Grundig 2035W/3D Tuning Indicator

[Peter J Ward]

Good Morning. I'm pleased to join your forum as a complete novice so please bear with me whilst I get to know the etiquette.
I am restoring the old family radio and at the moment struggling to get a decent deflection on the tuning indicator EM80. From the valve specification I am expecting a variation between 0 and -15V on the grid, but on a good FM signal (excellent volume, low noise) I'm only measuring about -1.5V, and the deflection on the valve is minimal. (AM signal produces less but I think I have an issue in an earlier stage.) Does anyone have an idea of what voltage would be reasonable to expect.

[ms660]

According to the schematic I'm looking at the tuning indicator is shown as a EM85.

Lawrence.

[agardiner]

These sets were found with EM80 and EM85 indicators. I have even come across an original EM84 in one.

Have you replaced all the old capacitors in the radio? A leaky one could easily prevent the indicator from working correctly.

[Gabe001]

This is a common issue and there are quite a few threads.

Common culprits include leaky capacitors, resistors in the environs of the tuning indicator gone high, a weak front end valve (commonly ecc85, I haven't seen a schematic for this model), the FM discriminator (upside down) electrolytic being leaky and aerial/reception issues beyond your control

[Silicon]

Another issue to be aware of is that tuning indicators are often controlled by the voltage on the AGC line.

The AGC circuit usually has a high resistance and so the voltmeter must have a high input resistance to avoid getting a misleading reading.

Does your voltmeter have an input resistance of 10MegOhms or greater?

[Peter J Ward]

Thank you all for your responses.

Regarding the circuit diagram, I have been unable to find the exact schematic for this particular model, those available on the web do not have Short Wave but this model does.
Interestingly the rear chassis cover which names all the valves, shows an EM81 rather than the EM80 fitted, although this may have been changed at some stage.

I've checked the capacitors and resistors with an LCR meter around the discriminator stage and tuning indicator and they all measure as expected.

The suggestion of a weak front end valve is a good one but AM signals also do not deflect the indicator sufficiently, which could point to the mixer valve ECH81 to where the AGC returns so thanks for that idea, I will pursue it further.

[agardiner]

The EM80 & EM81 are pretty interchangeable. I would certainly try a replacement ECH81 as the next step.

[roffe]

This version has EM80 and SW.
https://www.radiomuseum.org/r/grundi...dgb.html#forum

[Ed_Dinning]

Hi Peter, be aware that these digital LCR meters do not always read accurately if the caps are leaking.

Ed