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Vintage Telephony and Telecomms Vintage Telephones, Telephony and Telecomms Equipment |
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27th Apr 2017, 8:24 pm | #1 |
Pentode
Join Date: Aug 2016
Location: Dunstable, Bedfordshire, UK.
Posts: 140
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Mic won't work on Tele 310
As above, I just can't get the mic to work. Have tried the handset on a different phone and it works fine so it can't be that. I've traced out all the connections on the phone and get continuity on everything. I also get a dial tone. I've bridged out the dial between D4 and D5. A visual inspection shows the wiring to be in good condition. The only odd measurement was around 50 ohms on the induction coil between 3 and 4.
I'm guessing I might have to solder in a new induction coil but I just wanted to make sure I wasn't missing anything obvious. On the diagram (N410) I've connected my phone cords to T1 and T8 and bridged T1 and T2. I've got my own PBX. Any ideas? |
27th Apr 2017, 9:19 pm | #2 |
Octode
Join Date: Mar 2011
Location: Sheffield, South Yorkshire, UK.
Posts: 1,453
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Re: Mic won't work on Tele 310
To be honest I can't make much sense of N410. However, similar instruments have the 75Ω part of the coil in parallel with the receiver and 30Ω non-inductive resistance which would lower the resistance reading between coil terminals 3 and 4 if these weren't disconnected first.
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27th Apr 2017, 9:30 pm | #3 |
Pentode
Join Date: Aug 2016
Location: Dunstable, Bedfordshire, UK.
Posts: 140
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Re: Mic won't work on Tele 310
Ok thanks.
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29th Apr 2017, 3:27 pm | #4 |
Pentode
Join Date: Aug 2016
Location: Dunstable, Bedfordshire, UK.
Posts: 140
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Re: Mic won't work on Tele 310
Traced it to a short on the 0.1uF cap. thus shorting out the speech network. Odd as it's not often these fail. Does anyone have a spare square one?
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29th Apr 2017, 4:03 pm | #5 |
Octode
Join Date: Mar 2011
Location: Sheffield, South Yorkshire, UK.
Posts: 1,453
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Re: Mic won't work on Tele 310
Thanks for the up-date; I'd been wondering about it.
I doubt it would matter if you left that cap disconnected. You could also replace it with a normal modern one, but it's a different matter if you want to keep things original. Another option would be re-stuffing as there'd be plenty of room. |
29th Apr 2017, 4:42 pm | #6 |
Dekatron
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 3,687
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Re: Mic won't work on Tele 310
All that cap is for is to bypass any RF if you're located near a transmitter and the carbon mic decides to act as a demodulator.
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Regds, Russell W. B. G4YLI. |
29th Apr 2017, 9:36 pm | #7 |
Pentode
Join Date: Aug 2016
Location: Dunstable, Bedfordshire, UK.
Posts: 140
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Re: Mic won't work on Tele 310
Well the most interesting part was finding the fault. I've got a few spare GPO caps around, prob. will fit one then shove it in the attic tbh.
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