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Other Vintage Household Electrical or Electromechanical Items For discussions about other vintage (over 25 years old) electrical and electromechanical household items. See the sticky thread for details.

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Old 19th Sep 2020, 2:12 pm   #1
Gridiron
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Default What was this Mains Isolator unit used for?

I found this box amongst various junk when looking for a short length of mains cable. As wired it appears to short the mains in the ON position! A DIN speaker socket, switch, transformer and 82 ohm resistor on/in the box.
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Old 19th Sep 2020, 2:16 pm   #2
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Default Re: What was this Mains Isolator unit used for?

It says mains, but it's a headphone/speaker accessory for a non-isolated TV set.
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Old 19th Sep 2020, 2:27 pm   #3
Gridiron
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Default Re: What was this Mains Isolator unit used for?

Presumably mains cable (if original) was used as a convenient 3 way cable. How was it connected to the set, was it permanently wired or was there a plug/socket arrangement?
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Old 19th Sep 2020, 2:42 pm   #4
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Default Re: What was this Mains Isolator unit used for?

Not a consumer fit I'd have thought. I've seen it advertised somewhere, it stirred a memory!
Edit: It may have been one of those disposal places in PTV or PW?
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Old 19th Sep 2020, 9:39 pm   #5
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Default Re: What was this Mains Isolator unit used for?

Quote:
Originally Posted by Gridiron View Post
....How was it connected to the set, was it permanently wired or was there a plug/socket arrangement?...
This unit would have been permanently wired to the set by a technician, often with the speaker isolating unit (to give it a more correct name) fitted to the rear of the television set with a couple of screws through the back.
The switch is wired in series with the "hot" side of the television sound output stage and internal speaker positive the connection to allow the internal television speaker to be muted, the third lead being common ground/speaker negative.

The isolating transformer then allows an external speaker or tape recorder/amplifier to be safely connected.

I only ever seem to recall seeing one of these units in use back in my "rental' television repair days on either a BRC 3500 or a TX9 chassis, I can't remember which.....

Andrew
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Old 19th Sep 2020, 9:56 pm   #6
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Default Re: What was this Mains Isolator unit used for?

Quote:
Originally Posted by Gridiron View Post
Presumably mains cable (if original) was used as a convenient 3 way cable. How was it connected to the set, was it permanently wired or was there a plug/socket arrangement?
That would have been a Radio Rentals item, I fitted a fair few of the near identical Granada TV Rental ones. I think we simply snipped the wires room the speaker and grafted on the three core cable with a chock-block inside the set the cable was routed through a ventilation slot in the back cover.

There was a second box that had a volume control and a 3.5mm jack for the supplied earpiece. The two boxes were connected with a long cable with 2 pin DIN plugs at each end.
They were a consession made for our hard-of-hearing subscribers rather than anything else, I think we fitted them FOC
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Old 19th Sep 2020, 10:02 pm   #7
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Default Re: What was this Mains Isolator unit used for?

I made my own for recording from a Sobell TV to my Grundig tape recorder.

I would have been around 14 and it was built into a 2 part Blue and orange slide case with a DYMO title (done at school) Tip of the Pip Toy.

I may even still have it although little from this period survives having been dumped by my parents whilst I was in Portsmouth.

Yes I used it to record Top of the Pops.

The speaker on this set was not isolated by the output transformer.

I do still have the tape recorder and some of those recordings.

Cheers

Mike T
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Old 26th Sep 2020, 6:19 pm   #8
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Default Re: What was this Mains Isolator unit used for?

Looks familiar, fitted by DER or RR to Subscribers who had hearing problems, so they could use Head phones or Earpiece, also we fitted something similar for the Hearing Aid Inductive Loop Systems, I recall.
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Old 28th Sep 2020, 8:19 am   #9
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Default Re: What was this Mains Isolator unit used for?

A lot of these were used to connect an hearing aid when I was at Granada/DER Ltd.
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