Re-installing a TouchTone keypad in an ASR-33

Ethan Dicks ethan.dicks at
Wed May 20 17:54:32 CDT 2009

On Wed, May 20, 2009 at 6:23 PM, Brent Hilpert <hilpert at> wrote:
> Ethan Dicks wrote:
>> If it's an ITT or other non-Western Electric phone, I'd wager it's
>> IC-based.  AFAIK, only the W-E phones (i.e., pre-breakup) would have
>> the 1-transistor-2-coil keypad.
> As indicated in my previous message on the topic, Automatic Electric was
> producing a 1-transistor DTMF design in the 60/70's, almost identical to WE's.

I'm unfamiliar with Automatic Electric.  Did they make home phones or

> I don't know what it was like in the Bell/WE regions, but out here DTMF, while
> available, didn't really take off until sometime in the late 70's/80's I would
> say, perhaps in correlation with the switch to IC-based DTMF.

I don't recall when I saw my first TouchTone phone (besides the ones
at COSI, the local science museum, in the Bell exhibit), but probably
not until the late 1980s.

> I'm guessing the
> number of 1-transistor DTMF phones produced was relatively small,
> (particularly) compared to the number of dial phones produced in the same time period.

Compared to dial phones?  A small number, I'm sure.  Compared to
IC-based-TouchTone, also a small number.

I checked... coincidentally enough, the phone in my bedroom is a
Western Electric 1-transistor-DTMF, made around 1981.  It mostly still
works, but frequently, when I pick up, the audio is very soft until I
thwap the side of the phone (not the handset)... I don't use it often
enough to have taken the time to check it out yet.

Back at Pole in 2004, our science tech was also the drummer in the
band that year (and other years, too).  We were playing "Never There"
by Cake and needed a particular TouchTone sound for a percussive
element of the song - the "1" key, ISTR.  I offered to whip up a
556-based fixed-tone generator, but our Drummer tore into an ITT phone
(installed probably when ITT Antarctic Services had the 10-year
services contract in the 1980s), and stuck in a 9V battery and a 1/4"
mono-out jack, giving him a 12-tone instrument to play that just
happened to look like a telephone.  I was surprised he was able to do
that, since my experience tearing apart phones as a kid was the
1-transistor design that I didn't understand at the time, but when I
saw he had an IC-based keypad to work from, how he did it was clear.

I am enjoying exploring the nuances of the 1-transistor design, but
I'm sure I don't fully appreciate how it works yet.  The IC-based DTMF
generators are somewhat obvious to me at least.


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