FM tuner and IF adjustment on '55 Minerva - UK Vintage Radio Repair and Restoration Discussion Forum

Richard_66 · 8th Jul 2007, 6:50 pm

hi,

I am new here, so may I introduce myself shortly: I am living in Austria, have some knowledge of elctronics (but little expericence with valves) and currently I am trying to bring a little collection of three "Minerva" radios to live.
Minerva is a former Austrian radio manufacturer (see a little history on http://www.minervaradio.com )

These radios are from around 1955. The biggest one is named 'Consul', a fat one with five loudspeakers and even two short wave bands, the mid one is 'Record W', the smallest 'Minx'.

All three are running well meanwhile. However, I would like to improve FM reception at least for the two bigger ones. Currently it is quite hard to tune them for satisfyingly clear sound.

I have an 'Eumig 3D' (another Austrian manufacturer) from 1960 with very similar circuitry, which shows how good and stable the reception might be.

On the 'Record' I already dared to fiddle with the numerous screws on tuner and IF filter. Now at least there is only one maximum per station on the magic eye, and this maximum corresponds with the point of clearest reception (before there were two maxima of different height, and the point of lowest distortions somewhere inbetween). Also the IF signal, checked on an osccilloscpe at the output of the IF, shows only minimal remaining residual AM when the radio is tuned to maximum voltage at the ratio detector.

However, I was unhappy to see that for some of the screws, I could not observe any effect when turning them, so I moved them back to their original position as good as I could remember, but of course with a bad feeling about it ...

Below, I posted (besides some pics of the 'Consul'), after quite some cleaning), a wiring diagram of the Consul, a picture of the tuner and one of the IF filter. These devices are identical on the Consul and on the Record. The IF filter has "480kHz" stamped on it, but this is obviously erroneous.

Does someone of you (hopefully) recognize the tuner or IF filter, and can help me identify the different screws? Probably these components are equal in other manufacturers' radios of that era?

Is it at all possible to do such an adjustment with some good stations to receive, and an oscilloscope only?

best regards,
Richard

Richard_66 · 8th Jul 2007, 7:39 pm

I forgot to attach the wiring diagram I mentioned in the text - perhaps could you please add it to my posting (perhaps replacing the first photo)? If not easily possible, I will post it later in a reply.

best regards,
Richard ( richard.hirn@aon.at )

Steve_P · 8th Jul 2007, 9:40 pm

Well... firstly, you can align the RF but not the IF this way. In fact, the IF's were probably OK, and you should leave alignment alone until you have searched for faults.

On FM, the IF is more than likely 10.7 Mhz. On AM, it is usually around the 470 Khz mark, in your case 480 Khz at a guess. Not all the happy little screws in the set will be operative on every waveband, and the ones that did nothing on FM were AM ones. 480 Khz was not a mistake!

The IF may sound OK, but it may be off frequency now. So you now need a Signal Generator and a Scope to put it back. And the A.M. too!

Change any suspect caps, and although not IF/RF related, change the cap on the Anode of the EABC80 - Marked up 50n on your diagram, a 0.047uF will be the nearest.

Never have a go at a radio by realigning first, unless somebody else has been there first and the IF's seem to be off.

The VHF side is done with the ECC85. They don't often go wrong, apart from the valve itself. And they need a good aerial...

The ECH81 works as a Frequency Changer at AM and an IF amp at FM. The EF85 as an IF amp on all bands. The UABC80 acts as a Diode on AM, An FM Demod on FM and a Triode on all bands. (AF.)

The wavechange switch (they often need a clean!) switches various trimmers in or out as well as switching the FM or AM in depending on where it is set.

Cheers,

Steve P

Richard_66 · 9th Jul 2007, 6:27 am

Steve,
Thanks a lot for this quick answer!

To my "defense", I must say that there is a dedicated IF filter part for the AM bands (which I did not touch), and I have seen a clear signal around 10MHz (judged which the oscilloscope) at the terminals of the IF filter I mentioned above. I will check again if there is any 480kHz, too, on this filter, but I doubt it.

So I will see for the caps as you suggested, and then try to borrow myself a signal generator, and see if the IF frequency is off.

Any further suggestions concerning the meaning of the screws will be welcome!

best regards,
Richard

Steve_P · 9th Jul 2007, 1:17 pm

Well first, Read and Learn...

http://www.vintage-radio.com/repair-...rf-stages.html

And they are called trimmers, not screws. I hope you're using a proper trimmer tool rather than just a screwdriver...

Cheers,

Steve P

Richard_66 · 9th Jul 2007, 9:43 pm

Steve,
thanks again! Perhaps I was sounding too green, but I admit reading through these well-written basics wont hurt and there is a lot for me to learn. And probably the section about widening and flattening the response of the IF filters is very applicable to these radio sets - I learnt from a previous owner that they actually never played well on FM. E.g. the "s"s of the news speaker (peak modulation) never came through well.

Meanswhile, I also got hold of a fine signal generator. Might take some days till I find the time to bring it here and play with it ...

best regards,
Richard

P.S. dont worry, I got a matching tool with a non-conductive blade for turning the trimmers.

P.P.S. I have seen they are secured partially with a drop of wax, partially with paint. What is the material you would recommend for re - securing them?

Brian R Pateman · 9th Jul 2007, 10:00 pm

For the ultimate professional approach use "Loctite."

From a practical point of view I use up my wife's old nail varnish - cheap and such pretty colours!

Regards,

Richard_66 · 26th Jul 2007, 1:22 am

hi,
first, thanks alot to Steve and Brian for their valuable hints!

It really took me some time now (why can't women share our passion for old radios?). I borrowed a signal generator and a good oscilloscope. Of course, Steve had been right and I had inadverdently misaligned the IF both on FM and AM on one of the Minerva's. However, meanwhile I managed to restore the alignment.

For alignment of the FM IF, I put all IF stages to the same resonance frequency (i.e. 10.7MHz). A slight difference in resonance frequency would make the frequency response look better (i.e. with a flat top), but the radio would not sound better and the magic eye would be misleading.

The frequency response of the IF filters is shown in the first picture. The signal generator was sweeping from 10.3 to 11.1MHz. The oscilloscope shows an inverted and a bit funny 'envelope' curve, but I think one can conclude how the frequency response actually looks like.

Then I tried the hints for widening and flattening the frequency response of the IF section, as proposed in the link that Steve posted above. With 27kOhms across the capacitors of both filter stages, the frequency response looked like in picture 2 (same frequency span of course, but higher gain). So the curve is much wider ( I think this is actually too much, I will use larger resistors eventually).

However, I did not succeed so far in making the range of the ratio detector wider. The radio already sounds much cleaner, but is still difficult to tune and reacts unpleasantly to any thermal drift. The response of the ratio detector is shown in the third picture (same frequency span). Its's linear range is just around +/- 100kHz.

Would you recommend to try to modify the ratio detector? I have posted a circuit diagram above, could you please give me a hint where to start?

thanks in advance, and best regards,
Richard

Steve_P · 26th Jul 2007, 7:26 pm

I can't quite see what is what on your circuit diagram so I'm winging a bit here, but that's part of the fun.

There's an Electrolytic, Looks like 32uF. Across this is a smaller cap, 4nF and a resistor 47K. Change the electrolytic and the others if need be. Then, set it up.

You'll find the way to do this on this page:

http://www.vintage-radio.com/repair-...alignment.html

It's under IF Alignment.

Cheers,

Steve P

Richard_66 · 26th Jul 2007, 10:35 pm

Thanks, Steve!
The electrolytic (originally 3.2uF) is already a new one! The smaller cap is a ceramic one ( cannot test it, but it is unlikely to fail) and the resistor is ok.

The ratio detector circuit is already centered correctly. I have the impression that the set is already working as Mother Nature intended it to do, but it cannot cope with the higher modulation depth of current radio stations.

So I was looking for a way to change the ratio detector in order to get a wider linear range (e.g. +/- 150kHz instead of +/- 100kHz).

best regards,
Richard

Richard_66 · 29th Jul 2007, 3:34 am

hi,

I just had another 'session' on my victim. Success, what concerns the ratio detector: A quite small resistor (just 10kOhms this time) across the final IF transformer (which actually builds the ratio detector) did the trick. Not a very glorious finding, as the measure was in line with the instructions in http://www.vintage-radio.com/repair-...rf-stages.html).

The attached pics show the demodulated signal without and then with dampening (in both cases sweeping from 10.3 to 11.1MHz, but different gain). In the latter picture, the slope of the ratio detector's output is reduced, and the linear range is extended, Seems the reception has become audibly clearer since then.

What unfortunately remains: I also noticed that the preselection in the tuner section is quite narrow. However I am not very motivated to touch the tuner ...

best regards,
Richard

PWH · 29th Jul 2007, 9:24 am

If you have another ecc85 in a set which gives good reception swap it and see.

ECC85's go low emission. I have had sets with no FM. Changing the ECC85 restored it perfectly

Richard_66 · 29th Jul 2007, 11:04 pm

Thanks for the hint, PWH!

I have swapped the ECC85 against a well-working, newer piece. However it would not get better. Seems that this particular tuner (of the Minerva Record) has its limits. Anyhow, the FM reception has much improved already.

I have now also tried the same procedure - IF broadening and adjustment, together with shifting the FM oscillator and preselection up 4MHz, to get my favourite station - on the large set (Minerva Consul). This time I was rewarded with perfect sound (out of five loudspeakers, many new caps and a complete set of new valves).

For the 'Record', there is obviously still some room for improvement - but probably I was just expecting too much ...

best regards,
Richard

Steve_P · 29th Jul 2007, 11:17 pm

This is probably the case. FM is more crowded now and a lot more processing is used. Some of the early FM units did have their limits, and the transmissions now can drift about more before something is done about them.

In years gone by, the Readings and Measurements were taken at least once a day. Not now though.

I'll stop there - as some on this forum know, the downhill slide of Transmission is a constant gripe of mine.

Who shouted 'One of Many'...

Cheers,

Steve P

8th Jul 2007, 6:50 pm	#1
Richard_66 Retired Dormant Member Join Date: May 2007 Location: Vienna, Austria Posts: 9	FM tuner and IF adjustment on '55 Minerva hi, I am new here, so may I introduce myself shortly: I am living in Austria, have some knowledge of elctronics (but little expericence with valves) and currently I am trying to bring a little collection of three "Minerva" radios to live. Minerva is a former Austrian radio manufacturer (see a little history on http://www.minervaradio.com ) These radios are from around 1955. The biggest one is named 'Consul', a fat one with five loudspeakers and even two short wave bands, the mid one is 'Record W', the smallest 'Minx'. All three are running well meanwhile. However, I would like to improve FM reception at least for the two bigger ones. Currently it is quite hard to tune them for satisfyingly clear sound. I have an 'Eumig 3D' (another Austrian manufacturer) from 1960 with very similar circuitry, which shows how good and stable the reception might be. On the 'Record' I already dared to fiddle with the numerous screws on tuner and IF filter. Now at least there is only one maximum per station on the magic eye, and this maximum corresponds with the point of clearest reception (before there were two maxima of different height, and the point of lowest distortions somewhere inbetween). Also the IF signal, checked on an osccilloscpe at the output of the IF, shows only minimal remaining residual AM when the radio is tuned to maximum voltage at the ratio detector. However, I was unhappy to see that for some of the screws, I could not observe any effect when turning them, so I moved them back to their original position as good as I could remember, but of course with a bad feeling about it ... Below, I posted (besides some pics of the 'Consul'), after quite some cleaning), a wiring diagram of the Consul, a picture of the tuner and one of the IF filter. These devices are identical on the Consul and on the Record. The IF filter has "480kHz" stamped on it, but this is obviously erroneous. Does someone of you (hopefully) recognize the tuner or IF filter, and can help me identify the different screws? Probably these components are equal in other manufacturers' radios of that era? Is it at all possible to do such an adjustment with some good stations to receive, and an oscilloscope only? best regards, Richard Attached Thumbnails

8th Jul 2007, 7:39 pm	#2
Richard_66 Retired Dormant Member Join Date: May 2007 Location: Vienna, Austria Posts: 9	FM tuner and IF adjustment on '55 Minerva I forgot to attach the wiring diagram I mentioned in the text - perhaps could you please add it to my posting (perhaps replacing the first photo)? If not easily possible, I will post it later in a reply. best regards, Richard ( richard.hirn@aon.at ) Attached Thumbnails

8th Jul 2007, 9:40 pm	#3
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: FM tuner and IF adjustment on '55 Minerva Well... firstly, you can align the RF but not the IF this way. In fact, the IF's were probably OK, and you should leave alignment alone until you have searched for faults. On FM, the IF is more than likely 10.7 Mhz. On AM, it is usually around the 470 Khz mark, in your case 480 Khz at a guess. Not all the happy little screws in the set will be operative on every waveband, and the ones that did nothing on FM were AM ones. 480 Khz was not a mistake! The IF may sound OK, but it may be off frequency now. So you now need a Signal Generator and a Scope to put it back. And the A.M. too! Change any suspect caps, and although not IF/RF related, change the cap on the Anode of the EABC80 - Marked up 50n on your diagram, a 0.047uF will be the nearest. Never have a go at a radio by realigning first, unless somebody else has been there first and the IF's seem to be off. The VHF side is done with the ECC85. They don't often go wrong, apart from the valve itself. And they need a good aerial... The ECH81 works as a Frequency Changer at AM and an IF amp at FM. The EF85 as an IF amp on all bands. The UABC80 acts as a Diode on AM, An FM Demod on FM and a Triode on all bands. (AF.) The wavechange switch (they often need a clean!) switches various trimmers in or out as well as switching the FM or AM in depending on where it is set. Cheers, Steve P __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

9th Jul 2007, 6:27 am	#4
Richard_66 Retired Dormant Member Join Date: May 2007 Location: Vienna, Austria Posts: 9	Re: FM tuner and IF adjustment on '55 Minerva Steve, Thanks a lot for this quick answer! To my "defense", I must say that there is a dedicated IF filter part for the AM bands (which I did not touch), and I have seen a clear signal around 10MHz (judged which the oscilloscope) at the terminals of the IF filter I mentioned above. I will check again if there is any 480kHz, too, on this filter, but I doubt it. So I will see for the caps as you suggested, and then try to borrow myself a signal generator, and see if the IF frequency is off. Any further suggestions concerning the meaning of the screws will be welcome! best regards, Richard

9th Jul 2007, 1:17 pm	#5
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: FM tuner and IF adjustment on '55 Minerva Well first, Read and Learn... http://www.vintage-radio.com/repair-...rf-stages.html And they are called trimmers, not screws. I hope you're using a proper trimmer tool rather than just a screwdriver... Cheers, Steve P __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

9th Jul 2007, 9:43 pm	#6
Richard_66 Retired Dormant Member Join Date: May 2007 Location: Vienna, Austria Posts: 9	Re: FM tuner and IF adjustment on '55 Minerva Steve, thanks again! Perhaps I was sounding too green, but I admit reading through these well-written basics wont hurt and there is a lot for me to learn. And probably the section about widening and flattening the response of the IF filters is very applicable to these radio sets - I learnt from a previous owner that they actually never played well on FM. E.g. the "s"s of the news speaker (peak modulation) never came through well. Meanswhile, I also got hold of a fine signal generator. Might take some days till I find the time to bring it here and play with it ... best regards, Richard P.S. dont worry, I got a matching tool with a non-conductive blade for turning the trimmers. P.P.S. I have seen they are secured partially with a drop of wax, partially with paint. What is the material you would recommend for re - securing them?

9th Jul 2007, 10:00 pm	#7
Brian R Pateman Nonode Join Date: Jun 2005 Location: Western Lake District, Cumbria (CA20) - UK Posts: 2,136	Re: FM tuner and IF adjustment on '55 Minerva For the ultimate professional approach use "Loctite." From a practical point of view I use up my wife's old nail varnish - cheap and such pretty colours! Regards, __________________ Brian

26th Jul 2007, 1:22 am	#8
Richard_66 Retired Dormant Member Join Date: May 2007 Location: Vienna, Austria Posts: 9	Re: FM tuner and IF adjustment on '55 Minerva hi, first, thanks alot to Steve and Brian for their valuable hints! It really took me some time now (why can't women share our passion for old radios?). I borrowed a signal generator and a good oscilloscope. Of course, Steve had been right and I had inadverdently misaligned the IF both on FM and AM on one of the Minerva's. However, meanwhile I managed to restore the alignment. For alignment of the FM IF, I put all IF stages to the same resonance frequency (i.e. 10.7MHz). A slight difference in resonance frequency would make the frequency response look better (i.e. with a flat top), but the radio would not sound better and the magic eye would be misleading. The frequency response of the IF filters is shown in the first picture. The signal generator was sweeping from 10.3 to 11.1MHz. The oscilloscope shows an inverted and a bit funny 'envelope' curve, but I think one can conclude how the frequency response actually looks like. Then I tried the hints for widening and flattening the frequency response of the IF section, as proposed in the link that Steve posted above. With 27kOhms across the capacitors of both filter stages, the frequency response looked like in picture 2 (same frequency span of course, but higher gain). So the curve is much wider ( I think this is actually too much, I will use larger resistors eventually). However, I did not succeed so far in making the range of the ratio detector wider. The radio already sounds much cleaner, but is still difficult to tune and reacts unpleasantly to any thermal drift. The response of the ratio detector is shown in the third picture (same frequency span). Its's linear range is just around +/- 100kHz. Would you recommend to try to modify the ratio detector? I have posted a circuit diagram above, could you please give me a hint where to start? thanks in advance, and best regards, Richard Attached Thumbnails

26th Jul 2007, 7:26 pm	#9
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: FM tuner and IF adjustment on '55 Minerva I can't quite see what is what on your circuit diagram so I'm winging a bit here, but that's part of the fun. There's an Electrolytic, Looks like 32uF. Across this is a smaller cap, 4nF and a resistor 47K. Change the electrolytic and the others if need be. Then, set it up. You'll find the way to do this on this page: http://www.vintage-radio.com/repair-...alignment.html It's under IF Alignment. Cheers, Steve P __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

26th Jul 2007, 10:35 pm	#10
Richard_66 Retired Dormant Member Join Date: May 2007 Location: Vienna, Austria Posts: 9	Re: FM tuner and IF adjustment on '55 Minerva Thanks, Steve! The electrolytic (originally 3.2uF) is already a new one! The smaller cap is a ceramic one ( cannot test it, but it is unlikely to fail) and the resistor is ok. The ratio detector circuit is already centered correctly. I have the impression that the set is already working as Mother Nature intended it to do, but it cannot cope with the higher modulation depth of current radio stations. So I was looking for a way to change the ratio detector in order to get a wider linear range (e.g. +/- 150kHz instead of +/- 100kHz). best regards, Richard

29th Jul 2007, 3:34 am	#11
Richard_66 Retired Dormant Member Join Date: May 2007 Location: Vienna, Austria Posts: 9	Re: FM tuner and IF adjustment on '55 Minerva hi, I just had another 'session' on my victim. Success, what concerns the ratio detector: A quite small resistor (just 10kOhms this time) across the final IF transformer (which actually builds the ratio detector) did the trick. Not a very glorious finding, as the measure was in line with the instructions in http://www.vintage-radio.com/repair-...rf-stages.html). The attached pics show the demodulated signal without and then with dampening (in both cases sweeping from 10.3 to 11.1MHz, but different gain). In the latter picture, the slope of the ratio detector's output is reduced, and the linear range is extended, Seems the reception has become audibly clearer since then. What unfortunately remains: I also noticed that the preselection in the tuner section is quite narrow. However I am not very motivated to touch the tuner ... best regards, Richard Attached Thumbnails

29th Jul 2007, 9:24 am	#12
PWH Heptode Join Date: Mar 2003 Location: Waiheke Island, New Zealand Posts: 503	Re: FM tuner and IF adjustment on '55 Minerva If you have another ecc85 in a set which gives good reception swap it and see. ECC85's go low emission. I have had sets with no FM. Changing the ECC85 restored it perfectly

29th Jul 2007, 11:04 pm	#13
Richard_66 Retired Dormant Member Join Date: May 2007 Location: Vienna, Austria Posts: 9	Re: FM tuner and IF adjustment on '55 Minerva Thanks for the hint, PWH! I have swapped the ECC85 against a well-working, newer piece. However it would not get better. Seems that this particular tuner (of the Minerva Record) has its limits. Anyhow, the FM reception has much improved already. I have now also tried the same procedure - IF broadening and adjustment, together with shifting the FM oscillator and preselection up 4MHz, to get my favourite station - on the large set (Minerva Consul). This time I was rewarded with perfect sound (out of five loudspeakers, many new caps and a complete set of new valves). For the 'Record', there is obviously still some room for improvement - but probably I was just expecting too much ... best regards, Richard

29th Jul 2007, 11:17 pm	#14
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: FM tuner and IF adjustment on '55 Minerva This is probably the case. FM is more crowded now and a lot more processing is used. Some of the early FM units did have their limits, and the transmissions now can drift about more before something is done about them. In years gone by, the Readings and Measurements were taken at least once a day. Not now though. I'll stop there - as some on this forum know, the downhill slide of Transmission is a constant gripe of mine. Who shouted 'One of Many'... Cheers, Steve P __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?