Grundig Elite-Boy 500 maintenance manual in German - can anyone help?

[simpsons]

Hi again Mike.

You don't need to use a FM signal generator, a FM broadcast will be fine for AM rejection adjustment on the discriminator; using the DC motor or other man made interference to tweak it.

Make sure the signal is kept as low as possible, best a weak station so that tuning the radio to the loudest sound is easy, then turn the core for minimum noise and/or use the man made interference as mentioned by another member.

You should only need a small adjustment, either way watch out the core doesn't become damaged.

An FM signal generator will let you see how the response curve looks but, in my opinion, I would read up on how others have used such equipment before trying it out yourself. You only need to be a few kHz off 10.7 mHz and the whole alignment thing can go "die toilette runter." A Grundig technical term.

Chris

[tri-comp]

Hello,

Sorry, I didn't see this thread until today.
Attached is the alignment instructions in English for the Grundig Yacht Boy 208_209_210.
I believe you will find the instructions to fit very close with the Elite Boy 500 and to a lot of similar radios.

Rgds,

/Torben

[Boulevardier]

Thanks Torben. Had a quick look, and you're right - the Yacht Boy's ratio detector circuit is almost identical to the Elite 500 - with one puzzling difference - the YB circuit had a variable resistor in one diode "leg"where the EB has only a fixed (680 ohm) resistor. I know that it is normal to have such a variable resistor in this position, I just wonder why the Yacht Boy needs one but the Elite Boy doesn't?

Anyone have any ideas?

Mike

[tri-comp]

Variable compensation for a spread in production for fwd. voltage characteristics ?
I know Germanium diodes were supplied as a matched pair in the past.
Possibly to avoid the need for balancing circuitry like the potentiometer you refer to.

Rgds,

/Torben

[MotorBikeLes]

If you look back to my previous post, a variable resistor is often fitted to get the optimum AN interference free reception, with the little DC (commutator) motor running to simulate worst AM interference situation.
Les.

[Boulevardier]

Thanks Les, what was puzzling me is why the Elite-Boy 500 model was thought not to need that variable resistor, when most of its Grundig stable companions seem to have one. All of them would be subject to the same AM rejection problems.

Mike

[Argus25]

Fortunately the issue of requiring the alignment instructions for a specific FM or AM radio is solved by another method:

The "alignment instructions" of nearly every typical radio of that era, with the circuit configuration you have, is spelled out very very clearly (in English no less) by the manufacturers of the generators intended to do the alignment at the time.

They show how & where the generator and scope should be connected, what padding resistors are required etc.

For example, if you look in the service manual for the Philips PM5326 generator (A generator that I have often recommended) I'm pretty sure it clearly shows you how to do the FM alignment, including the ratio detector. (I will look at the manual tonight)

So if you got a copy of that manual (and preferably the generator too) you are already 98% there. It pays to read the manuals of good test instruments, many of the answers to your concerns will be found there.

The manual is on line, have a look at manual pages 20 to 30:

http://bee.mif.pg.gda.pl/ciasteczkow.../Pm5326%20.pdf

[Argus25]

Originally Posted by simpsons

You don't need to use a FM signal generator, a FM broadcast will be fine for AM rejection adjustment on the discriminator; using the DC motor or other man made interference to tweak it.

It would take a pretty brave person to suggest a company like Philips went to all the trouble and spent all the R&D money, hired many well educated & professional RF engineers to build an FM capable sweep generator with a very accurate high resolution digital frequency display (based on an Intersil IC and crystal timebase) and accurate markers, because it wasn't a requirement to properly align an FM radio with a discriminator or a ratio detector. And that it could have been done satisfactorily with a "listening test". Does that sound right ?

It is not just about AM rejection, it is about ensuring a symmetrical linear translation function of +/- frequency offset with the detector output over a range that corresponds to the max frequency deviation. So it requires the sweep, with markers, to be sure it is correct. Especially in the case, that the fundamental fault is that it appears that the output from the detector, in the OP's radio, is distorted in some way.

[simpsons]

Argus 25, I am that brave gentleman.

Why? Because first the member is new to fault finding and FM radio IF circuit design. Notwithstanding the alignment instruction being written in German or English, I believe it is necessary to understand a lttle of what you are doing when repairing a transistor radio especially if the fault is illusive.

Secondly, aligning IF circuits requires experience and I understand that Mike has not yet used of a scope and wobbulator to align IF and discriminator transformers. Crystal markers and response curves are very informative when you know what they mean but, I would be cautious to recommend such equipment to effect what could be adjustment of one core, without a helping hand.

Third, from Mikes description of his attempt to repair the radio, he has only adjusted the core of the ratio detector, a tweek often refered to in this forum without use of a wobbulator. I do agree for optimimum results it maybe necessary but were talking a mono transistor radio.

I did think that Mike's report of "a bit of distortion on the audio output" needed following up just in case he's barking up the wrong tree, so to speak.

I do of course fully agree that in a manufacturing environment, the use of a proper display and signal source is without question the proper way of aligning the IF strip but the user must know what is required.

In the case of Grundig their AM IF transformers, a symetrical bandswidth of 4.3kHz is often specified and the IF not just peaked for maximum output. For FM I'm unable to find the spec included in their service manual. No doubt because it is an industry standard, as you say detailed in the wobbulator user guide.

Chris

[simpsons]

Mike,

There is a useful article called "Realigning FM receivers" published by The Radio Museum which to my eyes will help someone new to the art understand why and how the IF and discriminator transformers should be adjusted and how the oscilliscope display will look or when using a high impedence volt meter, which then was called a VTVM - vacuum tube voltmeter. Not an old AVO meter which you cannot use.

Although it does referer to valve circuits for US readers readers, the steps shown equally apply to transistor radios. Note your radio uses a Ratio Detector.

You will find it on https://www.radiomuseum.org/forumdat...1952%20OCR.pdf

The deviation or sweep for the IF response required for mono is 150 kHz and for stereo 200kHz, although to accomodate the use of Optimod compression it may be necessary to now use 200 kHz for both. Perhaps other members may have a view on this. In addition, have a look at the posts on this site RE: "FM Deviation"

Chris

[Boulevardier]

Thanks Argus25, your pointer to the PM5326 manual is very useful and generalisable.

Argus25 and Simpsons - on alignment by ear versus alignment "by the book", you are, of course, both right - it's horses for courses. If aligning large numbers on an assembly line, then you need a quick, repeatable method that gives the same results each time and doesn't rely on individual operators' ears, foibles, etc. If (like me) you're just doing it for personal use and you aren't going to make a habit of judging sound quality with laboratory instruments, then simpler techniques (or even "by ear") is probably more than adequate.

Me? For this set I just want a radio that's neat, cheap to run (batteries last at least a week or two under constant use), and gives sound quality that doesn't grate in any way. So, sibilance and some distortion don't quite cut the mustard. Thus my efforts to sort them. Just how "technical" I need to get to sort that is something I'm working through now. Maybe I will have to do a full realignment (I really hope not, but I've just got hold of an FM generator in case), but maybe simpler solutions (just focusing on the ratio detector, de-emphasis components, etc) will do the trick. Most of the electronics "stuff" I've been doing since I was a teenager has focused on LF/audio equipment, so RF, particularly VHF FM, is a new departure for me - thus the impression of floundering around a bit.

I'm really grateful for all the thoughts on here; I'm finding them all very instructive and useful, and I'm enjoying expanding my knowledge. I am currently trying to fit in the time to follow them up with time-sensitive commitments to other work (nothing to do with electronics).

Thanks again to all!

Mike