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 > General Vintage Technology > Hints, Tips and Solutions (Do NOT post requests for help here)

Notices

Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

Reply
 
Thread Tools
Old 20th Jun 2022, 5:56 pm   #1
Viscount
Heptode
 
Join Date: Jan 2018
Location: Folkestone, Kent, UK.
Posts: 569
Default Roberts R800 switch.

so my old r800 has been sitting on the shelf long enough now with an intermittent on /off switch which ive heard off a few times ,its a rather flimsy design really considering the use it gets ,its a small push on /off effort,why they didnt use a switched pot i will never know,anyway back to the problem,i removed the chassis from the cabinet and tryed some switch cleaner to no avail,the prob is still there ie any slight touch of the switch and the set goes off,so looking at the underside of the circuit board i see only 2 of the switch pins are used (no suprise)so i bridged those with the opposite unused ones and hey presto perfect 1 R800 working as it should
Viscount is offline   Reply With Quote
Old 21st Jun 2022, 1:05 pm   #2
Heatercathodeshort
Dekatron
 
Heatercathodeshort's Avatar
 
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,103
Default Re: roberts R800

This was a very common fault with the Roberts R800 and R900. A look at the circuit will reveal C167 1500uf connected across the DC switched side from the battery/mains unit.
Switching on produces a very heavy surge and spark at the switch contacts burning them out.
The so called cure was to replace the cap, a 470uf in the R900 with 47uf. It hummmmmed! There was no other suggestion from Roberts at the time. Reducing the value of C167 in the R800 may prolong the life of the switch but it will fail again. The switch was part of a push button waveband switch in the R900. It was horrible to change!

I had a very difficult time with my customers with the 800 and 900 that led me to letting the Roberts agency go. John.
Heatercathodeshort is offline   Reply With Quote
Old 21st Jun 2022, 4:48 pm   #3
buggies
Heptode
 
buggies's Avatar
 
Join Date: Jan 2009
Location: West Lothian, UK.
Posts: 695
Default Re: roberts R800

Wire the capacitor to the other side of the switch??
__________________
George
buggies is offline   Reply With Quote
Old 21st Jun 2022, 6:50 pm   #4
Viscount
Heptode
 
Join Date: Jan 2018
Location: Folkestone, Kent, UK.
Posts: 569
Default Re: roberts R800

yes its an awful design really but as i said in the op linking with 2 unused contacts opposite solves the prob ,although it will prob go the same way as before but should last a while i hope
Viscount is offline   Reply With Quote
Old 21st Jun 2022, 7:03 pm   #5
Heatercathodeshort
Dekatron
 
Heatercathodeshort's Avatar
 
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,103
Default Re: roberts R800

Yes George, there were a few mods but I think it suffered from very short battery life when wired before the switch. I think there were some related problems also. It is a long time ago. The R900 sounded great as a mains portable. John.
Heatercathodeshort is offline   Reply With Quote
Old 22nd Jun 2022, 9:00 pm   #6
radio69
Tetrode
 
Join Date: May 2022
Location: Hangleton, (Hove) East Sussex. UK.
Posts: 61
Default Re: Roberts R800 switch.

I think the R800 should receive an award as possibly the worst Roberts set ever.....
Dreadful things...
radio69 is offline   Reply With Quote
Old 26th Jun 2022, 5:26 am   #7
FrankB
Heptode
 
Join Date: Oct 2005
Location: Olympia, Washington, USA.
Posts: 605
Default Re: Roberts R800 switch.

I might like to suggest adding a relay in place of the switch contacts. Use the switch contacts to activate the coil of the relay.
Back when I was servicing and parts were available, I would wire both switch halves in parallel on the DPST control switches or add a relay.
FrankB is offline   Reply With Quote
Old 2nd Jul 2022, 2:27 pm   #8
Philips210
Nonode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,235
Default Re: Roberts R800 switch.

Frank's suggestion looks a good solution to the problem. I am also all for doubling up on the switch contacts if possible to spread the current flow for best contact life.

On a similar note maybe a power MOSFET to carry the radios's supply current is another idea. I built a bedside timer for my late father's Roberts R701 radio which used a MOSFET to control the radio's supply. From memory the circuit was in September 2000 EPE magazine. I think it was a circuit provided by a reader.

Regards,
Symon
Philips210 is offline   Reply With Quote
Old 25th Nov 2022, 9:47 pm   #9
PaulDarzi
Tetrode
 
Join Date: Nov 2022
Location: Near Worcestershire/Gloucestershire border (in WR), UK.
Posts: 60
Default Re: Roberts R800 switch.

Quote:
Originally Posted by Philips210 View Post
Frank's suggestion looks a good solution to the problem. I am also all for doubling up on the switch contacts if possible to spread the current flow for best contact life.

On a similar note maybe a power MOSFET to carry the radios's supply current is another idea. I built a bedside timer for my late father's Roberts R701 radio which used a MOSFET to control the radio's supply. From memory the circuit was in September 2000 EPE magazine. I think it was a circuit provided by a reader.

Regards,
Symon
Wow, superb memory Symon!

Page 679 of EPE September 2000 indeed has a reader provided "Radio sleep timer" - with their values for about an hour, with a neat 3.5mm plug+socket arrangement that allows it to be disconnected leaving normal operation, very nice.

The actual switching uses a BUZ71A MOSFET as you accurately recalled - am going to use this idea (with different components) to help a sickly Roberts as suggested.
PaulDarzi is offline   Reply With Quote
Old 26th Nov 2022, 8:54 pm   #10
Philips210
Nonode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,235
Default Re: Roberts R800 switch.

Hello Paul,

It's a neat little circuit that works very well and has been totally reliable.

With my dad's timer unit, I didn't make any alterations to his R701 radio. The timer circuit together with a PP9 battery was built in a diecast box which was external to the radio. The timed supply from the box simply feeding the radio's dc power jack. On the box were mounted two momentary push to make switches for starting and stopping the timed supply. I made a slight change to the circuit so it gave around thirty minutes before switching off.

The timer circuit could no doubt be built into the radio but mounting the switches without spoiling the originality of the radio could be a challenge.
I suppose the circuit could be easily adapted to give simple on/off operation without timed operation or have both as an option.

Regards,
Symon
Philips210 is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 7:24 am.


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 - 2023, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.