The illusive µ726C transistor array

[Technician Larry]

Moog Sonic 6 uses a µ726C transistor array in the exponential converter circuit. Also used in the redesigned Mini VCO circuit. I have one used one in my parts drawer so I know they used to be available from somewhere. Senso does not list it @ Vintage Planet, and no search string of any sort turned up any useful info. Anybody know anything about this? I can't even find a spec sheet. Did this part disappear from the face of the earth?

I searched this forum and found several mentions of the 726, but no leads on procuring them.

[Technician Larry]

I just discovered that most of my problem locating info was that I was using the correct(?) character Greek letter mu (µ) instead of u in the search string. Still - seems like a search for 726C without any prefix would have resulted in a clue, but apparently did not. The only place I see these for sale is on ebay and all sellers are from Asia somewhere. Also I see some posts about "fake" parts, but the content accuracy of those posts is questionable.

Maybe it's just that my brain is fried from a marathon Sonic 6 repair session over the weekend. I have two of them here and they both had a dozen or more issues. One of the more interesting problems to trouble shoot was that (on one unit) both the X and Y mod generators did not perform correctly on the square wave setting. Other waveforms were fine. This unit has had the board interconnect hard soldered, and there was a solder bridge between pins B14 and B15. These pins are X TRIG and Y TRIG. Those trig lines are also the square wave output to the mod destinations. Being shorted together, square wave mod signals were inter-modulating, but the two triggers tied together caused no other immediately obvious problems. That took me a couple of hours to figure out.

One of the Sonic 6 units still has a VCO A that does not track over more than a couple of octaves - it then goes WAY out of scale. This unit was brought to me by one of my technician students who had taken my used uA726C and installed it in this circuit. The one he removed was likely OK as I found other problems in that circuit causing no VCO A output. I have a vague recollection that I may have kept that used 726 in stock because it worked "sort of" and I had no others in stock. Student mentioned will be returning the original 726 tomorrow and we'll swap it out again, though I never like installing used parts. I must have had a reason for keeping the one some years ago.

[thealien666]

I have seen some of them identified as 5J772631 or FU5J772631 before...
As seen here (the guy bought them off eBay, and no it's not me ):

[Portamental]

My synth tech has some, how many do you need ?

The original moog parts has FUA 726HC 7822 printed on them.

[Technician Larry]

My synth tech has some, how many do you need ?

The original moog parts has FUA 726HC 7822 printed on them.

I'd like to have a couple of known good new parts in stock for future use, and I may need one for the project on the bench right now. I haven't needed one of these for years, so it's not like I'm stocking up 741s or something. Apparently the ones on Ebay check out OK, but there was that one report that indicated otherwise.

BTW, the numbers 7822 likely indicate a date code - 22nd week of 1978.

[Portamental]

BTW, the numbers 7822 likely indicate a date code - 22nd week of 1978.

I got some of those, but they are totally ruined from spending 30 years in foam.

Original part is Fairchild uA726C. I got a crappy tech sheet for it.

My tech's are well stored parts. I'll get back to you on that.

[Kevin Lightner]

I have some also.
They're used in all sorts of synths- Early Roland SH series, Sys700, Polymoogs, on and on.
Just don't buy any off Ebay from Hongkongsuperseller.

[Portamental]

There goes my own little stock of 726's and 723's, totally ruined from spending 30 some years in their original foam packaging (Polymoog Road Kit). The other IC's in the kit I think are allright, a bit of scrubbing of the legs should do.



Now, what would a modern and easy to find foam replacement (with the proper characteristics to store IC's) to repackage the kit?

I do have some strips of "Elapor" foam, that is similar to foam from those foam spaghetti noodles used to float at the pool. Would that be suitable?

[MC]

"FUA 726" translates to Fairchild UA726. The "F" would be their logo.

Unfortunately there are counterfeit 726s out there

I can't think of a synth they can be scavenged from that doesn't have high market value

[Kevin Lightner]

A note from the Minimoog service manual:

"Minimoog between serial number 11362 and 11794 may have 726 integrated circuits from date codes 7850 and 7907 which will not hold the instrument in tune.
These devices should be replaced if found with parts of dated codes prior to or subsequent to these date codes."

[Kevin Lightner]

"The illusive µ726C transistor array"

Not nit picking, just a fwiw:

illusive
adjective
deceptive; illusory


elusive
adjective
difficult to find, catch, or achieve

[thealien666]

illusive
adjective
deceptive; illusory

Wouldn't that word apply to some of the counterfeit 726 chips found on eBay ?

[MC]

It's not nice to offend SuperSpellingMan

[Kevin Lightner]

SuperSpellingMan was fine.
But UsageMan took a long lunch.