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 3rd Jun 2020, 5:48 pm   #1
richieyork
Pentode
 
richieyork's Avatar
 
Join Date: Dec 2010
Location: York, North Yorkshire, UK.
Posts: 212
Default Sonora SF5 - Low HT

Hi all

This is a follow up after a request for a circuit diagram for this French radio. I now have it thanks to help on this site

OK, so its from 1936.

Quick cold checks no obvious shorts on primary side and visuals looked ok though noted the original "42" model output valve had been replace by an EL84 some time back. The original socket is in place, looks like the base of the old valve retained and a B9A (?) socket with EL84 mounted.....no attempts seem to have been made re circuit component value changes.

Anyway gave it a gentle start with a bulb limiter (100w bulb). Valves glowing and faint crackle from the speaker when volume control twiddled.

Voltage checks on secondary of mains tranny giving just over 300v on each side of the winding ie 2 x 300v to the "80" full wave rectifier valve. However, the DC from the valve was a lowly 34 volts. I disconnected ALL the loading on the DC side of the valve (except the filter cap) and it bumped up to about 270v. As soon as I connect in the output valve or the earlier stages of the set the voltage plummets again.

I've checked the other HT DC feeds to the remains of the set and no shorts apparent or anything getting obviously hot.

Forgive my ignorance here but can rectifier valves give a good output but plummet when on load due to the valve being worn out?? Unfortunately I don't have a valve tester and was gonna stick a couple of 1N4xxx silicon rectifier diodes in place of the 80 valve but unsure what resistor I should use to drop the volts sufficiently for the set.

Please see attached pics and screen snip of power supply.

Any thoughts please??
Kind regards
Rich
Attached Thumbnails
Click image for larger version

Name:	Sonora power supply.PNG
Views:	102
Size:	39.2 KB
ID:	207561   Click image for larger version

Name:	20200603_082524.jpg
Views:	81
Size:	35.1 KB
ID:	207562   Click image for larger version

Name:	20200603_082535.jpg
Views:	66
Size:	44.7 KB
ID:	207563  
richieyork is offline  
Old 3rd Jun 2020, 5:57 pm   #2
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,526
Default Re: Sonora SF5 - Low HT

With NO load on the HT and 300Vac on the rectifier anodes, I'd expect 400V+ on the reservoir cap. Does sound like a very tired 80.

A couple of 1N4007s and say 220R 5W should be OK IF the reservoir and smoothing capacitors are rated at least 450V and in good health... use a lamp limiter too for initial investigations!
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
Herald1360 is offline  
Old 3rd Jun 2020, 9:10 pm   #3
richieyork
Pentode
 
richieyork's Avatar
 
Join Date: Dec 2010
Location: York, North Yorkshire, UK.
Posts: 212
Default Re: Sonora SF5 - Low HT

Thanks Herald1360 - i've found a new old stock "80" at Langrex for a tenner so ordered it anyway as i think your suspicions are correct re the valve not being able to deliver some oomph. I'll try the diodes+resistor option anyway - the reservoir cap is 500V rated and i've broken it in gently via the limiter. I'll retain the limiter for testing.
richieyork is offline  
Old 3rd Jun 2020, 9:34 pm   #4
crackle
Rest in Peace
 
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
Default Re: Sonora SF5 - Low HT

A radio of this age is almost certainly going to need the audio coupling capacitor to the grid of the OP valve changed in order to stop DC leakage onto the grid of the OP valve.
The other problem is going to be leakage in the smoothing capacitors, this will have the effect of pulling too much current through the energising coil and causing the voltage to drop.
I would advise rectifying those issues before you put another more capable rectifier into the radio. Or you may find the higher current capabilities of the new valve will be enough to damage the speaker energising coil or the output transformer, or the mains transformer secondary.

What made you choose to identify your radio as an SF5, as that radio appears to have 3 bars across the speaker whereas yours has 2 bars.

Mike
crackle is offline  
Old 3rd Jun 2020, 9:47 pm   #5
turretslug
Dekatron
 
turretslug's Avatar
 
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,385
Default Re: Sonora SF5 - Low HT

I think it would be a wise move also to replace the 0.02uF capacitor between the anode of the output valve and 0V- if this fails, the output transformer, field coil (exc dyn) speaker, rectifier and mains transformer are all in serious jeopardy. A 1kV rated capacitor should be used to give a healthy margin of DC HT + peak AC excursion. Sorry if the replacement list is starting to build up, but it's still cheap insurance.
turretslug is offline  
Old 4th Jun 2020, 1:10 am   #6
Tim
Dekatron
 
Tim's Avatar
 
Join Date: Jan 2003
Location: Bradford on Avon, Wiltshire, UK.
Posts: 3,301
Default Re: Sonora SF5 - Low HT

You could test the rectifier with something like a 15W pigmy bulb. That would represent a load approximating to an average set.
__________________
"Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."
Tim is offline  
Old 4th Jun 2020, 7:32 am   #7
crackle
Rest in Peace
 
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
Default Re: Sonora SF5 - Low HT

Quote:
Originally Posted by richieyork View Post
..........can rectifier valves give a good output but plummet when on load due to the valve being worn out?? Unfortunately I don't have a valve tester and was gonna stick a couple of 1N4xxx silicon rectifier diodes in place of the 80 valve but unsure what resistor I should use to drop the volts sufficiently for the set.
In answer to your question, yes I am sure they can. But I would advise making the other checks and changing the obvious suspect capacitors before putting in a rectifier that could provide enough current to rip through the transformer windings.

Mike
crackle is offline  
Old 4th Jun 2020, 8:42 am   #8
richieyork
Pentode
 
richieyork's Avatar
 
Join Date: Dec 2010
Location: York, North Yorkshire, UK.
Posts: 212
Default Re: Sonora SF5 - Low HT

Quote:
Originally Posted by crackle View Post
A radio of this age is almost certainly going to need the audio coupling capacitor to the grid of the OP valve changed in order to stop DC leakage onto the grid of the OP valve. Done
The other problem is going to be leakage in the smoothing capacitors, this will have the effect of pulling too much current through the energising coil and causing the voltage to drop. This has been checked and reformed
I would advise rectifying those issues before you put another more capable rectifier into the radio. Or you may find the higher current capabilities of the new valve will be enough to damage the speaker energising coil or the output transformer, or the mains transformer secondary. Working my way through replacing the paper caps

What made you choose to identify your radio as an SF5, as that radio appears to have 3 bars across the speaker whereas yours has 2 bars.

Mike
Mike - see my progress above. Cheers. Taking it gently. Yes, think I got the model number wrong.....it could be a VM1. Well spotted. I alighted on the SF5 after lots of searching and RadioMuseum showed same chassis/valve line up. The style is distinctive but I missed out one of the horizontal chrome bars on the speaker...Doh. But the chassis appears to be the same and the circuit diagram seems to match mine.
richieyork is offline  
Old 4th Jun 2020, 8:50 am   #9
richieyork
Pentode
 
richieyork's Avatar
 
Join Date: Dec 2010
Location: York, North Yorkshire, UK.
Posts: 212
Default Re: Sonora SF5 - Low HT

Quote:
Originally Posted by turretslug View Post
I think it would be a wise move also to replace the 0.02uF capacitor between the anode of the output valve and 0V- if this fails, the output transformer, field coil (exc dyn) speaker, rectifier and mains transformer are all in serious jeopardy. A 1kV rated capacitor should be used to give a healthy margin of DC HT + peak AC excursion. Sorry if the replacement list is starting to build up, but it's still cheap insurance.
Interestingly enough that particular capacitor had blown up at some point. It was used with a switch on the back of the set to offer treble cut I think (not shown in the circuit snipping - my model differs slightly, see later post from me). The switch contacts had blown too. I 'think' that's what had led to the demise of the original output valve and subsequent replacement by an EL84..I can confirm the field windings are intact however.

Is it safe to leave it out of the circuit altogether, given the switch it's associated with is knackered?
richieyork is offline  
Old 4th Jun 2020, 9:08 am   #10
vinrads
Dekatron
 
Join Date: Feb 2009
Location: Chesterfield, Derbyshire, UK.
Posts: 3,737
Default Re: Sonora SF5 - Low HT

Yes leave it out for now , as I suggested replace all the paper capacitors ,and poss the smoothing , I have a full circuit and layout , of the two bar one vm1. it looks like the output could be an 80 or a 6f6 . .Mick.
vinrads is offline  
Old 4th Jun 2020, 9:26 am   #11
richieyork
Pentode
 
richieyork's Avatar
 
Join Date: Dec 2010
Location: York, North Yorkshire, UK.
Posts: 212
Default Re: Sonora SF5 - Low HT

Mick, the output valve is a 42 but was replaced at some point in the past with an EL84...though the original valveholder is intact. It seems from a quick look on interweb that 42 valves are quite hard to find (and probably expensive...). Is a 6f6 a direct pin for pin substitute/equivalent

The repairer doesn't seem to have changed any of the other components in the output circuit so i'm not sure the EL84 is 'right' for the job, but we'll see...
richieyork is offline  
Old 4th Jun 2020, 10:03 am   #12
vinrads
Dekatron
 
Join Date: Feb 2009
Location: Chesterfield, Derbyshire, UK.
Posts: 3,737
Default Re: Sonora SF5 - Low HT

Sorry I don't know what happened there I know 80 is the rectifier ,It would be nice to restore it back to factory, I may have a 42 will let you know ,Mick.

Good news I have a few 42's I can let you have one tested 100% £7 inc p/p PM me with your posting details , if you want it , I noticed the 6f6 is octal ie not the same base as the 42 , Mick.

Last edited by vinrads; 4th Jun 2020 at 10:22 am.
vinrads is offline  
Old 4th Jun 2020, 10:27 am   #13
crackle
Rest in Peace
 
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
Default Re: Sonora SF5 - Low HT

The capacitor from the anode of the OP valve to ground (the one that has blown up in your case) is I believe referred to as the tone correction capacitor. It has two functions, to reduce treble in the audio output, you sometimes see it connected via a variable resistor to give full tone control.
Another function is I believe to help stop any unwanted oscillation that might occur in the OP stage. In this case a safer way to connect the capacitor is across the primary of the OP transformer, rather than from the anode to ground.

Mike
crackle is offline  
Old 4th Jun 2020, 11:29 am   #14
richieyork
Pentode
 
richieyork's Avatar
 
Join Date: Dec 2010
Location: York, North Yorkshire, UK.
Posts: 212
Default Re: Sonora SF5 - Low HT

Quote:
Originally Posted by crackle View Post
The capacitor from the anode of the OP valve to ground (the one that has blown up in your case) is I believe referred to as the tone correction capacitor. It has two functions, to reduce treble in the audio output, you sometimes see it connected via a variable resistor to give full tone control.
Another function is I believe to help stop any unwanted oscillation that might occur in the OP stage. In this case a safer way to connect the capacitor is across the primary of the OP transformer, rather than from the anode to ground.

Mike
Good point, Mike. I'm thinking high voltage cap needed here. Where's a good source of 1000v(??) caps for this purpose please??
richieyork is offline  
Old 4th Jun 2020, 11:46 am   #15
crackle
Rest in Peace
 
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
Default Re: Sonora SF5 - Low HT

here is one, https://uk.farnell.com/vishay/s223m7...z5u/dp/2860155
But I would try a .01uf as I always find the tonal quality is better with a little more treble.
Mike
crackle is offline  
Old 17th Jun 2020, 10:13 am   #16
richieyork
Pentode
 
richieyork's Avatar
 
Join Date: Dec 2010
Location: York, North Yorkshire, UK.
Posts: 212
Post Re: Sonora SF5 - Low HT

Hi everyone
OK, update on the Sonora radio.
Thanks to Langrex and a kindly chap on here i've got replacement full wave rectifier and audio output valves back into the chassis.
I now have a set that's working 'sort of'...
  • Possibly too much HT
  • The energised loudspeaker cone dragging
  • Silent medium wave
  • Lots of background static on top of any station

So, HT. Both my DMM and analogue meters are giving 345v DC on the cathode of the CV1708 f/w rectifier valve - this drops to around 294v on the anode of the output valve. The CV1708 replaced the original "80" valve - I was advised this was a suitable substitute (not on this website)... This voltage seems high. Any thoughts and/or suggestions on how to tame it? which 'may be answered by the next issue.

The speaker cone is dragging - it's an energised coil speaker (not permanent magnet) and tbh I don't currently have time or patience to try and sort it out. I do have a permanent magnet speaker that would fit. If I ditched the original speaker what sort of resistor ohm/rating might be good to try? I'm also linking this with the high HT above.

Medium wave is quiet. The set uses a strange set of 12 rotating cams across 12 contacts to change waveband so i'm trying to see if some aren't making contact. Wafer switches are so much easier!

Long wave pulls in RTE and R4 but both are buried under a lot of static. I'm using around 7ft of wire for the aerial. I guess it needs more??

All paper caps have been changed for new ones and resistors checked though most were within 20%.

Cheers
Rich
Attached Thumbnails
Click image for larger version

Name:	Sonora wave change.PNG
Views:	40
Size:	27.3 KB
ID:	208682   Click image for larger version

Name:	Sonora power supply.PNG
Views:	37
Size:	39.2 KB
ID:	208683  

Last edited by richieyork; 17th Jun 2020 at 10:22 am.
richieyork is offline  
Old 17th Jun 2020, 2:16 pm   #17
PJL
Dekatron
 
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
Default Re: Sonora SF5 - Low HT

It will be far easier to fix the speaker than change to a permanent magnet one. Did you replace the suppression capacitors across the mains input with class Y types? Is the speaker in the set original?

Is it set for 250V? The high HT volts may in part be due to a later generation 80 valve but high HT normally means the set is not taking enough HT current. Check the value of the output valve cathode resistor then measure the cathode voltage so you can work out the current.
PJL is offline  
Old 17th Jun 2020, 2:33 pm   #18
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,192
Default Re: Sonora SF5 - Low HT

Is the voltage selector correctly set?

What's the AC voltage on the HT secondary of the mains transformer?

Resistance of HT Choke/speaker energising coil?
__________________
Graham. Forum Moderator

Reach for your meter before you reach for your soldering iron.
Station X is offline  
Old 17th Jun 2020, 2:58 pm   #19
richieyork
Pentode
 
richieyork's Avatar
 
Join Date: Dec 2010
Location: York, North Yorkshire, UK.
Posts: 212
Default Re: Sonora SF5 - Low HT

Quote:
Originally Posted by PJL View Post
It will be far easier to fix the speaker than change to a permanent magnet one. Did you replace the suppression capacitors across the mains input with class Y types? Is the speaker in the set original?
Yep both suppression caps replaced with new ones.

The speaker looks to be the original. I'm put off trying to repair it as i'm unsure how to with this type of cone assembly - i've done a few hifi speaker re-centerings but this one has a centre piece that looks like a 45rpm record centre adaptor that's held down by a screw. How can I safely remove that from the cone?

Quote:
Originally Posted by PJL View Post
Is it set for 250V? The high HT volts may in part be due to a later generation 80 valve but high HT normally means the set is not taking enough HT current. Check the value of the output valve cathode resistor then measure the cathode voltage so you can work out the current.
The original valve an "80" had failed so I replaced with a CV1708 as I coudn't find an 80 at sensible money online. I was advised the replacement is compatible with an 80....

The value of the output valve resistor measures correctly at around 400 Ohm.
richieyork is offline  
Old 17th Jun 2020, 3:06 pm   #20
richieyork
Pentode
 
richieyork's Avatar
 
Join Date: Dec 2010
Location: York, North Yorkshire, UK.
Posts: 212
Default Re: Sonora SF5 - Low HT

Quote:
Originally Posted by Station X View Post
Is the voltage selector correctly set?

What's the AC voltage on the HT secondary of the mains transformer?

Resistance of HT Choke/speaker energising coil?
Hi Paul
The voltage selector is set at 250v (originally was 220v as it originated from France).

AC voltage on each of the anodes on the CV1708 is 336v

Resistance of the speaker energising coil is 1.3k ohm

I've just noticed an earlier repair (not mine!) has used 16 + 16uf smoothing/filter cap can - the circuit shows 8 + 8 uf - would this account for the higher than expected voltage??

Cheers

Last edited by richieyork; 17th Jun 2020 at 3:16 pm. Reason: Noticed a wrong value component on the power supply?
richieyork is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 6:02 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.