Grundig Tuning Eye Help Needed - UK Vintage Radio Repair and Restoration Discussion Forum

Walston · 30th Mar 2013, 3:30 am

I am working on a Grundig Majestic 2056 (USA Version). The German version was Musikgerät Zauberklang 2065. The only schematic I have is in German. I have everything working except the tuning eye. The eye will light up, although it is dim. It barely moves with tuning. The control voltage is -1 to -18V according to the tube diagram. However the control voltage only changes from -0.5V to -0.8V based on my meter. I suspect a new tube may fix the brightness, but not the control voltage issue.

Any advice on where to look for the problem? This link should take you to the schematic. http://83.117.57.34/nvhr/Grundig_2065.pdf

Thanks for the help

ronbryan · 30th Mar 2013, 10:48 am

C37 (.047uF) might be leaky or R46 (2M2) might have gone high. These would be the first components to check.

The loading of your meter impedance could reduce the measured control voltage, as the circuit impedance is high - you may have to make an allowance for the loading, depending on your meter.

Ron

ukcol · 30th Mar 2013, 1:06 pm

The voltage to the control grid of the tuning eye will vary with signal strength of course. On AM this voltage is also use for AGC purposes.

Check this voltage on a strong AM signal. If the voltage is low because of a (say) leaky C37 then the AGC won't be effective and the IF amplifier will overload causing distortion. If on the other hand the voltage is low because the set is low gain then you won't get the symptoms associated with overloading.

Don't do this check on VHF/FM because clipping in the IF amplifier on a strong signal won't cause distortion; in fact the AGC is disabled by switch 9 in VHF/FM mode to provide AM rejection in the IF amplifier.

Colin

Footnote:

Not being familiar with the geography of Ohio I don't know what stations you can get. Perhaps you live in an area a long way away from any stations, in which case your received signals will be weak and the tuning eye won't move much anyway.

Walston · 30th Mar 2013, 2:57 pm

I have a EMUD 920 with a tuning eye and the local stations in both AM and FM are strong enough to close that tuning eye. I have been mostly working with FM, so I will do as you suggest on AM and see how it does.

On the meter impedance issue. I have a VTVM, if I remember correctly it has lower impedance, so I will try to measure the control voltage with it and see if the numbers are any different. Maybe it is just the Tube. I also am suspect of C37. I will change it out.

Walston · 30th Mar 2013, 5:16 pm

Obviously I meant higher impedance, not lower. DUH!

Walston · 1st Apr 2013, 3:11 pm

I checked the control voltage with my VTVM. Readings were about the same. -0.5 off station and -0.9V on a strong station. I received a NOS Eye tube in the mail, but it was DOA. The filament won't even light up. No conductivity across the filament. Very disappointing.

I have not had time to change C37 yet.

Walston · 2nd Apr 2013, 2:32 am

I checked R46, it showed 2.2Mohms on my meter. In fact if you trace back to pin 4 on EABC80, the voltage is the same there (-0.5V to -0.9V), so it seems low before the R46.

I don't have the right CAP to replace the C37. It is a .047 mF, 125 V. Closest I have is a .047 mF, 50V. So I will have to order some.

I rewired the magic eye tube socket for EM81. Seemed like a simple swap, I read it on the Radio Museum. The EM81 is much more available than EM85 and much cheaper. So I got a NOS EM81 and it is now nice and bright, but only moves slightly since I am still having the control voltage issues. So once I get the control voltage sorted out, it should be working good.

Any other ideas other than changing C37?

ukcol · 2nd Apr 2013, 9:41 am

It looks like the overall gain of your set is low, judging by the signal voltage measured at the detector. C37 won't be the culprit it that case.

If you can check the tubes by substitution that would be a good idea. Perhaps you could borrow the tubes from your EMUD 920 if it uses the same line up. Tube failure isn't necessarily the most likely cause but it is a quick thing to check if you have known good ones to hand.

If the tubes are OK check the tube voltages against those in the manual to see if anything is wrong there.

Another possibility is that the set is out of alignment, do the IF cores look like they have been disturbed?

Colin M

ronbryan · 2nd Apr 2013, 9:43 am

You could lift one leg of C37 and test its resistance on the highest resistance range of your multimeter, to confirm whether it is leaky or not. Temporarily replacing it with your 0.047 50V component would prove whether you are on the right lines. Normally the control voltage would be limited to a range of -1V to -20V approximately, so temporarily fitting an under-rated component (i.e. 50V rated) would do no harm.

Otherwise, looking for the cause of low IF gain would be the next step in the search for a larger control voltage. Check anode and screen grid voltages of the mixer and IF valve against the circuit diagram as the next step. Leaky decoupling capacitors can cause low gain by reducing screen grid voltage for example.

Ron

Walston · 3rd Apr 2013, 3:49 am

I swapped C37 and no change, so it is time to do an alignment. I have already swapped tubes and got no change. The grid voltages are similar to the schematic. The only voltage that seems to be off is the control voltage.

The only alignment procedure I have is in German, so if anyone has an alignment procedure for this unit in English, it would be GREATLY appreciated.

Thanks for all the help.

30th Mar 2013, 3:30 am	#1
Walston Retired Dormant Member Join Date: Mar 2013 Location: Marietta, Ohio, USA Posts: 9	Grundig Tuning Eye Help Needed I am working on a Grundig Majestic 2056 (USA Version). The German version was Musikgerät Zauberklang 2065. The only schematic I have is in German. I have everything working except the tuning eye. The eye will light up, although it is dim. It barely moves with tuning. The control voltage is -1 to -18V according to the tube diagram. However the control voltage only changes from -0.5V to -0.8V based on my meter. I suspect a new tube may fix the brightness, but not the control voltage issue. Any advice on where to look for the problem? This link should take you to the schematic. http://83.117.57.34/nvhr/Grundig_2065.pdf Thanks for the help

30th Mar 2013, 10:48 am	#2
ronbryan Octode Join Date: Jan 2003 Location: Guildford, Surrey, UK. Posts: 1,960	Re: Grundig Tuning Eye Help Needed C37 (.047uF) might be leaky or R46 (2M2) might have gone high. These would be the first components to check. The loading of your meter impedance could reduce the measured control voltage, as the circuit impedance is high - you may have to make an allowance for the loading, depending on your meter. Ron

30th Mar 2013, 1:06 pm	#3
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: Grundig Tuning Eye Help Needed The voltage to the control grid of the tuning eye will vary with signal strength of course. On AM this voltage is also use for AGC purposes. Check this voltage on a strong AM signal. If the voltage is low because of a (say) leaky C37 then the AGC won't be effective and the IF amplifier will overload causing distortion. If on the other hand the voltage is low because the set is low gain then you won't get the symptoms associated with overloading. Don't do this check on VHF/FM because clipping in the IF amplifier on a strong signal won't cause distortion; in fact the AGC is disabled by switch 9 in VHF/FM mode to provide AM rejection in the IF amplifier. Colin Footnote: Not being familiar with the geography of Ohio I don't know what stations you can get. Perhaps you live in an area a long way away from any stations, in which case your received signals will be weak and the tuning eye won't move much anyway. Last edited by ukcol; 30th Mar 2013 at 1:10 pm. Reason: Added footnote.

30th Mar 2013, 2:57 pm	#4
Walston Retired Dormant Member Join Date: Mar 2013 Location: Marietta, Ohio, USA Posts: 9	Re: Grundig Tuning Eye Help Needed I have a EMUD 920 with a tuning eye and the local stations in both AM and FM are strong enough to close that tuning eye. I have been mostly working with FM, so I will do as you suggest on AM and see how it does. On the meter impedance issue. I have a VTVM, if I remember correctly it has lower impedance, so I will try to measure the control voltage with it and see if the numbers are any different. Maybe it is just the Tube. I also am suspect of C37. I will change it out.

30th Mar 2013, 5:16 pm	#5
Walston Retired Dormant Member Join Date: Mar 2013 Location: Marietta, Ohio, USA Posts: 9	Re: Grundig Tuning Eye Help Needed Obviously I meant higher impedance, not lower. DUH!

1st Apr 2013, 3:11 pm	#6
Walston Retired Dormant Member Join Date: Mar 2013 Location: Marietta, Ohio, USA Posts: 9	Re: Grundig Tuning Eye Help Needed I checked the control voltage with my VTVM. Readings were about the same. -0.5 off station and -0.9V on a strong station. I received a NOS Eye tube in the mail, but it was DOA. The filament won't even light up. No conductivity across the filament. Very disappointing. I have not had time to change C37 yet.

2nd Apr 2013, 2:32 am	#7
Walston Retired Dormant Member Join Date: Mar 2013 Location: Marietta, Ohio, USA Posts: 9	Re: Grundig Tuning Eye Help Needed I checked R46, it showed 2.2Mohms on my meter. In fact if you trace back to pin 4 on EABC80, the voltage is the same there (-0.5V to -0.9V), so it seems low before the R46. I don't have the right CAP to replace the C37. It is a .047 mF, 125 V. Closest I have is a .047 mF, 50V. So I will have to order some. I rewired the magic eye tube socket for EM81. Seemed like a simple swap, I read it on the Radio Museum. The EM81 is much more available than EM85 and much cheaper. So I got a NOS EM81 and it is now nice and bright, but only moves slightly since I am still having the control voltage issues. So once I get the control voltage sorted out, it should be working good. Any other ideas other than changing C37? Last edited by Walston; 2nd Apr 2013 at 2:34 am. Reason: Clarification

2nd Apr 2013, 9:41 am	#8
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: Grundig Tuning Eye Help Needed It looks like the overall gain of your set is low, judging by the signal voltage measured at the detector. C37 won't be the culprit it that case. If you can check the tubes by substitution that would be a good idea. Perhaps you could borrow the tubes from your EMUD 920 if it uses the same line up. Tube failure isn't necessarily the most likely cause but it is a quick thing to check if you have known good ones to hand. If the tubes are OK check the tube voltages against those in the manual to see if anything is wrong there. Another possibility is that the set is out of alignment, do the IF cores look like they have been disturbed? Colin M

2nd Apr 2013, 9:43 am	#9
ronbryan Octode Join Date: Jan 2003 Location: Guildford, Surrey, UK. Posts: 1,960	Re: Grundig Tuning Eye Help Needed You could lift one leg of C37 and test its resistance on the highest resistance range of your multimeter, to confirm whether it is leaky or not. Temporarily replacing it with your 0.047 50V component would prove whether you are on the right lines. Normally the control voltage would be limited to a range of -1V to -20V approximately, so temporarily fitting an under-rated component (i.e. 50V rated) would do no harm. Otherwise, looking for the cause of low IF gain would be the next step in the search for a larger control voltage. Check anode and screen grid voltages of the mixer and IF valve against the circuit diagram as the next step. Leaky decoupling capacitors can cause low gain by reducing screen grid voltage for example. Ron

3rd Apr 2013, 3:49 am	#10
Walston Retired Dormant Member Join Date: Mar 2013 Location: Marietta, Ohio, USA Posts: 9	Re: Grundig Tuning Eye Help Needed I swapped C37 and no change, so it is time to do an alignment. I have already swapped tubes and got no change. The grid voltages are similar to the schematic. The only voltage that seems to be off is the control voltage. The only alignment procedure I have is in German, so if anyone has an alignment procedure for this unit in English, it would be GREATLY appreciated. Thanks for all the help.