Vacuum tube oscillator

sizone · Posted: Thu Sep 10, 2009 10:39 am Post subject: Vacuum tube oscillator

Dissatisfied with merely burning out CMOS chips and burning myself on hot power regulators I have decide to increase the voltage and component size on my breadboard.
Working on making a tube oscillator right now, still very much in the early stages, but will be posting samples, design notes and photos here.

tubeosc1.mp3

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tubeosc2.mp3

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andrewF · Posted: Thu Sep 10, 2009 6:21 pm Post subject:

sounds good
is it neon, thyratron or MV type?
keep one hand in your pocket when testing
why post this in circuit-bending?

also, not much talk but plenty of files to peruse
tubesynthdiy

sizone · Posted: Thu Sep 10, 2009 8:29 pm Post subject:

It's posted in circuit bending section because it had to go somewhere in the DIY forum and circuit bending seemed most appropriate for two interconnected reasons. Tube's a 6cm7, medium mu dual triode. Following in the grand metasonix tradition it's a t.v. deflection tube and was not ever designed or intended for audio use. So circuit bent reason 1: it's a misappropriation of technology. Reason 2: it just -sounds- circuit bent and will sound more so once I'm done with it, probably mostly as a result of being based around a kind of wonky t.v. tube.
Circuit's a basic 3 RC phase shift oscillator, only "improvements" I've done so far are a pair of higher value capacitors wired in parallel with with the basic RC network which beef up the tone a little and seem to smooth out the warm up time. Also a roughly 1 meg photoresistor in parallel with the anode bias resistor which does some amplification/distortion (you can hear it in the first sample). Next up is to wire up the other triode and do some cross modulation, also thinking of trying to figure out how to get some more control over the phase (make some vaguely cz-1 type sounds with it and possibly some primitive frequency modulation once both triodes are oscillating). Most of the "work" I've done on it over the past few days has just been going to the electronic surplus store and increasing my supply of higher voltage caps, higher wattage resistors and bigger pots. I think I need to start really figuring out inductors work....
Thanks for the link, more info is always good.
B+ is a modest 130 or so volts DC, one-hand rule is good, but it's not life threatening and I switch the power off before screwing with it. Did learn the hard way that a .1 uf 600v capacitor will hold an unpleasantly high charge and have been more cautious since then about using insulated pliers and being meticulous about discharging.
Could you disambiguate MV for me? Only reference I can think of is millivolt or megavolt. Pretty sure it's not a neon filled type, might be a thyratron but I don't think so. Excuse the ignorance, this is still mostly virgin territory for me.

andrewF · Posted: Thu Sep 10, 2009 9:13 pm Post subject:

no worries, i'm with you on the noise aspect of tube circuits - just the cct-bending forum tends to slip under the radar.

MV = multivibrator, simple oscillator using a dual triode.

gas-filled tubes, like neons and thyratrons are quite different to regular triodes and pentodes, usually they are marked with a solid dot on the schematic.

Yep, caps can take a while to discharge, one PSU I built, still held 100V in the caps after 20 minutes, a resistor across the decoupling caps helps drain them more quickly, I think mine has 3k 10W (??).....been a while since i looked in there.

Navy PreferredCcts1955_MV.jpg

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sizone · Posted: Thu Sep 10, 2009 10:30 pm Post subject:

MV = multivibrator
doh

apropos, not a multivibrator but probably will be some bastard, mutant offspring of one in the near future.
Being under the radar is fine for now. Once it's finished and I can bilk the general populace for lots of money for finished units, that is the time for a high profile.

marmora · Joined: Sep 06, 2009 Posts: 8 Location: Chicago

Wow, I just bought a box of tubes and there's a few 6CM7s in there.
Thanks for sharing, I look forward to seeing where this goes!

sizone · Posted: Sat Nov 28, 2009 9:47 am Post subject:

Thus far: Phase shift osc. WILL NOT WORK using a 6cm7. It's amplification factor is too low.
I've gotten an Armstrong oscillator to work with it. Problem there is that the only way I could control the frequency was by changing capacitors. Also, it was a matter of a lot of trial and error to find inductors that would work (scavenged from power supplies and monitors). Cool thing is that you can set up two l/c oscillators using one tube. By putting both the inductors close to each other I got some interesting fm noises. It's also possible to do strange things by passing a magnet over the inductor.
So I finally broke down and tried a multivibrator, mostly because I've been building them using transistors also scavenged from power supplies and monitors. Works pretty o.k., have it set up just as a fixed frequency osc. right now.
Only two comments.
1: Terminal strips suck.
2: For some stupid reason, with both oscillator designs, I need to "jump start" the thing to get it going by really briefly shorting the grid to ground.
I hope girls find vacuum tubes to be really sexy and this somehow increases my chances at reproductive success because it's been a lot of hassle for very little reward thus far.

tubemultivib.jpg

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Terminal strips are the prototyping method of the damned.

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6cm7multivibe.mp3

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armstrong1.mp3

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