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Joined: May 2018
Posts: 4
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I have a GTE Automatic Electric Model 186 6-button keyset phone and Precision Components 4A speakerphone (108A loudspeaker and 608A transmitter plus a spare 608A) that were used by my supervisor at the time they were taken out of service a few decades ago. I have all the components including the 82A connecting block and a cord to go from the connecting block to an RJ11 jack. I can get dialtone in the handset or the speaker and can receive a call on either, but when I push the dial buttons I hear tones but the CO does not respond. It's possible that I'm getting single tones instead of dual tones, which I judge by comparing to the tones of a working SC2500, but my hearing discrimination may not good enough to tell for sure.
Two questions:
1) Does my hypothesis about the tones sound plausible? Any suggestions for checking this with a 'scope would be welcome. Is there a schematic for the Model 186 phone available anywhere?
2) Does this collection of equipment have enough value to warrant trying to diagnose the problem? I don't really have a strong desire to use the phone myself, but I'd like to clear it out of my storage and I'd rather not have it go to the landfill. Selling it would be a bonus. I see a 4A speakerphone on ebay and it does not even include the connecting block.
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Joined: Dec 2007
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Joined: May 2018
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Thank you for that pointer.
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Joined: May 2018
Posts: 4
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Using the schematic to hook up my 'scope I verified that the dial buttons were producing dual tones, not just one. Then using a spectrum analyzer app on my iPhone I discovered that the column frequencies were about 3.5% low, which is sufficiently out of spec to be ignored. The oscillator in this Touch Calling unit was built with inductors having a tunable ferrite core so I was able to adjust the frequencies within 0.5% of spec and now all the digits are signaled correctly. Thanks for your help.
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Joined: Dec 2007
Posts: 6,819 Likes: 21
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Retired Admin
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Dial tone is two tones DTMF or Dual-Tone Multi-Frequency The correct frequencies can be found here: DTMF
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Joined: May 2018
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