[sdiy] Moog 909 power supply component ID question

[Gene Stopp]

It is 1N821: 5.9 - 6.5 volt, 75ma, 15 ohms

Coincidentally I am in the middle of debugging a dead 910 power supply. I've
got an old old original operation and service manual, and I can see by the
datasheet for the 910 that it was designed in 1965! The difference between
the 909 and the 910 is the 910 has an extra output, which is -10 volts
unregulated which is only used by the 901 and 901b oscillators. It's
interesting in that the +12 and -6 bipolar outputs are NOT based on
center-tapped full-wave-rectified positive and negative raw DC sources.
Instead, the half-wave rectified secondary goes across a single big cap,
with the positive side being the +12 output, and the ground and -6 outputs
are controlled by the TO-3 pass transistors (Germanium PNP!). The negative
side of the big cap leaves the power supply first, going out to a DC fuse
and back in to the power supply. (Aha! This is why the thing doesn't power
up by itself on the test bench - you need to stick a jumper in the jones
socket.)

I am torn between three possible routes of repair:

1. Repair with new components

This will take some time, since I'm not too good at discrete transistor
power supply designs. This means I will probably use the "educated guess"
shotgun troubleshooting approach, using a scope to verify passive components
and replacing active components. The problem here is finding replacements
for 1965-era transistors. The advantage to this approach is that the 910
will remain essentially unmodified and "vintage".

2. Rebuild with new regulators in existing 910 chassis:

This means I will rip out the guts, leaving the chassis, transformer, and
all associated jones sockets. I would add a full-wave rectifier and big
caps, plus some new modern regulators mounted in the existing heatsinks. For
the +12 I would probably use an LM350 in a TO-3 case, and for the -6 I would
probably use an LT1033 in a TO-220 case. The -10 unregulated would come
straight off the raw negative DC. The advantage of this approach is that I
will feel a lot better about the power supply continuing to operate properly
into the 21st century. The disadvantage is that I would essentially destroy
a little piece of history.

3. Make a new power supply and shelve the 910

This would be the same design as #2, all new stuff, with a new chassis (or
block of wood) that fits into the same footprint of the 910. The problem
with this approach is that I would have to go out and find all of the 3-pin,
6-pin, and 8-pin jones sockets somewhere. That plus all of the metal bracket
fabrication etc. Then fixing the 910 would become a rainy-day project.

Questions to list:

Any opinions on keeping the 910 "vintage"?

Anybody know where to get all those jones sockets? I'll do a search, but
short-cut help would be great.

Best Regards,

- Gene



-----Original Message-----
From: Michael Buchstaller [mailto:buchi at takeonetech.de]
Sent: Wednesday, December 04, 2002 5:40 AM
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] Moog 909 power supply component ID question


Hello dear list friends,

for my 904A filter i have also built a clone of the original
909 power supply circuit.
I had tu substitute the germanium output transistors DTG110
with the more readily available ASZ17 - i think this should be
no problem.

But there is a Zener diode D6 whose value i cannot read.
(it may be 1N821, but i am not sure)
Which voltage should it have ?`

Thank you all !


-Michael Buchstaller