[sdiy] Tube amplifier question

[Scott Stites]

Ken Stone wrote:

> Well... I had a Hohnerola, and that is rarer - you will find only one
> mentioned on the web besides mine, and that was in the siemens lab. I
gutted
> it to build my current synth into!
>
> Sometimes a classic is beyond help, so recycling it is fine.

That's heartening news - it really is in great shape, and having two
keyboards and a foot controller all in a fairly attractive chassis will be
nice.  And the keyboards/footpedals are constructed really well - it looks
like they'll last a lifetime.

===
Roy J. Tellason wrote:

> Only 13?  Some of those tube models had quite a few more than that.  The
ones
> that really got me were the oddball ones,  like "three-plate tetrode"
tubes
> that some of the old Lowrey tube stuff used.  Combining that with
"packaged
> circuits" I never did quite understand how those worked,  though watching
the
> neon bulbs used for keyers was kind of nifty and did help you find things.
>
> What tubes were used in the unit you got?

12AX7 (three of them)
12AU7 (eight of them)
EZ81/C6A4 (one of them)
6V6 (one of them)

> You guys have any comments on these as a starting point?

The keyboard that I've been using for the past couple of years is based
around this really cheap (and I do mean *cheap*) little put-together
keyboard that I bought from some supplier on the web.  It's a membrane
contact type of thing, with really tiny little keys.  I took the circuit
board, desoldered all of the parts off of it, cut up the traces with an
exacto blade and soldered in a matrix with bus wire.  I  put a digital
keyboard design from Thomas Henry's "Build a Better Music Synthesizer" on
protoboard and wired the keyboard into that.  It is quite a useful design -
it has a three position switch for setting octaves, a modulation input
(which is exceedingly handy for vibrato), and an exponential glide (though I
prefer linear glide for the most part).  I believe the same circuit is in a
copy of Electronotes that he wrote as well.

By chance, the other day, I found a PDF on my hard drive named
'friendly.pdf' written, IIRC, by John Simonton.  It has a section in it that
is pretty much the same encoder circuitry that Thomas used.  The ADC part
isn't in there (John was writing this in support of some early computer
stuff, and the circuit fed into there), but the ADC part wouldn't be too
hard to rig up.  I can't copy the TH book, but the I can send the
above-mentioned PDF to you, (contact me off-line if interested).

Then, of course, Ray Wilson has a resistor divider design at his Music From
Outer Space site.  And there are also some Oberheim circuits out there (2V,
4V) that look pretty nice, actually.

===
Mike B. wrote:

> An Estey organ??  It's only heresy if you don't use chainsaw during the
> disassembly.

So, I gather I won't be missing much? =-D

Cheers,
Scott