Challenge: Complete the circuit

[markosjal]

To see if anyone can....

This is taken from an old "Answer only" phone that was built into an AE style handset and Sold in Fred Meyer Stores in the Portland area in the 1970s . I had copied this circuit before, putting it in a WE handset and added a Buscom soft touch for DTMF generation. I remember that I literally had to break the AE type handset open to see the circuit as it seemed all glued together. Was too young and stupid to try a strap (oil filter type) wrench. I was always impressed with this because it seemed to work pretty well although did have some (squeal) feedback with the buscom Soft Touch dialer. I later used this in some WE 202s.

Complete the circuit:

AE or WE receiver with diac
AE or WE Carbon Mic
1 MF capacitor
DIAC (removed from a different receiver element)
330 (?) ohm resistor
220 (?) ohm resistor

2 Diacs total.

The components were soldered into a simple square and as I recall. Each component a side of the square.  The two resistors were soldered at a common point The diac and capacitor at another common point then the diac+Cap and res+res soldered together to form a square.

interested in knowing what someone may come up with!

[Jack Ryan]

To tell the truth, I don't know what the question is but I was wondering what a DIAC was doing in a receiver circuit.

Thanks

Jack

[dsk]

The symbol of the diac is equal to the symbol of 2 diodes bridged in opposite direction. The diodes was commonly used to suppress loud clicks in the receiver, just because it shorted out the receiver at 0.7V   I do actually not know how a diac is working, but probably the same way with a higher voltage.

dsk


PS If so in series with a ringer it should be an effective anti tinkle device... ?? DS

[Jack Ryan]

The symbol of the diac is equal to the symbol of 2 diodes bridged in opposite direction. The diodes was commonly used to suppress loud clicks in the receiver, just because it shorted out the receiver at 0.7V   I do actually not know how a diac is working, but probably the same way with a higher voltage.

dsk

PS If so in series with a ringer it should be an effective anti tinkle device... ?? DS

A diac is a bit like an SCR in that once it fires, the current has to drop to zero to reset it. It is not the right device for transient protection in this application and is not the same as two diodes back-to-back.

What's needed is a pair of back-to-back (perhaps Schottky) diodes or similar. At least in my humble opinion.

Jack

[dsk]

About the anti tinkle, look at this page: http://www.epanorama.net/circuits/tele_privacy.html
dsk

[Jack Ryan]

I think I should have stayed out of it. I thought the subject was receiver surge suppression.

There are a lot of approaches to anti-tinkle. A lot of the electronic approaches cause a delay and interfere with some auto line test systems.

A bias spring works, a thermistor works and often a simple resistor works.

Jack