Telephone 332. Excessive side tone.

[thaistyle]

Split from this thread:-

https://www.vintage-radio.net/forum/...ad.php?t=39536

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I've just seen a reference to side-tone. I have just restored and converted a 332L, installing a 4t receiver and also a 21A transmitter, but I seem to be getting too much 'side-tone' - my voice seems far too loud in the handset receiver. I would be grateful for suggestions on how to reduce this issue.
Thanks,
Jim

[russell_w_b]

Originally Posted by thaistyle

'...I have just restored and converted a 332L, installing a 4t receiver and also a 21A transmitter, but I seem to be getting too much 'side-tone...'

Are you far from the exchange? If not, you may experience lots of side-tone. The receiver you fitted is a 'balanced armature' type (more sensitive) and is probably not matched to the induction coil in your 332. I would revert to the original receiver with slide-off diaphragm (there are two types: 'Inset 11' - non-equalised, and the equalised 'Inset 2P'). The difference is observed by looking at the holes in the bakelite cup: the 'equalised' 2P has a central recess with the holes closely spaced, and - inside - the magnet coils are out-of-sight with just the pole-pieces, mounting screws and small cloth vent showing. The older 'Inset 11' type will reveal bobbins and all when the diaphragm is slid away, and the bakelite ear-cup is purely convex with wider-spaced holes.

The 'equalised' 2P receiver is 10 - 15db more sensitive than the original type. Your balanced armature 4T is probably way too sensitive. I would keep the 21A mic, though!

[dagskarlsen]

You could start with adjusting the current to about 25 mA by putting recistance in series with the microphone element, if thats not enough, you have to put some resistance in parallell with the receiver, try 220 ohms, more if you get to little sound, less if you get to much.
Then test by using it, and ask the other end if they hear you well, and test what you hear.

dsk

[thaistyle]

Thank you for that suggestion..I will start with 220 and see how it goes.
Will report back on the results.

[beery]

Hi All,
I would recomend using reciever 2P.
Even with a 21A mic excessive side tone should not be a problem.
I've got phones like this connected to my own strowger system made with main exchange parts (2000 type Non-Director) and you can't get much closer to the exchange than that!.

Things to check...
The hook switch has two sets of contacts. One connects the DC path through the phone. The other contacts connect the AC signal path, check that this contact set is working correctly.
Check how it is wired up.

If you are not using individual ADSL filters:-

The original 2uF cap should be disconnected by removing the link between terminals 10 & 11.
The blue wire from the line cord must go to terminal 11. Otherwise you will have problems with the sound transmission and sidetone will be a problem.

Your 3k3 resistor (added in series with the ringer to reduce the ren value) can either go in place of the link between terminals 11 & 12 or in place of the link between terminals 1 & 2.

If you are using ADSL filters of the separate type then I would re-instate the internal 2uF capacitor and leave the blue wire disconnected.

Mind you though I would never recomend the use of separate ADSL filters. The single overall types give much better bandwith and are not bothered when you dial out on an old phone. You can get these from ADSL Nation.

Another but rare possiblity is an oc winding in the induction coil.

Cheers.
Andy