Trying to get my EM85 Eye Tube working

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Trying to get my EM85 Eye Tube working

Post by Walston on Sat Mar 30, 2013 8:35 am

I am working on a Grundig Majestic 2065 (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, and that kind of makes sense since the tuning eye does move ever so slightly with tuning. 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, although it is in German. http://83.117.57.34/nvhr/Grundig_2065.pdf

Thanks for the help

Walston
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Re: Trying to get my EM85 Eye Tube working

Post by Resistance is Futile on Sat Mar 30, 2013 12:58 pm

Since the voltage is the issue then look around the AVG circuit. If the voltage is too low then look for a capacitor that is either not passing a signal (open cap) or loading the signal down, (Shorting cap). There is also the biasing section of the tube (the grid) and it controls the plate current. If the resistance of the control grid is too high it will not allow the eye-tube to be as sensitive as needed. That is a major defect in old resistors climbing in value. I am not that familiar with the tube # designation to distinguish which is the eye-tube.

This is strictly a guess as to the eye-tube EM85, check the 470Kohm on the plate, R46 2.2Meg ohm and C42 70 pf.

The Model Musikgerät Zauberklang from my understanding means Music Magic.
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Re: Trying to get my EM85 Eye Tube working

Post by Walston on Mon Apr 01, 2013 11:19 am

Thanks for the ideas for places to look. I checked the control voltage with my VTVM to make sure the impedance of my digital meter was not impacting the readings. Unfortunately not, they were about the same -0.5V off station and -0.9V on a strong station. I received a NOS tube in the mail, but it was DOA, the filament is gone, won't light up and no conductivity it at all. Very disappointing.

I am going to rewire the socket for a EM81, they are much more available and from reading on the Radio Museum it sounds like a simple swap.

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Re: Trying to get my EM85 Eye Tube working

Post by Walston on Mon Apr 01, 2013 11:21 am

I have not had time to swap C37 yet, I suspect it may be leaking. The 470Kohm resister you mention is right on. I still have to check the other ones.

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Re: Trying to get my EM85 Eye Tube working

Post by Walston on Mon Apr 01, 2013 10:36 pm

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.

Unfortunately I have not located C42 yet. I will keep looking.

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 and C42?

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Re: Trying to get my EM85 Eye Tube working

Post by NashvilleRad on Wed Apr 03, 2013 12:08 pm

I have a Graetz that is very similar to your set (that I've posted about before). I got it for $10 and replaced a fuse and a short wire run and it works great - with the exception of the eye tube - someone disconnected the eye tube power connections to the tube mount, and the EM80 is missing - I suspect people 'robbed' eye tubes from these sets since they can be pricey.

I have let this set sit because I haven't chased down an EM80, plus, the closest schematic I have been able to find is a Comedia analogue based on tube & transformer lineup, and the associated components in the eye tube circuit.

I may drag it back out in the next day or so to share in the pursuit of getting the eye tube functional, and will keep track of this post for sure.

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Re: Trying to get my EM85 Eye Tube working

Post by Walston on Wed Apr 03, 2013 6:27 pm

I replaced the C37 and that made no change. C42 is a small pF plastic capacitor and I kind of doubt is leaking. But I will try to get it replaced if possible. It may be inside a can and very difficult to get to, the schematic doesn't show that, but I still have not found it.

I am starting to think that maybe it is an alignment issue.

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Re: Trying to get my EM85 Eye Tube working

Post by Walston on Wed Apr 03, 2013 6:28 pm

If the unit is out of alignment would that cause a weak control voltage to the tuning eye?

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Re: Trying to get my EM85 Eye Tube working

Post by Bill Cahill on Wed Apr 03, 2013 7:01 pm

If you are getting strong stations I would say alignment isn't your prolbem.
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Re: Trying to get my EM85 Eye Tube working

Post by Walston on Wed Apr 03, 2013 9:12 pm

Bill Cahill wrote:If you are getting strong stations I would say alignment isn't your prolbem.
Bill Cahill

That could very well be true. Do you have a suggestion on what else to look at?

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