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 > General Vintage Technology > Success Stories

Notices

Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

Reply
 
Thread Tools
Old 31st Dec 2019, 4:02 pm   #21
Beardyman
Pentode
 
Beardyman's Avatar
 
Join Date: Jan 2018
Location: Portsmouth, Hampshire, UK.
Posts: 166
Default Defiant MSH902 addendum

Having completed this restoration some time earlier this year I thought I would fire up the radio over the Christmas period just to make sure everything was ok. It was, for about 20-30 minutes, then gradually started to lose the bass notes & grow quieter. This was something I thought I had fixed previously but obviously I hadn't!?! As this set doesn't have any circuit diagrams available (apart from my own hand written ones) & dozens of photos I took prior to any work being carried out I thought I'd spend an hour or two correllating the two. It wasn't unitl I had the chassis out of the case (again) that I was idly prodding around the resistors attached to the FC4 valve that I found a dodgy reading. There was supposed to be a 500K strapped across pins 2 & 6 (g1 & k), mine was reading 50K! This was a case of mistaken identiity, entriely my fault but a quick glance & it "looks" like a 510K. The body is painted a brick red & the gold tolerance band looks yellow under anything but a bright white light. Needless to say the orange band is nearly invisible against the body. I changed it for the correct value & now the set is booming nicely & has been for well over 3 hours, looks like the FC4 survived. Tough things these valves!
__________________
The difference between stupidity and genius is that genius has its limits. (Einstein)
Beardyman is offline   Reply With Quote
Old 31st Dec 2019, 4:33 pm   #22
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 8,688
Default Re: Defiant MSH902

So what was the correct value?

Lawrence.
ms660 is online now   Reply With Quote
Old 31st Dec 2019, 6:05 pm   #23
Beardyman
Pentode
 
Beardyman's Avatar
 
Join Date: Jan 2018
Location: Portsmouth, Hampshire, UK.
Posts: 166
Default Re: Defiant MSH902

500K Lawrence. Have a good evening & New Year.
__________________
The difference between stupidity and genius is that genius has its limits. (Einstein)
Beardyman is offline   Reply With Quote
Old 31st Dec 2019, 6:32 pm   #24
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 8,688
Default Re: Defiant MSH902

500k between osc grid and cathode seems high to me:

http://www.r-type.org/pdfs/fc4.pdf

Lawrence.
ms660 is online now   Reply With Quote
Old 9th Jan 2020, 9:34 pm   #25
Beardyman
Pentode
 
Beardyman's Avatar
 
Join Date: Jan 2018
Location: Portsmouth, Hampshire, UK.
Posts: 166
Default Re: Defiant MSH902

Yes it does but I've been going through the photos I took before any work was carried out & the original resistor was a 500K across pins 2 & 6. I've also been looking through various other schematics of radios that use the FC4 (theres a fair few!) & the highest value I've found in those was 100K in an EKCO set. Unlike the valve museum datasheet the Defiant has that 500K across 2 & 6 but also a 250R with 0.1uf in parallel to chassis from pin 6 (k). I don't have enough knowledge of valves to unpick the designers thoughts on this one but the radio now works as it should. I'm sure there are other members who may shed some light on this toothsome feature.
Attached Thumbnails
Click image for larger version

Name:	fc4-orig.jpg
Views:	45
Size:	83.2 KB
ID:	196802  
__________________
The difference between stupidity and genius is that genius has its limits. (Einstein)
Beardyman is offline   Reply With Quote
Old 10th Jan 2020, 3:46 pm   #26
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 8,688
Default Re: Defiant MSH902 addendum

Quote:
Originally Posted by Beardyman View Post
There was supposed to be a 500K strapped across pins 2 & 6 (g1 & k), mine was reading 50K! This was a case of mistaken identiity, entriely my fault but a quick glance & it "looks" like a 510K. The body is painted a brick red & the gold tolerance band looks yellow under anything but a bright white light. Needless to say the orange band is nearly invisible against the body. I changed it for the correct value & now the set is booming nicely & has been for well over 3 hours, looks like the FC4 survived. Tough things these valves!
You say it looks like a 510k but then you say the body is red....

A 500k (ish) resistor going down to 50k in that circuit position I find very hard to believe unless it's had the wrong colour code painted on it....

I suspect the original that was fitted was either a 50k or 56k, I would go for 50k.

Lawrence.
ms660 is online now   Reply With Quote
Old 15th Jan 2020, 8:14 am   #27
The Avery Man
Diode
 
Join Date: Jun 2019
Location: Birmingham, West Midlands, UK.
Posts: 3
Default Re: Defiant MSH902

Can you advise the contact details for the co-op archive as I am looking for a circuit for a Defiant MSH547. Thanks
The Avery Man is offline   Reply With Quote
Old 15th Jan 2020, 1:48 pm   #28
Beardyman
Pentode
 
Beardyman's Avatar
 
Join Date: Jan 2018
Location: Portsmouth, Hampshire, UK.
Posts: 166
Default Re: Defiant MSH902

The Avery Man,

The email address is on the Co-Op Archive website but does take a little rooting around to find so here it is: archive@co-op.ac.uk

When I contacted them their reply was as follows:

"I am afraid we do not have service sheets for any of the radios before the 1950s. The collection of material we hold on the CWS manufacture of radios and televisions is small and includes some catalogues of products from the 1930s. There are also handwritten notebooks with information about individual models. These show that the Model MSH 902 came in two versions - AC and AC-DC and were first introduced during the 1935-36 season."

I'd have said that you may find yourself in the same position as myself, no circuits other than what you may be able to come up with, I have looked on my copy of the Vintage Radio Service Data DVD & there's nothing there either.

Best of luck sir!
__________________
The difference between stupidity and genius is that genius has its limits. (Einstein)
Beardyman is offline   Reply With Quote
Old Today, 9:40 pm   #29
Beardyman
Pentode
 
Beardyman's Avatar
 
Join Date: Jan 2018
Location: Portsmouth, Hampshire, UK.
Posts: 166
Default Re: Defiant MSH902

Final (hopefully!) addendum to this thread. This radio has always had a rustling noise in the background on MW/LW, sometimes there would be an odd phasing then back to normal or random pops/clicks. I, in my ignorance, thought initially it was simply down to the age of the valves and/or coils, after all it is nearly 90 years old having been manufactured in around 1933-34. To have some noise would be forgiveable BUT it was irritating! Then I started trawling through this forum & others for the possible causes of it. It took many hours of reading but finally a trend began appearing especially in America of all places. It would seem the mica capacitor is suffering the effects of time. I then found a paper published in 1960(!) giving a LOT of detail as to their failure modes, one of which is silver migration & inclusions in the mica itself. I'm not at all sure if the document is still within copyright so I have not attached it here. The link is: https://www.google.com/url?sa=t&rct=...10e6UqL2TWJLvf
Anyway, I was becoming more convinced this was perhaps what was still wrong with the Defiant. I remembered I had left one mica capacitor in the aerial side of things. Out came the chassis, it looked good, tested ok as well, bang on value. Grab a replacement from the stock of caps, out with the old & in with the new! Switched on, the rustling/popping/f*rting had gone! It sounds so much better.
__________________
The difference between stupidity and genius is that genius has its limits. (Einstein)
Beardyman is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 11:26 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.