Universal L-40 No Oscillator - UK Vintage Radio Repair and Restoration Discussion Forum

Christoffrad · 19th Feb 2023, 5:19 pm

This is a Universal L-40 110v AC/DC set. It also carries the name Altavoz on the rear cover.
The local oscillator on this set is not working. This was confirmed with a scope. however yesterday the oscillator did suddenly start and the set worked fine on MW. It also worked straight away this morning but after some attention to the loose dial cord it is again without an oscillator. Pins of the UCH42 have been cleaned and voltages look OK (HT and anode = 120v, Pin3 = 64v and pin 5=46v). An IF (470kHz) signal injected into RF input grid is amplified and audio detected fine.
The wavechange switch continuity seems ok so I suspect oscillator coil continuity. However this set is not covered by the Vintage Radio data stick and the circuit downloaded from the Radiomueum for the Lacora;Barcelona Universal L-40 is slightly different (eg shows fewer trimmers and associated Cs) and there is no layout so identification of the coil terminals is difficult.
Does anyone posess a more accurate circuit and a layout with coil terminal identification please.

Thanks

Christoffrad · 20th Feb 2023, 3:56 pm

Here are some related photos and the circuit from Radiomuseum which is not quite accurate.
BTW I should have mentioned that attaching an antenna results in noticeable audio pick up which confirms that the RF/IF/AF path is operating but only with the wavechange switch in the MW position. Also scoping the oscillator shows that it is inoperative. I think I need to be able to check out the coil positioned behind the wave change switch.
According to my searches there seem to be several interpretations of circuit for this set and the circuit provided by the Radiomuseum is just one of them!
So I'm keen to have one for my specific version.

Chris

Christoffrad · 21st Feb 2023, 4:19 pm

I have now traced out the actual oscillator circuit. See thumbnail.
As you will see, there aresome differences to the circuit provided by Radiomuseum.
The 60pf and 390pf capacitors have been checked and found to be within 5% of nominal value and the 4000pf is within 2%
As I also have a valve tester I suppose I should check the UCH42 as there's precious little left. Perhaps there's some deficiency in the wavechange switch?
Your comment would be most welcome and thanks to all who have viewed this thread.

C

Christoffrad · 21st Feb 2023, 5:16 pm

My appologies to Radiomuseum. Apparently we are not allowed to refer to their material.

Radio Tech · 21st Feb 2023, 8:36 pm

Suspect the voltages are dropping off, try checking the voltages around the HT and rectifier, there maybe even a defective solder joint around the first stage.

Ken

Station X · 23rd Feb 2023, 4:48 am

Quote:

Originally Posted by Christoffrad

My appologies to Radiomuseum. Apparently we are not allowed to refer to their material.

Yon can link to it, but please don't copy it and post it here.

Nickthedentist · 23rd Feb 2023, 10:27 am

What a neat and tidy underchassis layout. A complete contrast to a vaguely similar British Pilot set I’m currently working on.

Christoffrad · 23rd Feb 2023, 3:26 pm

Thank you or your responses.
In order to check the Cs mentioned above I had to unsolder one end of each of course. Having established they were all OK and soldering back I now find the set has worked perfectly (on both wavebands) for the last 3 days. Bizzare! Iwill keep monitoring and will bear suggestions in mind should the problem re-occur

C

19th Feb 2023, 5:19 pm	#1
Christoffrad Hexode Join Date: Jun 2018 Location: Cambridge, Cambridgeshire, UK. Posts: 262	Universal L-40 No Oscillator This is a Universal L-40 110v AC/DC set. It also carries the name Altavoz on the rear cover. The local oscillator on this set is not working. This was confirmed with a scope. however yesterday the oscillator did suddenly start and the set worked fine on MW. It also worked straight away this morning but after some attention to the loose dial cord it is again without an oscillator. Pins of the UCH42 have been cleaned and voltages look OK (HT and anode = 120v, Pin3 = 64v and pin 5=46v). An IF (470kHz) signal injected into RF input grid is amplified and audio detected fine. The wavechange switch continuity seems ok so I suspect oscillator coil continuity. However this set is not covered by the Vintage Radio data stick and the circuit downloaded from the Radiomueum for the Lacora;Barcelona Universal L-40 is slightly different (eg shows fewer trimmers and associated Cs) and there is no layout so identification of the coil terminals is difficult. Does anyone posess a more accurate circuit and a layout with coil terminal identification please. Thanks

20th Feb 2023, 3:56 pm	#2
Christoffrad Hexode Join Date: Jun 2018 Location: Cambridge, Cambridgeshire, UK. Posts: 262	Re: Universal L-40 No Oscillator Here are some related photos and the circuit from Radiomuseum which is not quite accurate. BTW I should have mentioned that attaching an antenna results in noticeable audio pick up which confirms that the RF/IF/AF path is operating but only with the wavechange switch in the MW position. Also scoping the oscillator shows that it is inoperative. I think I need to be able to check out the coil positioned behind the wave change switch. According to my searches there seem to be several interpretations of circuit for this set and the circuit provided by the Radiomuseum is just one of them! So I'm keen to have one for my specific version. Chris Attached Thumbnails Last edited by Cobaltblue; 21st Feb 2023 at 4:25 pm. Reason: Radiomuseum data removed

21st Feb 2023, 4:19 pm	#3
Christoffrad Hexode Join Date: Jun 2018 Location: Cambridge, Cambridgeshire, UK. Posts: 262	Re: Universal L-40 No Oscillator I have now traced out the actual oscillator circuit. See thumbnail. As you will see, there aresome differences to the circuit provided by Radiomuseum. The 60pf and 390pf capacitors have been checked and found to be within 5% of nominal value and the 4000pf is within 2% As I also have a valve tester I suppose I should check the UCH42 as there's precious little left. Perhaps there's some deficiency in the wavechange switch? Your comment would be most welcome and thanks to all who have viewed this thread. C Attached Thumbnails

21st Feb 2023, 5:16 pm	#4
Christoffrad Hexode Join Date: Jun 2018 Location: Cambridge, Cambridgeshire, UK. Posts: 262	Re: Universal L-40 No Oscillator My appologies to Radiomuseum. Apparently we are not allowed to refer to their material.

21st Feb 2023, 8:36 pm	#5
Radio Tech Nonode Join Date: Dec 2012 Location: Bocking, near Braintree, Essex, UK. Posts: 2,071	Re: Universal L-40 No Oscillator Suspect the voltages are dropping off, try checking the voltages around the HT and rectifier, there maybe even a defective solder joint around the first stage. Ken

23rd Feb 2023, 10:27 am	#7
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,846	Re: Universal L-40 No Oscillator What a neat and tidy underchassis layout. A complete contrast to a vaguely similar British Pilot set I’m currently working on.

23rd Feb 2023, 3:26 pm	#8
Christoffrad Hexode Join Date: Jun 2018 Location: Cambridge, Cambridgeshire, UK. Posts: 262	Re: Universal L-40 No Oscillator Thank you or your responses. In order to check the Cs mentioned above I had to unsolder one end of each of course. Having established they were all OK and soldering back I now find the set has worked perfectly (on both wavebands) for the last 3 days. Bizzare! Iwill keep monitoring and will bear suggestions in mind should the problem re-occur C