Nagra 3 power supply - UK Vintage Radio Repair and Restoration Discussion Forum

MikeCross · 31st Mar 2018, 12:42 pm

Hi,
I am looking for help to service my Nagra 3 power supply.
I used the recorder last summer to record some traction engines and on replaying the tape, parts had a buzzing/ clicking noise which went away after a number of minutes. I guess the unit contains the usual transformer/rectifiers and capacitors but before I do something wrong I would like to know the circuitry and any tricks that might need to be known before opening the metal case.

I have used this machine for man years and I think it is due some TLC.

Many Thanks
Mike

jamesperrett · 31st Mar 2018, 6:49 pm

Have you eliminated other potential sources of interference like someone using a mobile phone nearby? Have you tried recording on it more recently and is the problem still there?

barretter · 31st Mar 2018, 8:50 pm

The Nagra 3 doesn't have an internal power supply. It runs off either 12 D cells or an external supply connected via a 6-pin Kuchel plug ( a higher class lockable DIN plug). Is that what you mean? If so you could check the recorder by installing 12 new D cells which would eliminate any effect of a malfunctioning external supply.
There is an internal voltage stabilizer circuit so that might be at fault, but I have yet to find a readable circuit diagram. You can find a maintenance manual on the internet by googling Nagra 3. There is a CD-ROM of Nagra documents currently on the well-known auction website for £5-6.

barretter · 31st Mar 2018, 10:00 pm

That should have been Tuchel plug. The internal voltage stabiliser (or "tension" stabiliser) is contained in a screened can inside the Nagra but there doesn't seem to be any easy way of removing it and, in any case, it probably contains germanium transistors which it would be difficult to find viable replacements for.

TowerRadio · 31st Mar 2018, 11:52 pm

Might it be noise from a brushed motor (if the recorder has one)?

dseymo1 · 1st Apr 2018, 10:38 am

If it turns out to be the external PSU, aftermarket replacements are available at a reasonable price.

barretter · 1st Apr 2018, 11:08 am

The external power supply is just a simple combination of mains transformer, diode bridge and electrolytic smoothing capacitor with no regulation (which is done inside the machine) so it shouldn't be too hard to fix. Any DC voltage between 15V to 30V is acceptable.

MikeCross · 3rd Apr 2018, 4:41 pm

Thank you all for your help.
External power supply rebuilt with new caps and all is fine.

31st Mar 2018, 12:42 pm	#1
MikeCross Tetrode Join Date: Sep 2016 Location: Tring, Hertfordshire, UK. Posts: 87	Nagra 3 power supply Hi, I am looking for help to service my Nagra 3 power supply. I used the recorder last summer to record some traction engines and on replaying the tape, parts had a buzzing/ clicking noise which went away after a number of minutes. I guess the unit contains the usual transformer/rectifiers and capacitors but before I do something wrong I would like to know the circuitry and any tricks that might need to be known before opening the metal case. I have used this machine for man years and I think it is due some TLC. Many Thanks Mike

31st Mar 2018, 6:49 pm	#2
jamesperrett Octode Join Date: May 2007 Location: Liss, Hampshire, UK. Posts: 1,873	Re: Nagra 3 power supply Have you eliminated other potential sources of interference like someone using a mobile phone nearby? Have you tried recording on it more recently and is the problem still there?

31st Mar 2018, 8:50 pm	#3
barretter Heptode Join Date: Jan 2006 Location: Todmorden, West Yorkshire, UK. Posts: 870	Re: Nagra 3 power supply The Nagra 3 doesn't have an internal power supply. It runs off either 12 D cells or an external supply connected via a 6-pin Kuchel plug ( a higher class lockable DIN plug). Is that what you mean? If so you could check the recorder by installing 12 new D cells which would eliminate any effect of a malfunctioning external supply. There is an internal voltage stabilizer circuit so that might be at fault, but I have yet to find a readable circuit diagram. You can find a maintenance manual on the internet by googling Nagra 3. There is a CD-ROM of Nagra documents currently on the well-known auction website for £5-6.

31st Mar 2018, 10:00 pm	#4
barretter Heptode Join Date: Jan 2006 Location: Todmorden, West Yorkshire, UK. Posts: 870	Re: Nagra 3 power supply That should have been Tuchel plug. The internal voltage stabiliser (or "tension" stabiliser) is contained in a screened can inside the Nagra but there doesn't seem to be any easy way of removing it and, in any case, it probably contains germanium transistors which it would be difficult to find viable replacements for. Attached Thumbnails

31st Mar 2018, 11:52 pm	#5
TowerRadio Hexode Join Date: Mar 2008 Location: Bristol, UK. Posts: 388	Re: Nagra 3 power supply Might it be noise from a brushed motor (if the recorder has one)?

1st Apr 2018, 10:38 am	#6
dseymo1 Retired Dormant Member Join Date: Dec 2007 Location: Shropshire, UK. Posts: 3,051	Re: Nagra 3 power supply If it turns out to be the external PSU, aftermarket replacements are available at a reasonable price.

1st Apr 2018, 11:08 am	#7
barretter Heptode Join Date: Jan 2006 Location: Todmorden, West Yorkshire, UK. Posts: 870	Re: Nagra 3 power supply The external power supply is just a simple combination of mains transformer, diode bridge and electrolytic smoothing capacitor with no regulation (which is done inside the machine) so it shouldn't be too hard to fix. Any DC voltage between 15V to 30V is acceptable.

3rd Apr 2018, 4:41 pm	#8
MikeCross Tetrode Join Date: Sep 2016 Location: Tring, Hertfordshire, UK. Posts: 87	Re: Nagra 3 power supply Thank you all for your help. External power supply rebuilt with new caps and all is fine.