Confusing Sobell 519P.

[Riccampbell]

I am utterly confused regarding a Sobell 519P radio. I have a circuit diagram from the site archives but it seems to bear no resemblance to my set. The diagram is for a 519, not a 519P I don't know whether or not this is the problem. An example is the 519 has a 5Z4G rectifier whereas my set has a U50, different altogether. There are capacitors and resistors in the set which do not correspond with the diagram, which is very basic anyway. The set does work, but not very well hence the sort out.


I have looked everywhere for any reference to a 519P but have drawn a complete blank. I did come across a vague reference to a McMichael set, is it that the two firms are one? or did one take over the other? like Philips and Cossor, I don't know. Any clues very welcome, Ric.

[jonnybear]

It is possible someone has popped in a U50 instead of a 5Z4, I think the easiest way to find out what you have is with a couple of pictures of the set and chassis.You could probably sort most of the problems, by replacing the wax capacitors. Yes McMichael, Sobell, Masteradio, were all part of GEC.
John

[Andrewausfa]

Hi Ric,

I think the 'P' stands for Plastic so just the cabinet style and possibly not any circuit changes.
I assume yours has Bakelite cabinet?

Andrew

[Riccampbell]

There is a picture of the set already on the site, posted on the 5th March, 2012 by MICKJJO.

https://www.vintage-radio.net/forum/...ad.php?t=80827

(I found it on Google under "Sobell caravan shaped radio" " it took me to the site and was the first in the list. This followed a thread concerning a "Caravan shaped radio "on the site; there is a thumbnail there my set is the second one, at the top.


As for the rectifier, I see what you mean, the 5Z4 is indirectly heated but the pin outs are the same, so you could swap them. There is still something odd about the wiring diagram though.


I have replaced all the wax capacitors and also found a resistor that was reading very high, I am waiting for some parts so I can fire it up, I will see how it goes and post the results. Cheers, Ric.

[Riccampbell]

The plot thickens, having just spent the last hour or so setting the alignment as per the instructions on the service sheet (It was a mile out, especially the IF) and after fitting the new capacitors that have arrived I confidently turned the set on.

It works, but still with problems. SW is very good, all sorts of stations. MW is OK but with quite a bit of background crackling (I have tried servicol on the wave change switch and the volume pot, which I may change) LW, no background noise but no reception, that is at places on the scale where stations should be I get a humming sound but that's all.

What am I doing wrong? Cheers, Ric.

[Riccampbell]

I do try to sort out problems using my limited knowledge, but in most cases I end up baffled. In this case, my Sobell, there seems to be something wrong with the alignment I can't get to grips with.

I have a service sheet from the site and my first attempt I got reasonable results, however on still having the problems listed in my last post I decided to check my work to see if I had done something wrong. The I.F was OK, but when I got to LW I found I could set C19 and C3 but not L12/13 and L6/7. No matter where the cores were made no difference at all to the set. I have replaced C12 & C11 (both 100 pf) I will attempt to post a circuit diagram on the site. Any ideas gratefully received. Ric.

[AC/HL]

One post removed (Rule B12)

[jonnybear]

First of all you say when you realigned the radio it was miles out, normally this is not normally the case unless it had been twiddled, are you sure your signal generator is set up and working correctly, other than that check all switch contact continuity cold with meter set at low ohms.
John

[Stylo N M]

Hi,

Have you checked to see if any of the cores are open circuit?

paul.

[boxdoctor]

Just a thought - check the long wave aerial coil for continuity. I do not know this set, but Johnnybear's suggestion regarding the checking of the signal generator is a very good point. Un-twiddled sets are rarely very far out of alignment. If they are, its usually faulty trimmers/mica capacitors. Tony

[Riccampbell]

Many thanks for advice, I will set too and do the checks. Regarding the alignment, the set had been "got at". I know this because it was me, as a spotty young lad, who did the fiddling. The set has been in the family since the early 50's and I would dearly like to make amends. Also I know someone local with a frequency counter so I can check my gen. Cheers, Ric.

[Riccampbell]

Further to my last posting I had a visit from a nearby site member, very informative. After a short while a fundamental error was spotted. The drive cord had been arranged the wrong way round, so that with the cursor at the top of the scale the tuning cap was fully open. I had noticed this, but assumed the service sheet had a mistake printed. Bad mistake on my part.

I rectified the problem, what a fiddle these drive cords can be, plug in the generator and follow the instructions. Incidentally my visitor bought a frequency counter with him and checked my generator which turned out to be surprisingly accurate. No success at all, MW works in a fashion but no SW or LW. With the gen connected and set as per the sheet most of the coils and trimming caps seem to do nothing. I have spent many fruitless hours experimenting and trying various combinations but all to no avail.

All suggestions gratefully received! I can only assume I have made a fundamental error somewhere along the line, but can't see where. Is it possible that something has gone wrong regarding the RF coils? I can't really see how they are fitted, there is a kind of cap nut above the chassis with a brass screw sticking out. Also can the trimmer caps give problems and if so how do these come apart, it looks to me like some serious de-soldering is required. Cheers, Ric.

[Herald1360]

Have close look at the other end of the brass screws- is there a greyish cylindrical lump? If so, it'll be a magnetic core which varies the inductance as it is screwed in or out from the centre of the coil.

Sets with these adjustable cores will require both trimmers and cores to be adjusted in line with service data to set up the tuning. Usually the cores will be set somewhere close to the LF end of each band and the trimmers near the HF end in an iterative process to get best results.

Unless the set has been twiddled with before, these settings don't usually drift off by themselves unless there are other faults. Total lack of signals is more likely to be bad switch contacts or perhaps a tired local oscillator.

[Andrewausfa]

Hi Ric,

Good to read you got the dial re-done. Are you hearing the tone of your signal generator, set to an appropriate frequency, anywhere on LW?

I still can't get over the size of your Nombrex signal generator!

Andrew

[Riccampbell]

I was hoping to have something positive to write, but alas no. I have had a good go at the set, including removing the capacitors from the coils to check cores and so on but there seems to be nothing amiss. Switch contacts, coil continuity and so on all seem OK.

I will give an example of how the tuning is; "set the generator to600kc/s tune the receiver to 500m Adjust L10/11, L5 & L3/4 for maximum output" So say the instructions. Firstly I get nothing at all unless I tune to around 350m and whatever I do there is no way of getting it right, and I have been at it for hours on end. At present I have SW a few stations on MW and no LW. To be honest it worked better with the IF a mile out and the tuning cap going the wrong way, but how on earth can this be?

The trouble now is all the adjustments are all over the place, is there a suitable formula for setting the alignment from scratch? The final problem I have is the circuit diagram I have bears little resemblance to reality, it makes very little sense all round.

Any ideas very welcome, Ric.

[wireful3]

Hi Ric, I don't know this set so the adjustments you made to set up don't mean much to me. I have had similar symptoms myself when the local oscillator was the wrong side of the signal frequency.

With the IF correctly aligned as you have done, SW performance can seem quite good but LW and MW odd. Have you tried the tuning the set to 600kHz and then varying the signal generator with a very strong signal to see if you get any response anywhere. If so the frequency received might give a clue. I have had some success injecting the signal directly to the frequency changer grid. This makes the RF section of the ganged tuning less effective and so not interacting with setting the local oscillator.

[Riccampbell]

I was hoping to have some good news about the old girl, but no. I cannot for the life of me get the alignment right, I have been through the set with a fine tooth comb and indeed fount some components with very odd values which I replaced with new parts of values stated in the service sheet. One of the large cans was also suspect so I have obtained new electrolytics and mounted them on a tag strip under the chassis so the cans can remain in place. All of my efforts made no difference; the set works well on SW, no reception on LW and only on MW by laboriously adjusting trimmers and coils until I could mange "Five live" and "Smooth radio", but nothing at all else.

If I try to align LW and MW I can get nowhere near; Tuning in the LW trimmer at 900m is not possible, but I do get the signal at about 1500m. The same on MW, nowhere at all. I get the same result with both my sig. gens (An Advance E1 and a Nombrex 27, for which I need a magnifying glass to set!) I have just disconnected the LW and MW trimmers and get very high values, instead of the 80pf as stated I get several hundred, this seems to me to be the fault, but has anyone else come across this one?

It would be difficult to fit other trimmers as the existing ones are fixed to the ends of the RF coils by metal clips, does this positioning matter? or can I mount them somewhere more convenient? All ideas very welcome, I would love to get to the bottom of this, Ric.

[julie_m]

If it works on SW, then it must all be OK downstream of the first IFT. (Try injecting modulated IF just to make sure, though.)

If you can get hold of an oscilloscope with a 10:1 probe, you should be able to get a look at what the local oscillator is doing. You've already eliminated virtually everything else .....

[Riccampbell]

I am still plugging away with the old Sobell, but to no avail. However, I have been trying to educate myself from books I have obtained, and one, Radio and audio servicing handbook by Gordon King, tells me the tuning gang should be fully out of mesh with the tuning cursor at low wavelengths, but my service sheet tells me the exact opposite, who is right? (Incidentally the set was strung like this initially by I re-jigged the drive to do the opposite, as per the service sheet, and nothing has worked right since)

Another thing is that Mr King, and W.T.Cocking, Wireless Servicing Manual, both recommend disabling the local oscillator and shorting out the AGC line whilst aligning the set, but there is no mention of this in the service sheet. It has to be said the service sheet in question does not comply with reality as far as the wiring goes, and is very basic in content. Probably alright for professionals but not the likes of me.

Any thoughts on this very welcome, Ric.

[Nuvistor]

Tuning gang full meshed is for low Frequency/longer wavelengths.

Tuning gang full Unmesheshed is for High frequency/shorter wavelengths.

With the gang fully meshed it will have more capacitance.

Frank