EMUD 920 Restoration / rejuvenation - UK Vintage Radio Repair and Restoration Discussion Forum

Walston · 20th Mar 2013, 2:10 am

Hi guys, greeting from the US. I posted this on the US sites and the guys there recommended I ask you guys since the set I am working on is a European set and they had limited knowledge. I have a EMUD 920. It has a radio with AM/FM/SW and it has a Monarch Phono. It is actually a very nice set and after some work I have everything working quite well except one thing. The radio plays very well in AM/FM and SW but anytime when I push the "stereo" button, the right speaker goes out. The same happens when I use the phono. Plays great through all speakers in mono, but when I push the stereo button, the right side goes out.

On the schematic when the switch is pushed to "stereo" it energizes the stereo circuit. That all seems to be working and as far as I can tell the switch is making good contact. I cleaned it with de Toxit. The volume pot is a two part and with the second part controlling the stereo circuit when energized. You could pull out on the volume controller and then you can turn the two pots separately. I assume that was how you balanced the speakers. The stereo pot currently makes no difference at all whether the stereo button is pushed or not. I did check the resistance of the stereo pot and it seems to be performing as designed, that is it is not dirty.

The unit is unmolested (never been worked on), but there seems to be a couple differences from the schematic. The schematic is for EMUD 920 and 921.

So my question is the: Were there units built by EMUD that had the "stereo" button but were not actually set up to play in stereo. Was it an option so to speak? Was that the difference between 920 or 921? I just feel like I have been trying to find a problem that is not there because the unit was not originally set up to play stereo, but I have been unable to confirm that.

Any knowledge or ideas would be much appreciated.

Herald1360 · 20th Mar 2013, 1:56 pm

It looks like the EMUD920 is a US Export version of the German EMUD Superb 61. There's some information in Radiomuseum for the 61.

Also found this:

https://www.samswebsite.com/en/photo...index/id/49300

Which looks promising for the US 920 but costs $15.

From what can be seen of the thumbnail schematic in RM, it looks like there should be two single ended EL84 audio outputs, but whether anything really complex for the stereo/mono switching happens can't be seen. ISTR some of the wilder excesses either paralleled or even push pull connected the output tubes for mono which could result in some strange switching problems.

Of course many early stereo radiograms were only stereo for the record side unless an (expensive) optional stereo decoder was specified for the FM radio.

Edit: Read your post a bit better- it seems you have the schematic. Since it's not available in the forum reference perhaps you could scan and post here for us to cogitate over?

MotorBikeLes · 21st Mar 2013, 7:04 pm

I know nothing about this set, but the NordMende stereo sets from the early '60s had a DIN socket (5 way?) on the back. This either had a dummy plug if the model was supplied without a stereo decoder, or if fitted, the stereo decoder was plugged there instead.
Do you have an empty such socket anywhere? Worth checking on.
Les.

Walston · 22nd Mar 2013, 2:26 am

Here is the schematic. It is 3 pages, but I overlapped them so I think it is all there. Maybe this may give you guys an idea or two. The only thing that I have found odd so far is resistor 39, located near the stereo switch 11/27 to 12/28 is not there, at least I cannot find it. This is what started me thinking that maybe this thing was set up different. The schematic is for a 920 and a 921 and I have not been able to determine the difference. Mine is a 920.

I have the rest of the Sams and can post if you think it would help.

I am fairly new at this, so maybe I am missing something obvious and hopefully you more experience guys can help.

MotorBikeLes, the only input plug on the back is for a Tape input. There is a test port and external speaker connections. These speakers behave the same way. That is the right channel goes out if I push the stereo switch.

Thanks for the help.

ronbryan · 22nd Mar 2013, 12:14 pm

As Herald says, It's push-pull in mono and single ended in stereo.

I would switch to stereo and firstly check to see if V7 anode (plate) has any volts on it. It could be that T3 has an open circuit primary.

Ron

Walston · 24th Mar 2013, 4:26 am

Well I think I have this mystery solved. After some more detailed studying of the schematic, looks like only the phono and tape go to the stereo button hookup. I had to order some parts for the phono so I couldn't test it. The tape is just an input plug, so I rigged up a stereo input and sure enough it played perfect through both speakers with the stereo button pushed!

20th Mar 2013, 2:10 am	#1
Walston Retired Dormant Member Join Date: Mar 2013 Location: Marietta, Ohio, USA Posts: 9	EMUD 920 Restoration / rejuvenation Hi guys, greeting from the US. I posted this on the US sites and the guys there recommended I ask you guys since the set I am working on is a European set and they had limited knowledge. I have a EMUD 920. It has a radio with AM/FM/SW and it has a Monarch Phono. It is actually a very nice set and after some work I have everything working quite well except one thing. The radio plays very well in AM/FM and SW but anytime when I push the "stereo" button, the right speaker goes out. The same happens when I use the phono. Plays great through all speakers in mono, but when I push the stereo button, the right side goes out. On the schematic when the switch is pushed to "stereo" it energizes the stereo circuit. That all seems to be working and as far as I can tell the switch is making good contact. I cleaned it with de Toxit. The volume pot is a two part and with the second part controlling the stereo circuit when energized. You could pull out on the volume controller and then you can turn the two pots separately. I assume that was how you balanced the speakers. The stereo pot currently makes no difference at all whether the stereo button is pushed or not. I did check the resistance of the stereo pot and it seems to be performing as designed, that is it is not dirty. The unit is unmolested (never been worked on), but there seems to be a couple differences from the schematic. The schematic is for EMUD 920 and 921. So my question is the: Were there units built by EMUD that had the "stereo" button but were not actually set up to play in stereo. Was it an option so to speak? Was that the difference between 920 or 921? I just feel like I have been trying to find a problem that is not there because the unit was not originally set up to play stereo, but I have been unable to confirm that. Any knowledge or ideas would be much appreciated.

20th Mar 2013, 1:56 pm	#2
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: EMUD 920 Restoration / Rejuvination It looks like the EMUD920 is a US Export version of the German EMUD Superb 61. There's some information in Radiomuseum for the 61. Also found this: https://www.samswebsite.com/en/photo...index/id/49300 Which looks promising for the US 920 but costs $15. From what can be seen of the thumbnail schematic in RM, it looks like there should be two single ended EL84 audio outputs, but whether anything really complex for the stereo/mono switching happens can't be seen. ISTR some of the wilder excesses either paralleled or even push pull connected the output tubes for mono which could result in some strange switching problems. Of course many early stereo radiograms were only stereo for the record side unless an (expensive) optional stereo decoder was specified for the FM radio. Edit: Read your post a bit better- it seems you have the schematic. Since it's not available in the forum reference perhaps you could scan and post here for us to cogitate over? __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

21st Mar 2013, 7:04 pm	#3
MotorBikeLes Nonode Join Date: Dec 2012 Location: Kirk Michael, Isle of Man Posts: 2,350	Re: EMUD 920 Restoration / rejuvenation I know nothing about this set, but the NordMende stereo sets from the early '60s had a DIN socket (5 way?) on the back. This either had a dummy plug if the model was supplied without a stereo decoder, or if fitted, the stereo decoder was plugged there instead. Do you have an empty such socket anywhere? Worth checking on. Les.

22nd Mar 2013, 12:14 pm	#5
ronbryan Octode Join Date: Jan 2003 Location: Guildford, Surrey, UK. Posts: 1,960	Re: EMUD 920 Restoration / rejuvenation As Herald says, It's push-pull in mono and single ended in stereo. I would switch to stereo and firstly check to see if V7 anode (plate) has any volts on it. It could be that T3 has an open circuit primary. Ron

24th Mar 2013, 4:26 am	#6
Walston Retired Dormant Member Join Date: Mar 2013 Location: Marietta, Ohio, USA Posts: 9	Re: EMUD 920 Restoration / rejuvenation Well I think I have this mystery solved. After some more detailed studying of the schematic, looks like only the phono and tape go to the stereo button hookup. I had to order some parts for the phono so I couldn't test it. The tape is just an input plug, so I rigged up a stereo input and sure enough it played perfect through both speakers with the stereo button pushed!