Reverse engineering a tube 50's Clavioline Synth hook up - diyAudio
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Old 6th June 2011, 06:32 AM   #1
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Default Reverse engineering a tube 50's Clavioline Synth hook up

Hi.

I recently purchased a Clavioline keyboard -these were sold from the late 1940's through the mid 1960's and are famous for being used on 'Telstar'. These came originally as a set with a small amplifier -usually a Selmer or Gibson- that, through a multi pin connector cable, powered the keyboard and carried the output signal to the amp. Unfortunately the keyboard I bought didn't come with the amplifier or cable so I have no way to power it and play it.

Here's what I need help with: I want to make a breakout box that will power the keyboard and use a regular 1/4" instrument cable to run the output signal to an amp. There are 4 tubes in the keyboard -a 6J7, 2 6SN7 GT's and a 6J5 -I am thinking this is the preamp section and wants 6 volts, so two of the pins provide this. Obviously there is a ground so a pin connects amp ground to keyboard ground. There's also probably 2 pins for the output signal. I'm guessing the 6th pin is for a tremolo or some other effect switching between the amp and keyboard.

So -anyone ever make something like this? Is there an off the shelf solution I don't know about? Any help is greatly appreciated. I took electric circuits a while back as part of my degree program but it's been a while and it was all diagrams and calculations...

Also, all the capacitors are 'Tiny Chief'. Are these likely the originals?

Pictures of the keyboard can be seen here: 823aaaaa - a set on Flickr
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Old 6th June 2011, 10:47 PM   #2
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probably 2 other of the pins provide B+ (high voltage) and power supply ground (chassis). You can determine what voltage this should be by looking the tube datasheets up on triodeelectronics.com website and keeping the voltage under the maximum. You can look for the B+ to connect through resistors to the plates of the tubes. You can look for the 6 VAC to connect to the heaters of the tubes.
From a capacitor attached to the plate of one tube, should be the voltage output. It might go through a level setting potentiometer, first.
People figure stuff like this out all the time hooking leslies up to organs. Some organs got the B+ from the Leslie, some vice versa, some the B+ was independent and the only links were AC signal, on-off, and 120 VAC.
Look in your keyboard to make sure there is not a 120 VAC to heater and b+ transformer. It would be near large capacitors (10-40 microfarad, mf in 1960) at B+ voltage, IE 300-400 VDC.
If you don't have a multigang cap near a transformer, you might have a single element 10 mf @400V cap for local B+ stablization.
You'll have to trace the circuit out, at least on the power side, to determine what you have. Expect any electrolytic caps, that is ones with + on one end or circles moons and triangles near multi-terminals (all plus) to be dried up and potentially explosive. The rubber seals deteriorate from oxygen and the water leaks out.
You might find an actual expert on electronics section of organforum.com. Andy and HandyCzech have sold about every keyboard over the years, new and used.
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Last edited by indianajo; 6th June 2011 at 10:49 PM.
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Old 7th June 2011, 12:05 PM   #3
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Round plug connections:

Key
Heater (6.3V)
NC
+150V
Audio
Earth
-130V
Heater (6.3V)

There are assorted variants of the diagrams to be found on the web.
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Old 7th June 2011, 06:50 PM   #4
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I think it's keyed by having two fat pins out of the six. Don't have it in front of me to check though. In the interest of safety I'm going to find some one local with the right equipment to test everything and help me power it up the first time. Anyone in Oakland want to earn a few bucks?
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Old 7th June 2011, 11:34 PM   #5
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Diagram for Gibson Clavioline amp, with 6 pin plug shown:
Tube Amp Schematic: Gibson Clavioline

The one I outlined above was for the Selmer variant.
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Old 8th June 2011, 04:26 AM   #6
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I hate to assume it's the same, but... all the Claviolines were made under license so... probably the same or similar enough. Here's where the pins go. Looking at 6J7 specification, I don't know which is heater.
Attached Images
File Type: png Screen shot 2011-06-07 at 9.18.34 PM.png (107.4 KB, 64 views)
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Old 25th June 2012, 02:02 PM   #7
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You could say that I have an interest in Claviolines as I have 7 at the moment. Some will be for sale soon. With regards to what perfectdefect said about no amp, I have just purchased one of the last models which came with a modual that enables you to plug this into the mains, connect the clavioline and use a jack lead to play through a standard amplifier system. I have a photo of this on the CLAVIOLINE PAGE on my web site. I also managed to obtain an original Dealers Service Manual but I do have some service manuals which have been reprinted. Full details on www.chestnutbankproductions.co.uk
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