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uk.tech.digital-tv (Digital TV - General) (uk.tech.digital-tv) Discussion of all matters technical in origin related to the reception of digital television transmissions, be they via satellite, terrestrial or cable. Advertising is forbidden, with no exceptions.

TV socket charge up



 
 
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  #51  
Old April 2nd 17, 08:27 PM posted to uk.tech.digital-tv
Benderthe.evilrobot
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Posts: 148
Default TV socket charge up


"Bill Wright" wrote in message
news
On 02/04/2017 18:46, Benderthe.evilrobot wrote:

Early TVs were AC only - the mains transformer was the only way to get
EHT until they perfected the flyback system.


What about vibrators?


Maybe - if you can get any RF reception whatsoever over the electrical
noise.

6 or 12V vibrators are bad enough - you'd need an awfully big dropper
resistor, or design it for mains primary side voltage and wipe out all
reception in a few mile radius.


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  #52  
Old April 3rd 17, 12:21 AM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Posts: 1,908
Default TV socket charge up

On 02/04/2017 21:27, Benderthe.evilrobot wrote:

"Bill Wright" wrote in message
news
On 02/04/2017 18:46, Benderthe.evilrobot wrote:

Early TVs were AC only - the mains transformer was the only way to get
EHT until they perfected the flyback system.


What about vibrators?


Maybe - if you can get any RF reception whatsoever over the electrical
noise.

6 or 12V vibrators are bad enough - you'd need an awfully big dropper
resistor, or design it for mains primary side voltage and wipe out all
reception in a few mile radius.

---
This email has been checked for viruses by AVG.
http://www.avg.com


Strange then how much portable radio equipment used vibrators in WWII
and Korea.

Bill
  #53  
Old April 3rd 17, 07:05 AM posted to uk.tech.digital-tv
Indy Jess John
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Posts: 1,202
Default TV socket charge up

On 03/04/2017 01:21, Bill Wright wrote:
On 02/04/2017 21:27, Benderthe.evilrobot wrote:

6 or 12V vibrators are bad enough - you'd need an awfully big dropper
resistor, or design it for mains primary side voltage and wipe out all
reception in a few mile radius.


Strange then how much portable radio equipment used vibrators in WWII
and Korea.

My 1957 Rover had a valve radio powered by a vibrator to generate the HT
voltage. There was no interference from the power supply which sat just
behind the radio.

Jim

  #54  
Old April 3rd 17, 07:53 AM posted to uk.tech.digital-tv
Ian Jackson[_7_]
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Posts: 66
Default TV socket charge up

In message , Bill Wright
writes
On 02/04/2017 21:27, Benderthe.evilrobot wrote:

"Bill Wright" wrote in message
news
On 02/04/2017 18:46, Benderthe.evilrobot wrote:

Early TVs were AC only - the mains transformer was the only way to get
EHT until they perfected the flyback system.

What about vibrators?


Maybe - if you can get any RF reception whatsoever over the electrical
noise.

6 or 12V vibrators are bad enough - you'd need an awfully big dropper
resistor, or design it for mains primary side voltage and wipe out all
reception in a few mile radius.

---
This email has been checked for viruses by AVG.
http://www.avg.com


Strange then how much portable radio equipment used vibrators in WWII
and Korea.

Indeed.

Much of the military equipment had a DC HT line, and an external (and
occasionally internal) power unit was required to provide the high
voltage when operating from a 6 or 12V battery. This would either be a
motor-dynamo (a 'dynamotor') or a 'vibrator pack'.

There were two forms of vibrator pack - 'synchronous' (where the AC
output from the secondary of the step-up transformer was rectified by a
pair of contacts which operated in synchronism with the contacts that
chopped the DC feed to the primary) or 'non-synchronous' where the HT
rectification was carried out by a rectifier valve.

Neither form of power supply was noted for creating electrical noise
that could not be adequately eliminated by the usual built-in RF
filtering.

I've never had any experience with dynamotors, but for my first mobile
amateur radio transmitter (which home made), in my old 1953 Ford
Prefect, I used a 6V synchronous vibrator pack intended for a
Hallicrafters receiver. The receiver, an army R109, had its own internal
vibrator. I still have an army R107 receiver - and it has both an
internal conventional mains power supply and a 12V vibrator supply. The
latter has only ever been used once in earnest.
--
Ian
  #57  
Old April 3rd 17, 06:53 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
external usenet poster
 
Posts: 1,908
Default TV socket charge up

On 03/04/2017 08:05, Indy Jess John wrote:
On 03/04/2017 01:21, Bill Wright wrote:
On 02/04/2017 21:27, Benderthe.evilrobot wrote:

6 or 12V vibrators are bad enough - you'd need an awfully big dropper
resistor, or design it for mains primary side voltage and wipe out all
reception in a few mile radius.


Strange then how much portable radio equipment used vibrators in WWII
and Korea.

My 1957 Rover had a valve radio powered by a vibrator to generate the HT
voltage. There was no interference from the power supply which sat just
behind the radio.

Jim

I had a valved Radiomobile which was the same.

Bill
  #58  
Old April 3rd 17, 06:54 PM posted to uk.tech.digital-tv
Graham.[_12_]
external usenet poster
 
Posts: 404
Default TV socket charge up

On Fri, 31 Mar 2017 14:01:05 +0100, Bill Wright
wrote:

On 31/03/2017 09:51, NY wrote:


Were old live chassis TVs full-current half-mains or did they have hefty
current-limiting resistors? Was there a risk of the aerial being at
half-mains when it was plugged in? I realise that all other exposed
parts of the chassis (eg volume and channel changing knobs on front)
were big bakelite things which would have provided plenty of insulation.


The isolating caps were usually built into the socket. If the socket got
broke some repair men would fit a stock one that didn't isolate, or they
might solder a bit of coax to the tuner input and run it to the outside
of the set.

My dad taught me to test every aerial with a dry finger end before
grasping it.

The old valve radios were terrible for this. I don't know what the
voltage or current was but it certainly hurt. It would send you flying.

Bill


You will recall that 1949 vintage Cossor 916 that I restored a few
months ago, that has got a paxolin board that caries the B-L aerial
socket, and I would have expected a couple of isolating capacitors on
there too, but no. There is a 1000pF from the outer of the socket to
chassis, and a 1M ohm static discharge resistor again from the outer
of the socket to mains neutral, before the DP switch.

There are two isolating caps, but they are in the RF/IF strip.
There is nothing obvious about these two 1000pF caps that would
suggest their vital importance to the uninitiated.

A long coax cable runs from the socket to neat the front of the set to
where the input of the RF/IF unit is and this cable is supported by
several metal terry clips bolted to the chassis, so you hope that the
outer sheath is undamaged at these points.


--

Graham.
%Profound_observation%
  #59  
Old April 3rd 17, 09:03 PM posted to uk.tech.digital-tv
Benderthe.evilrobot
external usenet poster
 
Posts: 148
Default TV socket charge up


"Bill Wright" wrote in message
news
On 02/04/2017 21:27, Benderthe.evilrobot wrote:

"Bill Wright" wrote in message
news
On 02/04/2017 18:46, Benderthe.evilrobot wrote:

Early TVs were AC only - the mains transformer was the only way to get
EHT until they perfected the flyback system.

What about vibrators?


Maybe - if you can get any RF reception whatsoever over the electrical
noise.

6 or 12V vibrators are bad enough - you'd need an awfully big dropper
resistor, or design it for mains primary side voltage and wipe out all
reception in a few mile radius.

---
This email has been checked for viruses by AVG.
http://www.avg.com


Strange then how much portable radio equipment used vibrators in WWII and
Korea.


Yes; off batteries - where RFI is easier to control.


---
This email has been checked for viruses by AVG.
http://www.avg.com

  #60  
Old April 3rd 17, 09:19 PM posted to uk.tech.digital-tv
Ian Jackson[_7_]
external usenet poster
 
Posts: 66
Default TV socket charge up

In message , Benderthe.evilrobot
writes

"Bill Wright" wrote in message
news
On 02/04/2017 21:27, Benderthe.evilrobot wrote:

"Bill Wright" wrote in message
news On 02/04/2017 18:46, Benderthe.evilrobot wrote:

Early TVs were AC only - the mains transformer was the only way to get
EHT until they perfected the flyback system.

What about vibrators?

Maybe - if you can get any RF reception whatsoever over the electrical
noise.

6 or 12V vibrators are bad enough - you'd need an awfully big dropper
resistor, or design it for mains primary side voltage and wipe out all
reception in a few mile radius.

---
This email has been checked for viruses by AVG.
http://www.avg.com


Strange then how much portable radio equipment used vibrators in WWII
and Korea.


Yes; off batteries - where RFI is easier to control.

When are vibrator power supplies powered 'not by batteries', and in what
application?


--
Ian
 




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