Tube Challenge!!

Harry Bissell harrybissell at
Mon Nov 29 07:39:23 CET 1999

"High impedance tube" is not an oxymoron (see jumbo shrimp, military
High impedance tube is "redundant".

Also: most oscillators are really "current controlled oscillators"

And: You are all still crazy !!!  (this is fun, not flame...)

:^) Harry (How many DIYers doesa it take to change a thyratron ???) Bissell

media at wrote:

> At 1:39 PM -0700 11/24/99, Doug Tymofichuk wrote:
> >
> >> Tube VCA's seem easy enough, but I think building a tube
> >> ADSR to control that VCA would be next to impossible.
> >
> >Why? ADSRs are mostly just switching and charging
> >capacitors. I would think that the ADSR would be an easier
> >module to design, just using thyratrons.
> Most of the ADSR circuits I've seen use op-amps and NAND gates.  I'm sure
> it would take quite a few tubes to replace a 4001.  By "next to impossible"
> I meant that it might be possible, but probably wouldn't be worth it.  If
> you know of an easy way using thyratrons I'd like to hear it.  I'm gussing
> it involves some sort of "thyratron gate."  Eliminating op-amps from the
> design would simplify the power supply (ie. no need for +15/-15).
> >But I think that I could live with a solid state ADSR running a tube VCA. And
> >tube VCAs are VERY easy to build.
> I think I could live with that too, as I can't think of any audio advantage
> of having an all tube ADSR, besides the "Tube Challenge!!" aspect.
> >> Sample and hold is another matter
> >> entirely! How about a tube noise source??
> >
> >That could be fun, you could use a tube geiger counter to
> >generate random noise.
> What's a geiger counter??  I thought it was a device used to measure
> background radiation.  I have no idea how they work.  Getting parts is
> difficult enough without searching for plutonium on the black market :)
> >Sample and hold ought to be fairly easy with high-impedance tubes.
> I thought "high-impedance tube" was an oxymoron.
> >If you could
> >> build tube VCO's, VCA's, VCF's, ADSR's, and LFO's, how
> >> would you mix modulation sources??  For example, how would
> >> you send a mix of LFO and keyboard voltage to control the
> >> VCF??  What's the best way to sum voltages using tubes??
> >
> >What's wrong with doing just like in solid state, with
> >voltage dividers?
> I really don't know.  That's why I asked.
> >Also, keep in mind that tubes with multiple grids can do amazing things
> >with modulation with ease. There are some things that are far easier
> >to do with tubes!
> This is true, but otoh there are types of modulation that are easier in
> solid-state.  Look at Rene Schmidt's neon VCO, it's more of a CCO, a
> current-controlled oscillator.  A typical modular is built around the idea
> of patching control voltages where one output can be sent to many inputs.
> While I'm not saying that this isn't possible using tubes, it will
> introduce new problems involving impedance matching.
> >> So I'm thinking that many of the basic features found in
> >> subtractive synthesizers (eg. ADSR, S&H, keyboard tracking,
> >> modulation mixers) would be impossible, or impractical far
> >> beyond any desire for novelty, to build with tubes.
> >
> >I disagree. In fact, the biggest reason that this has not
> >been done to date, IMHO, is that very few people have made
> >the effort. Thousands and thousands of people have spent
> >decades on solid state synthesis. Only a handful have
> >spent a few years on tube synthesis. If we used one tenth
> >of the time this list has spent on tempcos, for example,
> >on tube design, we ought to be able to come up with some
> >truly great stuff.
> I agree with that.  My point was that an all-tube synth with all the
> features of a common monosynth, like an SH-101, would be the size of a
> small refrigerator and draw just as many amps.
> >Actually, the more that I think about it, the more that I
> >feel that we have a very unique opportunity here. We can
> >spend our time refining and "improving" solid state synth
> >designs, or we can instead spend time designing entirely
> >new circuits, using tubes, going where no one has ever been
> >before. Overall, I feel that tubes are easier to work
> >with and design with, and there are a lot of unexplored
> >areas to check out. And some things may not be practical
> >with tubes, and that's fine, because there are going to be
> >some things that we find tubes will do quite easily, that
> >solid state cannot. That's where the biggest reward for all
> >this comes in, when you come up with something completely
> >new, that has NEVER been done before.
> I totally agree.  I just took a look at the Hellfire at the Metasonix
> website.  It seems to do things that have never been done with solid-state.
> One thing that confuses me is its PWM control.  I've always thought that
> pulse-width modulation was varying the duty cycle of a square wave, but
> this thing doesn't seem to have any sort of oscillator.
> Can you think of any historical applications where tubes were used for
> voltage or current controlled resonant filters??
> P.S.  Here are some tube sites someone sent me:
> - audio amplifier design
>  - guitar amplifier design
> amps and Eric Barbour's
> stuff
> - SPICE models
>  - tube "op-amps" and headphone amps
>  - tube basics
>  - tube data sheet locator

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