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!

Closed Thread
 
Thread Tools
Old 20th Apr 2006, 11:25 pm   #1
Michael Maurice
Moderator
 
Michael Maurice's Avatar
 
Join Date: Feb 2006
Location: Wembley, Middlesex
Posts: 7,219
Default Replacing selenium bridge rectifiers.

What is the requirement when replacing selenium bridge rectifiers? Can you just replace the rectifier with a silicon bridge rectifier or do you have to use a series resistor to mimic the forward voltage drop?

Any advice would be extremely welcome.

The equipment I'm working on is a Tandberg 74 stereo tape recorder. The mains bridge rectifier has gone S/C on one leg.
Michael Maurice is offline  
Old 20th Apr 2006, 11:29 pm   #2
Nickthedentist
Dekatron
 
Nickthedentist's Avatar
 
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,820
Default Re: Replacing selenium bridge rectifiers.

I'd do the latter, i.e. use a series R, chosen so that the HT voltage is as close to the specified value as you can get it

PS Keep up the good work with your new magazine
Nickthedentist is offline  
Old 20th Apr 2006, 11:35 pm   #3
Trish
Retired Dormant Member
 
Trish's Avatar
 
Join Date: Apr 2005
Location: Reading, Berkshire, UK.
Posts: 95
Default Re: Replacing selenium bridge rectifiers.

I'm with Nick on this one. In my past I have always included a small value resistor. Mainly to reduce the surge current.

Don't ask me why. The last one I did was well over 20 years ago.
Trish is offline  
Old 21st Apr 2006, 12:10 am   #4
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,788
Default Re: Replacing selenium bridge rectifiers.

I'd also agree, but there is actually some dispute about the necessity of adding a series resistor. Some people argue that you don't need it for current limiting purposes, and so long as the HT voltage is within limits you can just replace the selenium bridge with silicon. I always add a 200 ohm resistor though - the cost is minimal and I'm sure it's kinder on the smoothing electrolytics and other components. It reduces the peak load on the bridge, and also seems to make the HT voltage 'more or less' right.

Best regards, Paul
paulsherwin is online now  
Old 21st Apr 2006, 12:44 am   #5
Alf
Hexode
 
Alf's Avatar
 
Join Date: May 2005
Location: Wigan, Greater Manchester, UK.
Posts: 479
Default Re: Replacing selenium bridge rectifiers.

Not exactly a bridge rectifier but, I remember in the early 1960s, I replaced the infamous Mazda U801 valve on an Ekco tv with a BY100 silicon rectifier and was advised to place a 25 ohm 10w w/w resistor in series with it, this I did, the increase in brightness and contrast on the screen was phenomenal and nothing overheated.
Alf is offline  
Old 21st Apr 2006, 8:36 am   #6
Mike Phelan
Dekatron
 
Mike Phelan's Avatar
 
Join Date: Nov 2003
Location: Near Leeds, West Yorkshire, UK
Posts: 4,609
Default Re: Replacing selenium bridge rectifiers.

In the far distant past, when the then new BY100 appeared to solve the world's problems, or at least the smell of sewage from a failing selenium reccy, it arrived as a kit from Radiospares with a 5w 10 (?) ohm wirewound.

U801, eh? Almost nice enough to put on your mantelpiece!
__________________
Mike.
Mike Phelan is offline  
Old 5th Jun 2006, 9:28 pm   #7
zak
Retired Dormant Member
 
Join Date: Feb 2005
Location: Monmouthshire,on South Wales border
Posts: 85
Default Re: Replacing selenium bridge rectifiers.

I would alays add a resistor to limit the surge current,this is important.Also often necessary is a small value cap across each diode,otherwise the spikes create modulation hum.
zak is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 4:20 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 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.