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

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Amateur and Military Radio

Notices

Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

Closed Thread
 
Thread Tools
Old 25th Nov 2018, 8:00 pm   #21
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 8,817
Default Re: Wireless Set 19 repairs question.

Sympathetic capacitor- and where-necessary resistor-replacement too is sensible.

In particular the screen-bypass capacitors and their associated resistors. The resistors often drift high by up to 50% and if the decoupling capacitors are also leaky they can pull the screen-voltage down significantly causing loss-of-gain.

AGC-line decouplers (both R and C) are also candidates for attention: though the voltages are relatively low, any increased resistance or capacitor-leakage can cause overloading of some stages because the full AGC doesn't get to where it's needed.

There's also a couple of decouplers associated with the VFO and the BFO: when these become aged the continuous slight variation in leakage causes 'scintillation' - random relatively rapid wobbles or wandering of the BFO/VFO that can really spoil the pleasure of using the radio.

I also once 'fixed' a WS19 that had a significant frequency-drift issue by replacing one of the under-chassis coax interconnects. The braid had suffered the dreaded 'green' corrosion under the outer jacket.
G6Tanuki is online now  
Old 26th Nov 2018, 9:39 am   #22
G4YVM David
Heptode
 
G4YVM David's Avatar
 
Join Date: May 2014
Location: Salisbury, Wiltshire, UK.
Posts: 886
Default Re: Wireless Set 19 repairs question.

Thanks all, a comprehensive set of answers. I will check some of those caps because 'effects' listed ring bells with some 'faults' found...notable low gain and a very dodgy AGC / AVC system.

Currently feeding heaters from DC hence the diodes, one of which is shot.

I shall keep you all informed of further progress.

David
G4YVM David is online now  
Old 26th Nov 2018, 9:46 am   #23
G4YVM David
Heptode
 
G4YVM David's Avatar
 
Join Date: May 2014
Location: Salisbury, Wiltshire, UK.
Posts: 886
Default Re: Wireless Set 19 repairs question.

Quote:
Originally Posted by Orakle42 View Post
If this 12v supply is feeding the heaters the startup I is quite high.
In a similar application I have used either 10A10 series (wire ended) or chassis mount bridges like the KBPC25-04, they are almost indestructible in this type of application. It may have been the turn on surge that killed the original diode.

Orakle42
When you say 'quite high', what did you cater for?

David
G4YVM David is online now  
Old 26th Nov 2018, 4:54 pm   #24
Orakle42
Tetrode
 
Join Date: Nov 2015
Location: Maidstone, Kent, UK.
Posts: 92
Default Re: Wireless Set 19 repairs question.

Hi David

I will rummage through my records and try to find the appropriate notes, it may take a few days. My notes relate to a Mk 2 set that has had the "b" set & intercom parts removed. I believe the remaining parts are similar to the Mk3.
Will reply again soon when data found. Do the diodes fitted have any form of ID?

Orakle42
Orakle42 is offline  
Old 26th Nov 2018, 6:01 pm   #25
Orakle42
Tetrode
 
Join Date: Nov 2015
Location: Maidstone, Kent, UK.
Posts: 92
Default Re: Wireless Set 19 repairs question.

Hi David

My records show that starting I at 12.6v DC for the A set only was 8 to 10 amps with a 0.01 series resistor. It settled after about 10 seconds at a nominal 1.9 - 2.0 amps. This coincides with the theoretical figure of 1.8 anps. If the IC valves are still present this would be slightly higher. I do not have a Mk3 circuit diagram but I assume it will be similar with 2 x 0.3 amp heaters in series. I opted for overkill on the diodes on a previous rectifier situation hence my suggestion for the 10a10 series which have a 6 amp
forward rating. The lower rated 1N54** series at 3 amps might suffice but you would have to check the surge current rating and the steady state power derating.

Hope this helps.

Orakle42
Orakle42 is offline  
Old 27th Nov 2018, 12:11 am   #26
G4YVM David
Heptode
 
G4YVM David's Avatar
 
Join Date: May 2014
Location: Salisbury, Wiltshire, UK.
Posts: 886
Default Re: Wireless Set 19 repairs question.

Thanks for that info. I had calculated 10amps max from the circuit so Im.glad I was nearby. My set also has the B set (and i/c as far as i can see) removed.

My diodes are.completely blank. Ive never understood why manufacturers make itwms with no ident on them at all. It must confuse even themselves.

Thanks again

David
G4YVM David is online now  
Old 5th Dec 2018, 11:48 am   #27
G4YVM David
Heptode
 
G4YVM David's Avatar
 
Join Date: May 2014
Location: Salisbury, Wiltshire, UK.
Posts: 886
Default Re: Wireless Set 19 repairs question.

Ive replaced the diodes with a bridge recitifer...15 amps, plenty of headroom. However, on measuring I find that I put 21 volts AC into two of the corners but get 21v DC out of the others!! Clearly this is both too much for heaters and too much for the BR to be correctly working or wired. Any thoughts on what might be wrong here??
G4YVM David is online now  
Old 5th Dec 2018, 6:14 pm   #28
Orakle42
Tetrode
 
Join Date: Nov 2015
Location: Maidstone, Kent, UK.
Posts: 92
Default Re: Wireless Set 19 repairs question.

Hi David

If the transformer has a center tapped winding of 12-0-12 configuration the center should be to ground and the 2 12v connections to the bridge ac terminals. The bridge +VE output will be approx +12v off load relative to ground. Ignore the bridge -ve output which will be about -12v and leave floating. I understand from your earlier posts that only 2 diodes were present previously which would suggest that this is the rectifier configuration you have which is a standard bi-phase rectifier circuit. The use of the bridge usually eases installation and allows bolting to the chassis as a heatsink.
The negative arms are redundant unless you need a -ve supply.

Good luck!

Orakle42
Orakle42 is offline  
Old 5th Dec 2018, 7:20 pm   #29
G4YVM David
Heptode
 
G4YVM David's Avatar
 
Join Date: May 2014
Location: Salisbury, Wiltshire, UK.
Posts: 886
Default Re: Wireless Set 19 repairs question.

That's it! Thanks.

All heaters glowing now. Just the audio transformer to sort so that a speaker may be used.


David
G4YVM David is online now  
Old 5th Dec 2018, 7:32 pm   #30
Orakle42
Tetrode
 
Join Date: Nov 2015
Location: Maidstone, Kent, UK.
Posts: 92
Default Re: Wireless Set 19 repairs question.

Hi David

I thought the attached would be clearer but you appear to have hacked it OK, well done!
I assume that the meter now reads the correct battery voltage on the LT setting. As a matter of interest what is the DC voltage with the heaters on?

Orakle42
Attached Files
File Type: pdf PSU.pdf (248.7 KB, 39 views)
Orakle42 is offline  
Old 5th Dec 2018, 11:43 pm   #31
G4YVM David
Heptode
 
G4YVM David's Avatar
 
Join Date: May 2014
Location: Salisbury, Wiltshire, UK.
Posts: 886
Default Re: Wireless Set 19 repairs question.

10.9v at the rectifier, vs 13v when heaters off
G4YVM David is online now  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 8:04 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 - 2020, vBulletin Solutions, Inc.
Copyright ©2002 - 2020, Paul Stenning.