Baldwin Organ blocking osc tranny info

[Rob Mercure]

Howdy Folks.

Well, I've had the guts from a late 50s/early 60s Baldwin organ in my attic for almost 10 years - a friend found 'em at curbside sans cabinet/keyboard. And I later found a complete identical organ which is sitting on my front porch waiting for someone to buy it.
Being of a curious mind <grin> I eyed the blocking oscillator trannies from the organ guts and wondered if I could use 'em for other projects - they basically look like a small interstage coupling tranny with similar DCR (haven't done any impedance research yet).
Can anyone provide me with a sample schematic of how these were originally wired in circuit? Every google seach finds lotsa Baldwin schemos for sale but I just want to see how these things were originally used.

Rob

[MBSetzer]

I thought these things were tunable-core chokes, each one custom wound for a particular frequency, each paired with a corresponding custom-value precision capacitor, in self-oscillating triode circuits.

At least that's what it looked like to me, can't recall if what I saw was a Baldwin though, I was looking at hardware not a schematic myself.

If so, it seemed offhand like they would be relatively high Henries with low DCR.

while I'm here, there is an interesting link about custom winding coils:

http://www.ee.surrey.ac.uk/Workshop/advice/coils/

Mike

[Rob Mercure]

Mike,

This organ's tone generators consisted of two notes per subchasis - G and G# for the one I've got in my hand. Either tone used a larger oscillator tranny with a primary DCR of about 200 ohms and a secondary DCR of around 600. The single secondary winding has a cap soldered to one side - the cap positioned under the paper tape over the tranny windings. So there are two primary leads and three "secondary" leads - the two plus another that leads to the end of the cap that isn't soldered to the coil. There is also a trimmer cap for each note connected to the secondary leads.
Then there is a "bank" of other similar smaller trannies - four per note - that are wound on a common core - imagine the "E" of an E/I tranny having 9 "horizontal" "bars" (as the E is presented on a text page). Each of these is stamped "48, 49, 50, or 51" which I assume produce the octaves (each tranny's windings being smaller than the "main" ones). All together each subchassis uses 5 12AU7s.
So this circuit uses variable caps for fine tuning and I suspect that each subchassis's two "master" trannies are wound differently for each note.
I'm too lazy to trace out the circuit for each subchassis so I'd love to see how the oscillator and frequency multiplier (divider?) circuits are designed. And since I suspect that there is little call for the parts in the salvaged organ chassis I wonder if I can use these trannies for frequency tailored interstage coupling - either directly or in a NFB loop.
Just trying to find a use for as much of my "junk" as I can.
Rob

[Enzo]

For the 12 notes of the scale, each one starts with a master oscillator, which is then divided down multiple times for the octaves. Your "IF" transformers are just tunes circuits for those oscillators.

Visit www.mitatechs.com for resources. If you want a manual for the thing, ther should be a resource on that site. That is the MITA site.

[Rob Mercure]

Enzo,

I was a MITA member about 5-6 years ago and am aware of them. But I really don't want to purchase a service manual - I just want a representative circuit for the basic oscillator and frequency multipliers/dividers. And I'm curious about the how they obtained their "voices." You can either start with a sine wave and "dirty" it up with harmonics or you can start with a harmonic rich source and filter.
The subchassis is fairly well crammed and this is one of those "trace with a continuity tester" affairs - which I suppose I'll probably do eventually but I thought I dangle a thread and see if anything stuck in the meantime..

Rob

[Enzo]

Well, short of buying a manual, through contact with that group - potentially through a forum like this one - and especially if you mention your former membership - you might find someone who will just send you the part of the schemos you need. Or provide the tech explanation you want.

As far as I know, they start with clean sine waves. I'd hate to have to start dividing ugly waveforms and expect solid results a few octave lower. It is easy enough to shape it later.

And remember, the 16' of one note is the same signal as the 8' of the note an octave higher. And so on. All the sounds of a B3 come from the same set of bumpy wheels.