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 25th Jul 2017, 10:07 pm   #41
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Anybody recognise this "Noval" car boot find?

If that's in ohms eg: 1 ohm etc, 0.2 ohm, then that would suggest that both anode connections are in effect shorting out to the cathode connection.

Just for ref. the rectifier pinouts:

http://www.radiomuseum.org/tubes/tube_gz41.html

Lawrence.

Last edited by ms660; 25th Jul 2017 at 10:14 pm.
ms660 is offline  
Old 25th Jul 2017, 10:29 pm   #42
Wishiknewmore
Hexode
 
Join Date: Oct 2016
Location: Darlington, County Durham, UK.
Posts: 343
Default Re: Anybody recognise this "Noval" car boot find?

This may be down to my interpretation of the meter
When the probes are not connected the meter displays "1" so the first three readings I would interpret as "open"
Pins 7&8 are bridged (by design rather than accident) f and k on the radiomuseum diagram

Based on the actual valve readings would you think the rectifier is shorted internally?
Philip
Wishiknewmore is offline  
Old 25th Jul 2017, 10:39 pm   #43
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Anybody recognise this "Noval" car boot find?

In that case the last lot of readings (rectifier removed) are ok.

Do the readings with the rectifier fitted again so that we can be sure as to what's what with the rectifier valve.

Lawrence.
ms660 is offline  
Old 26th Jul 2017, 9:38 am   #44
Wishiknewmore
Hexode
 
Join Date: Oct 2016
Location: Darlington, County Durham, UK.
Posts: 343
Default Re: Anybody recognise this "Noval" car boot find?

Morning
Taken again, rectifier fitted, 200ohms setting on DMM, new battery in DMM
1&6 = 0.6
2&7 = 0.8
2&8 = 0.8
7&8 = 0.2

Hope this makes more sense to you than it does to me

Philip
Wishiknewmore is offline  
Old 26th Jul 2017, 9:48 am   #45
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Anybody recognise this "Noval" car boot find?

Now remove the rectifier valve and do the same measurements on the actual valve pins.

Lawrence.
ms660 is offline  
Old 26th Jul 2017, 10:18 am   #46
Wishiknewmore
Hexode
 
Join Date: Oct 2016
Location: Darlington, County Durham, UK.
Posts: 343
Default Re: Anybody recognise this "Noval" car boot find?

Taken again, recifier valve actual pins, 200ohms setting on DMM
1&6 = 0.7
2&7 = 0.9
2&8 = 1.0
7&8 = 0.8

Philip
Wishiknewmore is offline  
Old 26th Jul 2017, 10:21 am   #47
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Anybody recognise this "Noval" car boot find?

That suggests that the valve is shot.

Lawrence.
ms660 is offline  
Old 26th Jul 2017, 10:25 am   #48
Wishiknewmore
Hexode
 
Join Date: Oct 2016
Location: Darlington, County Durham, UK.
Posts: 343
Default Re: Anybody recognise this "Noval" car boot find?

Thanks Lawrence for your patience!
I will now see if I can source a new one!
Kind regards
Philip
Wishiknewmore is offline  
Old 26th Jul 2017, 10:41 am   #49
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Anybody recognise this "Noval" car boot find?

No problem but I can only go on the measurement readings you submit, it's unusual to have an indirectly heated rectifier with such an anode to cathode short and very unusual for both anodes to in effect read short to the cathode, but if that proves to be the case then you need to think what might have brought that on, such as an HT short etc.

Before fitting any new rectifier I would make sure there are no HT shorts and that the grid coupling capacitor to the audio output valve has been replaced.

Lawrence.
ms660 is offline  
Old 26th Jul 2017, 11:54 am   #50
high_vacuum_house
Octode
 
high_vacuum_house's Avatar
 
Join Date: May 2003
Location: Belper Derbyshire
Posts: 1,909
Default Re: Anybody recognise this "Noval" car boot find?

Looking through the glass does the electrode assembly look crooked at all. Or is there loose white cathode powder in the envelope. If there are shorts could it be the valve was dropped hard but just enough for the envelope to remain intact. A nasty bash could bend the electrodes, fracture spot welds and shift the mica separators.

Christopher Capener
__________________
Interests in the collection and restoration of Tefifon players and 405 line television
high_vacuum_house is offline  
Old 26th Jul 2017, 1:19 pm   #51
Techman
Dekatron
 
Techman's Avatar
 
Join Date: Nov 2009
Location: Lincolnshire, UK.
Posts: 4,985
Default Re: Anybody recognise this "Noval" car boot find?

You're lucky as this type of fault usually takes out the mains transformer, I've certainly had one where the two anodes shorted together across the two ends of the HT secondary of the transformer, but it still is quite unusual. In your case it seems that the transformer is fine and the valve has developed its fault only during the time that the set has been out of use - very strange!

One thing I will say is that you've really done everything in the wrong order. You should NOT have gone ahead with re-capping until you had FIRST established that the main components of the set such as mains transformer, output transformer etc. are in working order. The tests you're doing now with the lamp limiter should have been one of the FIRST tests, before any cap changing - how will you know whether you've made a possible mistake with your work if the set doesn't work once you've sorted out this rectifier fault if you don't know whether the set was capable of working in the first place?

The rule is ALWAYS the same in my book, and that is after basic static tests and checks, to get the set basically working with the minimum of work. Only then would you start replacing parts as necessary, and preferably only replacing them one at a time. I'm a fully qualified radio and TV engineer from the old days so I know what I'm talking about.
Techman is offline  
Old 26th Jul 2017, 6:57 pm   #52
Wishiknewmore
Hexode
 
Join Date: Oct 2016
Location: Darlington, County Durham, UK.
Posts: 343
Default Re: Anybody recognise this "Noval" car boot find?

Gentlemen...
Lawrence, I have replaced the grid coupling capacitor and I may have found a potential cause of the failure, the HT wire from the valve socket has a 'bareish' patch on the cloth insulation where it has rubbed against to transformer mounting screw...this has now remedied ( it was not actually shorting during testing,but it could be made to with a little pressure)
Christopher, I have looked through the class and I could convince myself of anything, but I don't have enough knowledge to tell good from bad !
Techman, I take your point, it was my original intention to replace the big electrolytics and the grid coupling capacitor before powering up, but while the soldering iron was hot I just kept going!
Thank you all for you input
My plan is to fit the 1N4007's when they arrive as Chris suggested, and if that goes well I will try with a new GZ41 - which is on order.
Any suggestions are always welcome
Philip
Wishiknewmore is offline  
Old 1st Aug 2017, 8:17 pm   #53
Wishiknewmore
Hexode
 
Join Date: Oct 2016
Location: Darlington, County Durham, UK.
Posts: 343
Default Re: Anybody recognise this "Noval" car boot find?

Update..we have progress but with some issues
I followed Chris's suggestion and tried two IN4007's , this seemed to keep the lamp limiter happy and then I moved on to a replacement GZ41 rectifier and achieved a meaningful hum
Then after connecting up a rather ad hoc antenna achieved a little more reconisable broadcasts on 3 of the 4 AM bands, but more humming than I would have hoped for

Next tied the PU input using an old iPod this works but not wonderfully, I get differing levels of hum as the volume is turned but not really proportional to the position of the potentiometer, but the hum virtually disappears on the full volume and using the volume on the iPod....
The tone controll is fairly non effective
More worrying is that I can measure about 230vdc between the chassis and the external loudspeaker socket
The PU input seems to remain connected irrespective of the wave band you chose and therefore have both radio an PU playing at the same time?

On the positive side it "works" and it is "listenable"

Bearing in mind I have replaced all the capacitors except the brown square wax cover mica(?) ones do the symptoms I describe suggest anything obvious that I may have done or any directions for my next attempt at improving it?

(don't have the correct circuit )

Many thanks
Philip
Wishiknewmore is offline  
Old 1st Aug 2017, 10:21 pm   #54
kalee99
Rest in Peace
 
Join Date: Dec 2004
Location: Newcastle Upon Tyne, Tyneside, UK.
Posts: 420
Default Re: Anybody recognise this "Noval" car boot find?

Hi,
Just a lttile idea; I had a smilar set years with no sevice information or circuit diagram at all. I got it to the stage you are at now and it had the same kind of fault.
I had changed all the waxies (so I though). It stayed on the bench for about a week just teasing me. Then I was given a head torch fpr my birthday and eager to try out this new gadget I looked at the probelematic chassis and presto; Right in one corner of the chassis and away from everything was a very dirty melted wax capacitor. It was almost dead short. It was in the tone control circuit somewhere. I replaced it and that was problem solved. Set fully working. The mark one eyeball wins again.
kalee99 is offline  
Old 3rd Aug 2017, 11:41 am   #55
Wishiknewmore
Hexode
 
Join Date: Oct 2016
Location: Darlington, County Durham, UK.
Posts: 343
Default Re: Anybody recognise this "Noval" car boot find?

Thanks Kalee for the suggestion, just the sort of thing I would do miss, but I haven't found anything lurking in corners just 50 year old dust!
I put in 15uF smoothing capacitors rather than the existing 16uF (which I don't think were original) being modern they are physically significantly smaller, could this contribute to some of my hum?
Wishiknewmore is offline  
Old 3rd Aug 2017, 12:10 pm   #56
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,526
Default Re: Anybody recognise this "Noval" car boot find?

Not as such, (15uF is well within the usual -20 +50 % tolerance of old 16uF electrolytics) but if they're wired in with any runs of wire that weren't in the original layout which are "common" to both the ripply input side and the smoothed output side then the output side will contain more hum than previously.


Think of each wire as being a 1ohm resistor and consider where any voltages generated by the ripple current through the capacitor would end up.


Another problem could be if the negative connection from capacitor to chassis is made at a different point on the chassis.
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
Herald1360 is offline  
Old 3rd Aug 2017, 12:18 pm   #57
Boater Sam
Banned
 
Join Date: Dec 2013
Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
Posts: 3,897
Default Re: Anybody recognise this "Noval" car boot find?

Pick up on the volume control if it's not earthed?
Heater wiring near a control grid?
Outer foil of a new cap on the business end rather than the low end?
Just guessing whilst sat on a straw bale, clutching.
Sam.
Boater Sam is offline  
Old 3rd Aug 2017, 1:10 pm   #58
Wishiknewmore
Hexode
 
Join Date: Oct 2016
Location: Darlington, County Durham, UK.
Posts: 343
Default Re: Anybody recognise this "Noval" car boot find?

Thanks gentlemen
Not with my radio at the moment, but almost certainly I have used alternative points of contact to the chassis than the original layout, as I have replaced one that was a chassis mounted one and I think one of the others which was not original was a can on the chassis
I will now look at my wiring in a different light
I take it means keep rippely current away from the rectified stuff!
Sam
I assume that outer foil on the business end, means have I got them the right way round?
But not sure what you mean by the "pick up on the volume control if it's not earthed?

Any thoughts about why I can read 250vdc on the extension speaker socket?

Thanks again

Philip
Wishiknewmore is offline  
Old 3rd Aug 2017, 2:30 pm   #59
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Anybody recognise this "Noval" car boot find?

""Any thoughts about why I can read 250vdc on the extension speaker socket?""

Assuming the loudspeaker circuit is floating then it could be some leakage for concern or some "leakage" not for concern, some DMM's can give funny readings if circuits are floating.

For a quick check connect something like a 47k one watt resistor between one of the extension loudspeaker sockets and chassis via a meter set to measure DC current, anything above a few microamps would normally be cause for concern.

Lawrence.
ms660 is offline  
Old 4th Aug 2017, 2:43 pm   #60
Wishiknewmore
Hexode
 
Join Date: Oct 2016
Location: Darlington, County Durham, UK.
Posts: 343
Default Re: Anybody recognise this "Noval" car boot find?

Thanks Lawrence, will do, it may be a while before I can do it but I will post findings when I do.
Philip
Wishiknewmore is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 4:03 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.