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Old 28th Jul 2019, 8:05 pm   #1
boombox
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Default Wall phone - nothing but trouble, really!

We have an old 746 type wallphone I got on eBay. To be honest it has not been a good buy as it was in poor cosmetic condition, the earpiece speaker has needed to be replaced, the rotary dial has had to be disassembled in order for the dial to return properly, however following faults remain

- Speech is sometimes* very faint for the other party (i.e. on the other end of the line to the wallphone)
- The ringing gongs are hesitant - it's quite a faltering ring.

I've seem the fault finding on BritishTelephones but these instructions are clearly written with someone a bit more familiar with these devices than I am. Are there any clearer instructions anywhere? I had a look on YouTube but there aren't really any clear videos for these phones and these problems.

Thanks all!

* I say sometimes because I'm sure sometimes it's a perfectly normal volume...
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Old 28th Jul 2019, 8:43 pm   #2
Nuvistor
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Default Re: Wall phone - nothing but trouble, really!

It appears to use a carbon granule transmitter, microphone, the carbon granules sometime stick together with moisture from the speech, a sharp tap on the handset used to clear the low volume.

There is probably a much more technical answer.
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Old 28th Jul 2019, 10:22 pm   #3
Dave Moll
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Default Re: Wall phone - nothing but trouble, really!

Certainly, sticky carbon granules in transmitter insets account for a lot of problems. If they don't respond to the "sharp rap" technique, the solution is probably to replace the inset. An electronic "transmitter inset 21A" is the most reliable solution as it does away with carbon granules altogether, and is designed as a direct replacement on 7xx series 'phones.
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Old 29th Jul 2019, 12:06 am   #4
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Default Re: Wall phone - nothing but trouble, really!

Our friend "ThePillenwerfer" has designed a simple transmitter substitute
https://www.vintage-radio.net/forum/...d.php?t=137437
It's on my to-do list of projects.

You may or may not be aware, that if you slacken off the big screws securing the gongs, you will find that by rotating them you can move their distance from the clapper because the "centre" holes are in fact eccentric
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Old 29th Jul 2019, 1:22 am   #5
ThePillenwerfer
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Default Re: Wall phone - nothing but trouble, really!

I've made several transmitters to the design mentioned by Rambo and never had a problem. They've also gone into telephones that I've subsequently sold and I haven't had any complaints.

HOWEVER, early this year I moved my internet and PSTN service from Virgin to PlusNet and found that they didn't work until I upped the zeners in the bridge to 15V.

As for Boombox's bell, the official adjustment instructions are attached.
Attached Files
File Type: pdf Bell No 59A Adjustment.pdf (48.0 KB, 37 views)
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