UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Television Standards Converters, Modulators etc

Notices

Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions.

Reply
 
Thread Tools
Old 19th Nov 2022, 10:12 pm   #1
EnyaFox
Triode
 
Join Date: Mar 2022
Location: Reading, Berkshire, UK.
Posts: 32
Default SPT Video RF Modulator

Hello,

I have obtained a rack mount RF modulator today. I can't seem to find any information about SPT or this modulator. I have included a few photos. If you know anything about it, please let me know!
Attached Thumbnails
Click image for larger version

Name:	IMG_20221119_215657.jpg
Views:	121
Size:	44.4 KB
ID:	268380   Click image for larger version

Name:	IMG_20221119_215720.jpg
Views:	109
Size:	30.1 KB
ID:	268381   Click image for larger version

Name:	IMG_20221119_215706.jpg
Views:	104
Size:	56.8 KB
ID:	268382  
EnyaFox is offline   Reply With Quote
Old 22nd Nov 2022, 2:55 pm   #2
coil1234
Pentode
 
Join Date: Jan 2006
Location: Almeria, Spain
Posts: 212
Default Re: SPT Video RF Modulator

Hello,

can't help with specifics I'm afraid, however SPT stands for Sound Powered Telephones who I believe were taken over by Redifon.

SPT originally made sound powered telephones which are used on ships as a backup means of communications, but I believe they diversified into onboard radio and TV systems.
So this may have been part of a onboard TV distrubution system, or indeed a land based system?

Mike A.

Last edited by coil1234; 22nd Nov 2022 at 2:58 pm. Reason: Changed Wording
coil1234 is offline   Reply With Quote
Old 22nd Nov 2022, 4:00 pm   #3
x72
Tetrode
 
x72's Avatar
 
Join Date: Sep 2006
Location: Chelmsford, Essex, UK.
Posts: 85
Default Re: SPT Video RF Modulator

Yes, SPT used to do distribution gear for marine use in the 1980s. They were based in Maldon, Essex. From this it looks like they were taken over by Thales after Redifon then that division was closed:
https://find-and-update.company-info...0MEL%20LIMITED
x72 is offline   Reply With Quote
Old 22nd Nov 2022, 4:08 pm   #4
winston_1
Hexode
 
Join Date: Oct 2012
Location: London, UK.
Posts: 438
Default Re: SPT Video RF Modulator

SPT were in Malden in Essex and have been gone for around 20 years now.

I have a number of these modulators and a manual somewhere. They are high output vestigial sideband modulators to almost broadcast spec. The output is around 105dBv. In your picture the left board is the power supply, the centre board is the actual modulator to BBC spec which gives an output at IF 38.9MHz vision. The module on the right is an upconverter to a (fixed) output channel. The digital display on the front panel is normally hard wired to display the output channel. Broadcast 2 to 12 and 21 to 69. Yours appears to show 88 which I think is cable channel S09. Be aware they may be setup with either a BG (5.5MHz) or I (6.0MHz) sound carrier.

Best way to test it is to connect it to an aerial input on a TV via around 30dB attenuator connect a video source and try to tune it in. Most modern TVs (except Panasonic) will tune cable frequencies, older ones may not.

Any more info required (including converting from BG to I) let me know.
winston_1 is offline   Reply With Quote
Old 23rd Nov 2022, 5:20 pm   #5
EnyaFox
Triode
 
Join Date: Mar 2022
Location: Reading, Berkshire, UK.
Posts: 32
Default Re: SPT Video RF Modulator

Quote:
Originally Posted by winston_1 View Post
SPT were in Malden in Essex and have been gone for around 20 years now.

I have a number of these modulators and a manual somewhere. They are high output vestigial sideband modulators to almost broadcast spec. The output is around 105dBv. In your picture the left board is the power supply, the centre board is the actual modulator to BBC spec which gives an output at IF 38.9MHz vision. The module on the right is an upconverter to a (fixed) output channel. The digital display on the front panel is normally hard wired to display the output channel. Broadcast 2 to 12 and 21 to 69. Yours appears to show 88 which I think is cable channel S09. Be aware they may be setup with either a BG (5.5MHz) or I (6.0MHz) sound carrier.

Best way to test it is to connect it to an aerial input on a TV via around 30dB attenuator connect a video source and try to tune it in. Most modern TVs (except Panasonic) will tune cable frequencies, older ones may not.

Any more info required (including converting from BG to I) let me know.

Could it be a possibility that one or more of the resistors on the display have gone?

I think there is also something wrong with the power supply. I am trying to figure that one out but after a while of being powered, it would trip the RCD .
EnyaFox is offline   Reply With Quote
Old 23rd Nov 2022, 5:25 pm   #6
EnyaFox
Triode
 
Join Date: Mar 2022
Location: Reading, Berkshire, UK.
Posts: 32
Default Re: SPT Video RF Modulator

Is it possible to provide more information on the power supply? Like the output voltages or resistor value?
EnyaFox is offline   Reply With Quote
Old 24th Nov 2022, 4:32 pm   #7
winston_1
Hexode
 
Join Date: Oct 2012
Location: London, UK.
Posts: 438
Default Re: SPT Video RF Modulator

The power supply is very simple. A toroidal mains transformer completely isolated with two output windings. One winding supplies a bridge rectifier, capacitor, and 18v regulator to the modulator. The other winding supplies another bridge, capacitor and -24v regulator to the upconverter. This winding also supplies an unregulated -35v supply to the display PCB.

Faulty resistors would cause display segments to go out not stay on.
Can't see how this is causing RCD trips unless the transformer is low insulation to its fixing bolt (unlikely) or possibly the mains input socket or switch.
winston_1 is offline   Reply With Quote
Old 25th Nov 2022, 5:48 pm   #8
G6ONEDave
Octode
 
G6ONEDave's Avatar
 
Join Date: Dec 2019
Location: Owston Ferry, North Lincolnshire, UK.
Posts: 1,183
Default Re: SPT Video RF Modulator

Perhaps the main input filter socket has leakage to earth causing an imbalance of live and nuetral, hence the rcd tripping.

Dave
__________________
Quote "All is hyperthetical, until it isn't!" (President Laura Roslin, Battleship Galactica)
G6ONEDave is offline   Reply With Quote
Old 28th Nov 2022, 2:09 pm   #9
EnyaFox
Triode
 
Join Date: Mar 2022
Location: Reading, Berkshire, UK.
Posts: 32
Default Re: SPT Video RF Modulator

Quote:
Originally Posted by winston_1 View Post
The power supply is very simple. A toroidal mains transformer completely isolated with two output windings. One winding supplies a bridge rectifier, capacitor, and 18v regulator to the modulator. The other winding supplies another bridge, capacitor and -24v regulator to the upconverter. This winding also supplies an unregulated -35v supply to the display PCB.

Faulty resistors would cause display segments to go out not stay on.
Can't see how this is causing RCD trips unless the transformer is low insulation to its fixing bolt (unlikely) or possibly the mains input socket or switch.
Theres a couple resistors on my power supply. I should have specified that. I will take the power supply out and see what I can find
EnyaFox is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 7:14 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2022, vBulletin Solutions, Inc.
Copyright ©2002 - 2021, Paul Stenning.