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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
Tube VCA question/idea--low voltage plate triodes?
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cslammy



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PostPosted: Sat Jul 18, 2020 8:05 am    Post subject: Tube VCA question/idea--low voltage plate triodes?
Subject description: Anyone know if this exists
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On the bench I have been messing with the 1J24B pentode that Ken uses in his tube VCA

Very intersting part, you can still get 'em pretty cheap, low plate and heater voltages and currents throughout, making it good for stomp boxes, battery powered effects, etc., good when you don't want to burn down your house. Razz

My thought: can 4x of these be used for a tube op amp. Has anyone tried this? that could lead to all sorts of useful things right?

Better yet would be if there is a low plate voltage/low heater version that's a dual triode, so a 2V heater version of the 12AX7 for instance.

So far I've never seen anything like it, closest I have found is 6N17B but that's 6V heater and maybe 75V plate....way higher vs. 1j24.

Ideas? Links? This must not be easy or everyone would be doing this right?

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JovianPyx



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PostPosted: Sat Jul 18, 2020 9:06 am    Post subject: Reply with quote  Mark this post and the followings unread

One of my first electronics jobs was at MSA (Mine Safety Appliances). One of the many things they sold were electronic gas analyzers for various purposes. I serviced these devices. One of these was called a LIRA for Luft Infra Red Analyzer. These devices used a differential tube amplifier wired as an operational amplifier made of 12AX7 tubes. This was a precision device, so it would seem that you should be able to get something out of a musical application.

Lowest plate voltage is a spec you'll have to search for.

A tube that is operated at a less than optimal plate voltage is called a "starved plate" application and results in distortion. PAiA makes a device like this (I forget the name).

I played with tubes a lot as a kid because there were no transistors, I didn't have a high voltage power supply (what a HAM would call "high voltage"). I used line voltage (120VAC) into a fullwave (yeah, I know, not a great idea) with caps to get a PSU that put out 165 VDC or so which seemed sufficient for any of my projects.

There ought to be some information about a vacuum tube operational amplifier on the web. I do remember from the MSA LIRA schematics - lots of resistors. Be prepared to use higher wattage resistors than with silicon opamps or CMOS Cool

I will be interested to read about your progress in this, reminds me of "the good old days".

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