[pups] PDP-11 / vacuum tube interface

[cube1@charter.net (Jay Jaeger)]

Back in the 1970's Paul Pierce used a D/A converter on a PDP-11 at the UW 
Computer Systems Lab to generate music much like early PC sound cards did 
-- by combining harmonics in various ratios.  Although he happened to have 
used RT-11, there is no reason why it could not be done under Unix.  (The 
UW Computer Systems Lab also had a Votrax).

So, sure, you could, with an A/D and D/A converter do something like 
that.  I am not sure that the various emulators have done emulation for A/D 
or D/A, but in principle, it ought to be possible.

AC coupling (via a capacitor) of the input or output would remove any 
concerns about the relatively high DC voltages.  Besides, input signals 
ordinarily come into the grids of vacuum tube circuits by way of a 
transformer.  Ditto for outputs from tube circuits.

Jay Jaeger


At 05:37 PM 12/9/2008 -0800, Carl Lowenstein wrote:
>On Tue, Dec 9, 2008 at 4:00 PM, Ross Tucker <rjtucke at gmail.com> wrote:
> > Dear all,
> > (This has got to be the strangest cross-post I've ever done.)
> >
> > I have just taken a bet from a friend to challenge my geekiness. I was
> > telling him about my love of Vintage Technology and he proposed that I
> > combine two hitherto separate hobbies and see what happens. The
> > topics: the DEC PDP-11 minicomputer (vintage: 1970s) and vacuum-tube
> > ham radios (vintage: 1960s). I do sincerely apologize for
> > cross-posting, but I am rather younger than either of these
> > technologies (vintage: 1984) and this seems like a monumental
> > challenge.
> >
> > My question for y'all: how could I possibly design+build a project
> > that uses both of these technologies? My thought is to port some radio
> > receiver Digital Signal Processing (DSP) application into PDP-11
> > assembler, compile and run it via emulator on my PC, then use it with
> > the vacuum-tube regenerative receiver that I built a few years ago...
> > Does anybody know if PDP-11 UNIXes even had the capability for a
> > "sound card"?
>
>Well, you could look at "Votrax" on Wikipedia.  Allegedly, the first
>words spoken by a Unix system at Bell Labs, using its Votrax
>synthesizer, were "file not found".
>
>Things that are now known as "sound cards" were called A:D and D:A
>converters back in those days.  And there were a fair variety of them
>available for both Unibus and Qbus systems.
>
> > Or, to get ambitious, I would LOVE to design some
> > interface circuitry between PDP-11 digital circuitry and vacuum-tube
> > electronics... The challenges are legion: the tube side of the circuit
> > operates around 350V DC levels with radio-frequency (RF) signals at 7
> > MHz (almost the clock rate of some PDP-11s!) and I don't have the DEC
> > Handbooks, but I'm pretty sure that even those ancient pre-TTL
> > circuits operate below 350V!
>
>The vacuum-tube circuits may be running from 350 VDC but somewhere
>there are low-level inputs from which everything is amplified.  Think
>microphone.
>
>     carl
>--
>     carl lowenstein         marine physical lab     u.c. san diego
>                                                  clowenstein at ucsd.edu
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---	
Jay R. Jaeger					The Computer Collection
cube1 at charter.net