saturday, June 11, 2011

Buchla 158A, 158B, 158 CBS versions

A thread in the DIY forum brings up interesting questions:

The CBS version up at Magnus' Buchla Page is extremely similar to the B version.

A version:

-All discrete, no opamps
-No uA726
-Transistors: MD708B (dual), 2N4916, 2N3565, U147, E101 (E101 is selected for =approximately= .5 Idss).

The E101 also appears if I remember correctly in the Minimoog oscillators, and the U147 also appears in the earliest versions of the Moog 901B oscillator.

B version:

-Opamps: LM302, LM301A, uA726
-Transistors: 2N4916, 2N3565, 2N4339 (Idss between .7 and 1.2), 2N4339 (Idss between .5 and .8).
-D1-D3 are listed as FD111 (???)

On the CBS schemo, note that some resistors are 1%, and some are specifically listed at 10%. These are at a glance, 1.0, 2.2, 4.7 multipliers, and include the 330K as well (which also appear in the sine shaper). Unremarked resistors are stated as being 5%. I note that the 258B schematic lists all 1.0, 2.2, 4.7 multipliers as being specifically carbon composition types, all others tin oxide. I wonder if you looked at a 158B/CBS/Tape Music Center unit if all of these would be Allen Bradley or other carbon comp.

As mentioned elsewhere, and thanks again to J3RK, the J201 transistor, easily available, has an Idss range which falls easily to .5 or so. I'd love to learn about the others and what would sufficiently replace them. The 2N4339 doesn't seem to dip down into that range very often; my batch go down to about .66 as a minimum. Useful for the 158B..

I note on the 158A part layout document (5Apr68) that there are a few bits not mentioned in the schematic:

-Note- "Plug in" version.
-R8 Sine: 1.5K; Harmonic: 680R.
-Add R34, (other notes, too distorted to read)
-No C7

There is a fat pen mark at the upper right, stating 158A-L.

I don't have the schemo in front of me so I have no idea of what "harmonic" means.