On 29 December 2015 at 20:15, Chuck Guzis <cclist
at sydex.com> wrote:
It was particularly amusing that in the heart of
Silicon Valley in the
1980s, Pacific Telephone still had many of its exchanges outfitted with
crossbar switches--with your shiny new touch-tone telephone, you could hear
the clicks in the background audio as the gear converted the DTMF to
Those pulses depend on what kind of crossbar you were homing on, and
where you were calling.
On a Number 5 Crossbar, your DTMF was never converted to dial pulse
for the switch itself. The Touch-Tone Register would connect to a
digit translator that inputs the 2-of-5 binary code directly into the
relays of the Originating Register (which can still receive dial
pulse). On Number 1 Crossbar and Panel however your DTMF would be
converted to 20 pulse per second dial pulsing. Only in Step-by-Step is
your DTMF converted down to "normal" 10 pulse per second dial pulsing;
though it should be noted that in step it either gets converted by a
"dumb" Touch-Tone Reciever Converter (DTMF goes in, dial pulse goes
out) in a direct control step, in a common control step (yes that was
a thing) the DTMF actually ends up getting converted in the same way
as on #5XB with the common control elements dial pulsing.
However it should be noted: Crossbar switches make noise when
connecting through the switch fabric; and depending on trunking and
the kind of switch you're calling you might hear dial pulsing, panel
call indicator pulsing, or revertive pulsing. RP would be sent on a
direct connection between a crossbar to a Number 1 Crossbar or Panel
switch (and to Number 5 Crossbar occasionally). PCI is something you'd
*never* hear in the 80s, since the only tandems that required PCI
(namely Panel Sender Tandem) were gone by the 70s, and the tandems
that replaced them (Crossbar Tandem) while it can still "speak" PCI
would be more likely to use MF tones; also end offices that would use
PCI, namely manual offices, were also dead and gone by the 80s. Dial
pulsing however... well that goes to step offices, and if you have a
step tandem anywhere in the chain (you could have a #5XB to #5XB call
which you'd think would be MF'd; but if you have a step tandem you get
In the late 1960's I was what was then called a student apprentice.
This ment you did two weeks at work and one week at college.
I worked at at local cable manufacturing company and my desk was in the
high voltage lab.
The building had been part of the Great Western Railways wartime
It was a concrete blockhouse. Walls three feet thick and blast shutters
over the windows.
It had the advantage of being warm in winter and cool in summer.
We had a high votage test lab (up to 500,000 volts) , RF lab and the
internal telephone exchange.
You could not dial out. There was a manual switch board with its own
operators for that. (dial 0 and ask)
The internal exchange was a standard GPO Strowger type exchange.
It would have been 25-30 years old at that time but built under wartime
One monday I arrived back at work from college to find a box on my desk
containing many reels of PVC hook up wire and a set of tatty wiring
There was a note from my boss saying "insulation in phone exchange
cracking up - please rewire the lot"
First job stick the blueprints on the glass partition between my lab
and the exchange with a light behind them.
Then to the exchange, take all the covers off the relay banks and
sitting on my tall lab stool watch what happened.
Boss goes past and nods his approval and I went from there. Took a
couple of months but it worked when I'd none.
We were right on the London main line.