[pups] PDP-11 / vacuum tube interface

Carl Lowenstein carl.lowenstein at gmail.com
Wed Dec 10 11:37:31 AEST 2008

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

    carl lowenstein         marine physical lab     u.c. san diego
                                                 clowenstein at ucsd.edu

More information about the TUHS mailing list