Allen 1800 (1500)(905-0086-? Capture Memory Power supplies

[John Kinkennon]

I'm enjoying this topic as I've reused these supplies for 4 of the 6 Allen consoles that I modified. One required repair and I had to reverse engineer the capture system to figure out how to operate the stops without the DM boards. One day I'm sure I will be confronted with the situation where I need to replace the power supply and I don't look forward to having to replace its function from scratch.

If necessary I'll pick up a modern power supply in the 45 to 50V range -- depends on whether we need the draw knob version or the one that drives the tab style SAMs. The 5V supply is nothing special so that will be easy. It is then necessary to switch the output of the big supply to a number of divisions plus the coupler rail which actually triggers off a pair of "N" inputs. Not a tricky design but probably something that would be built from scratch as has been mentioned. It will be a total pain from start to finish sourcing power transistors and the right heat sink, etc. Then there's is the need to make the beast safe by building a circuit that senses an output being on for more than perhaps 100 ms and shuts down the contraption. The PCB would take hours to lay out and probably $100 for three boards.

Being a hobbyist I'm not 100% practical with my time and might give it a try, but I'll have scoured every other possibility first.

[indianajo]

Moving AGO compliant organs is a serious ****. finding people that will give you one is even worse. They are advertising Wards Airlines spinets for $600 on e-bay now, notice? The Episc. church here got $500 from a member in a sister church for this Allen 301 that sounds terrible, has rattling speakers, and went totally silent in the middle of a service in October.
Figuring out logic is something I do in my sleep. I still do dream that stuff, since I enjoyed that job and noone will pay me anymore to do logic design the way Philco-Ford did. I could take the verbal descriptions in post 13 & 15, gin up a board in 74xx or 74HCxx logic familes in a week or two, including the driver transistors and heat sinks I have in my supply box and junk pile. I even have the 48 v 50 amp supply, something I fished out of the trash when they were scrapping out a lab next door. Probably need new e-caps by now even though it was a Lamda, the best you could buy in 1975. Then checkout. Did the description reflect reality? What happens when you plug it up? I enjoyed that stuff, too. Doing some now on a 1975 hifi amp that people nominate as "the worst amp ever built". Ha, the Schober one was worse.
Typical of Allen to build their logic into something doomed to failure like a power supply. They could have bought a Lamda for the money they charge for components, but then the money wouldn't go in their pockets. Success in business involves being crafty like that I suppose.

[John Kinkennon]

So going back to the original question, I'd suggest watching eBay for a couple of months while doing some creative searching. I've only needed to locate the capture power supply one time and was fortunate to find a fellow VPO enthusiast across the river in Portland who had one sitting around gathering dust. We did some trading and that was sort of a "take this if you want it" moment. I took a look in the garage myself to be sure but all I have is a few other types of Allen supplies.

[Dave Rivers]

Many thanks to everyone for the discussion! There's a lot of great information there! It makes
me hopeful that I can get the stops operable again!

I've been staring at the bottom of the console where I can clearly see where one power supply
would have been located, but I can't seem to find a location for a second one. Would it have
been possible for one power supply to have driven both DM-3 boards? The consensus seems to be nope...
but I'm just not seeing where the wires went... might simply mean more staring.

Also - I have a different question. How were the general pistons handled between the two DM-3
boards. Presumably for a Hauptwerk/MIDI set-up, I simply need to generate MIDI events for
the piston presses. But, I'm curious how the general pistons would have been routed to the
the two separate DM-3 boards. Would there have been some other circuitry for this (a relay or transistor
somewhere?) If so, would that need yet-another power supply?

- Many thanks! -
- Dave Rivers -

[tucsondave]

Are you sure they are both DM-3 boards with the same part numbers?
There was an auxiliary board used on larger consoles and only one capture power supply was needed.

td

[Admin]

I think it's possible that there was only one capture supply between the two boards. A single DM-4 (four division) board supports 128 stops with a single supply. OP's organ has around 150 stops. It's possible a single capture supply could handle the additional load, but I don't know that for a fact.

From the pictures, its clear that OP has two DM-3 boards. Allen did have a smaller auxiliary board along with a single DM board in some of the larger models, but it's purpose was to expand the number of pistons. It did this by sacrificing the dual memory capability of the system enabling the number of pistons to be doubled. The maximum number of stops controllable by the single DM board remained at 128.

In a two DM board system, general pistons would be wired to both boards with each board controlling it's own compliment of stops.

[John Kinkennon]

In one of Dave's photos one can just see the cut off ends to the wiring to a capture power supply. In the same area there is a label "Capture 2". Where a power supply was mounted. So I'm thinking there were 2 capture power supplies.

[tucsondave]

Why am I not seeing any photos?
td

[Dave Rivers]

Oh - the photos are on my blog: http://vpoproj.wordpress.com

- Thanks! -
- Dave Rivers -

[Dave Rivers]

Well - I braved the cold garage floor yesterday to get a good look at the bottom of the console.

Definitely two power supplies...