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Post subject: Re: Archeology of the Alamo Futura with schematic
Posted: Mon Oct 24, 2016 6:08 pm
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Rock Star
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TimsAudio, you are welcome! Lot of different circuits used in the heyday of tubes. I always wondered why Organ amps (like Conn and Leslie) used voltage regulator tubes on their screen supplies or anode plates. And not zener regulated circuits.

All I know, if you pull it --- the organ sounds terrible. Lots of bass distortion. Luckily, I've never had to replace one (OC3). They are tough cookies.

http://bentonelectronics.com/servicing- ... amplifier/


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Post subject: Re: Archeology of the Alamo Futura with schematic
Posted: Mon Oct 24, 2016 6:55 pm
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Zeners can be unreliable where there are big inductors around. A reverse polarity can destroy them in an instant.
They are the bane of vintage British motorcycles. If you hook up your battery reversed for a split second, it completely shorts out the charging system. Big inductors can probably do the same.
The OC3 is a reliable circuit and thats what an organ needs.


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Post subject: Re: Archeology of the Alamo Futura with schematic
Posted: Mon Oct 24, 2016 8:03 pm
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Rock Star
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Yeah, that OC3 is rock steady. And doesn't add too much noise to unit. Later solid-state keyboard units had zener-transistor interfaces, which are not as good with wide fluctuations in voltage input.

A lot of hi-fi units use OC3 or similar VR tubes to control plate and screen voltages.


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Post subject: Re: Archeology of the Alamo Futura with schematic
Posted: Thu Nov 09, 2017 10:14 pm
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Sorry to bump an old thread with my first post... Did anyone save the schematic for the Alamo Futura before photobucket decided to break every photobucket link on the internet? I just got one of these amps and it needs some love. That schematic would be so helpful and I'd be forever grateful.


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Post subject: Re: Archeology of the Alamo Futura with schematic
Posted: Mon Nov 13, 2017 8:53 am
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Here you go. Though, this is NOT the manufacturer's schematic. So there maybe some variations.

Image


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Post subject: Re: Archeology of the Alamo Futura with schematic
Posted: Mon Nov 13, 2017 9:16 am
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BMW2002Ti wrote:
Here you go. Though, this is NOT the manufacturer's schematic. So there maybe some variations.


Thank you so much!


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Post subject: Re: Archeology of the Alamo Futura with schematic
Posted: Tue Nov 14, 2017 9:33 am
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Thanks Beemer.
My copy is on a crashed hard drive and photobucket is no help.
While they assured me I could access my own uploaded photos, if they had been accessed by a third party, I can no longer see them either.


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