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The beastly beast Allen Organ C-3

Ya gotta love those open mounted selenium bridge rectifiers! I know, I know, they gotta be replaced. But they just look so much more business like than an unimposing silicon replacement..........

Dave
 
Brice, I saw that B3 photo, its the only photo of an early Allen that indicates that maybe the organ's speaker and amp were outboard as the Gyrophonic Projector.

I also just realised (after seeing your thread on audiovintage.fr) that the second chassis is labelled CARILLON, and not C-3, which may indicate the amp was from an elaborate organ/installation with multiple amps/speakers.

This antiqueradios.com link has a better photo of a C-3 amp in a Gyrophonic Projector:
https://antiqueradios.com/forums/viewtopic.php?f=13&t=302896

The el34world link on a Webster amp shows that they used Airdesign transformers, so I think the Webster manufacturing origin is still valid for this C-3.
https://el34world.com/Forum/index.php?topic=23689.0
 
Thanks Tim.

This picture of a real C-3 in a its cabinet is the real deal. Great.

Possible that the C-3 was designed by Webster, but I is not sure either.
I've seen some other organ chassis with AirDesign transformers which weren't made by Webster.
But the fact that early Allen Organ amp were stamped Webster indicates a high probability.

Thanks for the links.
Brice.
 
I would think the "Gyrophonic" arrangement really wouldn't do much, compared to the Leslie's variable swirl of sound being directed around the room, which would do a better job of simulating the spacial properties of a much larger venue.
 
I'd expect it would need baffles or something in there to block and un-block the speakers as they spin past for it to have much audible effect. Considering how everyone knows the Leslie and you never hear of the Gyrophonic, clearly one was less popular.
 
gadget73 said:
I'd expect it would need baffles or something in there to block and un-block the speakers as they spin past for it to have much audible effect. Considering how everyone knows the Leslie and you never hear of the Gyrophonic, clearly one was less popular.
Click to expand...
I understand Laurens Hammond hated the Leslie, I suppose because it wasn't "his"? He promoted his spring delayed tank reverb amp cabinet instead.
Hard to imagine a Hammond without a Leslie, or both cabs.
 
I love old quad 6L6GC amps. It seems like screen regulation was common on these -- I wonder if there's a reason? Maybe helps with stability or the screen current draw is just too high and variable for a simple dropping resistor to work effectively?
 
It allows for a large drop without a large impedance. If you need to drop the screen voltage by 100 volts, doing that with a resistor would make the screen voltage extremely variable from idle to full output.

using some close enough data from the 6L6GC datasheet, idle screen load should be pretty close to 7ma, at full output its about 38 ma. 100 volts / 0.007 amps means a 14.3k resistor. At 38ma, that 14.3k resistor is dropping 543 volts, which is more than the power supply can even give. Basically the screen voltage would drop to zero and the amp would do nothing.
 
Right, seems like it's that combined with operating in AB. In class A, the increases in one side's screen current draw are better balanced by decreases in the other side's. Makes sense as these were high-power amps designed to pump out their rated wattage for an extended period of time in sound reinforcement and music playback scenarios. They probably spent more time in AB than the typical hifi amp.
 
Correct. These were built with reliability in mind.
And Gadget is right on all points.
Then can work with 3, even 2 6L6 and still producing good sound as each tube is independent from the other.
Clearly a unique design.
They are my favorite amps, even against all others I have.
 
Yeah, that OPT design is really something else. I wonder what it would cost to have something similar wound today (and how difficult it would be to execute with decent performance).
 
Commercial duty amps are definitely designed with different goals. They tend to not make a ton of power vs their tube count just because they aren't pushing everything to the limit. Reliability was more important than squeaking an extra watt for bragging rights.
 
Just bought an absolutely trashed pair of these on Ebay. Someone hacked up the chassis and re-configured the circuit, including an all-new tube complement. Truly one of those mad scientist hack jobs probably done by a bored ham so they could use tubes from the junk box.

Not going to bother sorting through their work -- gonna take the iron off, scrap the chassis, and rebuild them from scratch. Very excited -- I've been looking for these since reading this thread. And, with all due respect to the original industrial Allen Organ chassis, it will be nice to have them in something new and good-looking. I have enough rat rod theater amps around.
 
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I am a bit tempted to eliminate the 6AU6 since my sources are all pretty hot. Could change the first amp and PI combo to a 6SL7 or another higher-gain triode to compensate. Probably will at least give it a try, since I'm likely to breadboard the front end anyways.

@Brice Curious if you recall the approximate sensitivity of the amp with the original 6AU6 pentode config and then with triode strapped.
 
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