Re: [pups] PDP-11 / vacuum tube interface - TUHS

10 Dec 2008

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
&lt;rjtucke(a)gmail.com&gt; 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(a)ucsd.edu
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Jay R. Jaeger					The Computer Collection
cube1(a)charter.net