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 > Vintage Radio (domestic)

Notices

Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

Closed Thread
 
Thread Tools
Old 19th Feb 2007, 10:52 pm   #1
renato_enca
Retired Dormant Member
 
Join Date: Feb 2007
Location: Lisbon, Portugal
Posts: 51
Default Philips B3X10A - DM71 Magic Eye operation.

I'm repairing an old Philips model B3X10A, and I've noticed that the magic eye indicator type DM71 is alyaws showing "maximum signal", even if the set is completely out of tune. Before changing a open-circuited 820KOhm resistor, which feeds the magic eye (I think), that valve was always off. Could you help me find the problem?
renato_enca is offline  
Old 20th Feb 2007, 9:55 am   #2
Mike Phelan
Dekatron
 
Mike Phelan's Avatar
 
Join Date: Nov 2003
Location: Near Leeds, West Yorkshire, UK
Posts: 4,609
Default Re: Philips B3X10A - Magic Eye always on

Maybe faulty AGC decoupler or high-value resistor in AGC line?
__________________
Mike.
Mike Phelan is offline  
Old 20th Feb 2007, 10:56 am   #3
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,786
Default Re: Philips B3X10A - Magic Eye always on

I don''t actually own anything with a working DM71, but I believe these show maximum deflection with no signal, and the indicator shrinks as the signal is tuned in.

Paul
paulsherwin is online now  
Old 20th Feb 2007, 12:58 pm   #4
Dave Moll
Dekatron
 
Dave Moll's Avatar
 
Join Date: Feb 2005
Location: West Cumbria (CA13), UK
Posts: 6,118
Default Re: Philips B3X10A - Magic Eye always on

Quote:
Originally Posted by paulsherwin View Post
the indicator shrinks as the signal is tuned in.

Paul
If I recall correctly, the amount of shrinkage can be quite small!
__________________
Mending is better than Ending (cf Brave New World by Aldous Huxley)
Dave Moll is offline  
Old 20th Feb 2007, 1:12 pm   #5
Steve_P
Dekatron
 
Steve_P's Avatar
 
Join Date: Sep 2003
Location: Bolton, Greater Manchester, UK.
Posts: 6,644
Default Re: Philips B3X10A - Magic Eye always on

Yes, they are small, some would say not very good!, but used they were. I haven't got the circuit for your radio, but below is a DM70 (Similar) as used in a Tape Recorder - for what it's worth, this machine is the Elpico-Geloso model They were a 4 pin thing which looked like an Exclamation Mark.

The HT goes to the Anode, the signal to be 'measured' goes to the grid, via 0.22M Resistor, then the Diode shown. In your radio, I would check here.

Cheers,

Steve P
Attached Thumbnails
Click image for larger version

Name:	elpico1.jpg
Views:	189
Size:	19.5 KB
ID:	8360  
__________________
If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?
Steve_P is offline  
Old 21st Feb 2007, 9:42 pm   #6
renato_enca
Retired Dormant Member
 
Join Date: Feb 2007
Location: Lisbon, Portugal
Posts: 51
Default Re: Philips B3X10A - Magic Eye always on

Yes, it was a high-value resistor in the AGC line. It's a 1.5MOhm resistor, measuring 8.43MOhm. Thanks a lot!
renato_enca is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 3:57 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.