Sobell 516 radio help needed - UK Vintage Radio Repair and Restoration Discussion Forum

jelida · 9th Jun 2009, 11:16 pm

Hi Group,

I have recently been given a lovely Sobell 516 radio from 1947/8. I have checked the valves, and changed the capacitors. It works well on SW, nice and crisp. However on MW and LW, even with a long wire aerial station reception is very poor and hums loudly as you tune in. I presume this is due to poor alignment, and I have downloaded the servicing sheet from elsewhere on this site. However there is no chassis plan, and I am not presently experienced enough to tell which inductor and variable capacitor is which, to follow the instructions. I have signal generator, meters etc. I need help interpreting the chassis - Does anybody have a plan?

regards, Jerry

Steve_P · 9th Jun 2009, 11:39 pm

Sets of this age do tend to need an aerial it must be said. But a check on alignment and the also the antenna circuits won't go amiss.

Check the shielded cable and any caps you may have missed. It's all to easy to do. If it's not got a cap across the mains, fit an X2 type, 0.01uF or there abouts and see if that improves it.

Cheers,

Steve P.

yestertech · 10th Jun 2009, 8:48 am

Hi Jerry, I have listed manufacturers data for this set. Not sure if this is what you already have ? I will need to dig it out and see if it has a chassis layout

Andy

Station X · 10th Jun 2009, 9:11 am

The IF trimmer capacitors are simple enough to locate (they'll be inside or adjacent to the IF transformers) and it won't matter much what order they're adjusted in.

The group of three trimmers at top left of your under chassis picture are the local oscilator trimmers C17, C18 and C19. You can check which is which by tracing the wiring from the wavechange switch. This will enable the asociated coils to be identified too.

The group of four trimmers at bottom left are the aerial trimmers. Trace the wiring from the wavechange switch to identify these and their associated coils.

AlanBeckett · 10th Jun 2009, 10:27 am

Graham,
It has a 3-gang TC, but I can't see an rf amplifier. Is the aerial circuit double tuned like some Murphys?
Alan

Station X · 10th Jun 2009, 11:16 am

As you say there is no RF amplifier. I haven't fully studied the coil switching arrangements, but I assume double tuning is used.

PJL · 10th Jun 2009, 2:21 pm

If SW is working OK then the IF can't be too bad. You have thoroughly cleaned the waveband switch?

jelida · 10th Jun 2009, 6:54 pm

Thanks, all for your replies, a great help.and any more appreciated. The info that I have is the Radio Engineers Servicing Manual sheet downloaded elsewhere from this site. A chassis plan would still be useful.Now I have something to go on; but as regards the trimmers, from above chassis protrudes the slotted spindle that can be adjusted with an appropriate tool; below, a nut on the spindle can be adjusted. Do these achieve different things?
I will go over the contacts and check them
regards,
Jerry

yestertech · 11th Jun 2009, 3:58 pm

HI Jerry, hopefully the attached will assist in getting this set 'finished'

Andy

jelida · 11th Jun 2009, 10:47 pm

Thanks Andy, thats exactly what I need, hopefully I can sort it now.
regards,
Jerry

See_Mos · 19th Jun 2009, 8:42 pm

I don't have the circuit handy but if I remember correctly this set uses bandpass tuning on medium wave, hence the three gang tuning.

I would suggest checking the resistor values around the 6K8, the screen grid one tends to go high value.

It might be worth trying another 6K8 but usually the problem here is that the set stops working when tuning shorter wavelengths

Both of the big electrolytic capacitors should be disconnected and new capacitors fitted. It looks as if just one has been bypassed.

I currently have three of these sets. One has a bakelite case and is rusting away in the garage. One was used regularly until quite recently. The other has the half circle dial and was found in an old radio shop still in the box. The box was well rotten but the radio is OK.

Top Cap · 19th Jun 2009, 9:15 pm

Take care doing I.F. alignment on any radio like this one that uses trimmers instead of ferrite cores. The reason is that the trimmer screw has a good chance of being at HT potential and they are best adjusted with an insulated adjuster. Even the modern trimming tools can show too much metal on the edges at the tip end, I usually place a small heat shrink sleeve over this. This helps to ensure that there is no danger of accidentally shorting the trimmer to the I.F. can as you adjust.

9th Jun 2009, 11:16 pm	#1
jelida Pentode Join Date: Mar 2006 Location: Pontypool, South Wales, UK. Posts: 140	Sobell 516 radio help needed Hi Group, I have recently been given a lovely Sobell 516 radio from 1947/8. I have checked the valves, and changed the capacitors. It works well on SW, nice and crisp. However on MW and LW, even with a long wire aerial station reception is very poor and hums loudly as you tune in. I presume this is due to poor alignment, and I have downloaded the servicing sheet from elsewhere on this site. However there is no chassis plan, and I am not presently experienced enough to tell which inductor and variable capacitor is which, to follow the instructions. I have signal generator, meters etc. I need help interpreting the chassis - Does anybody have a plan? regards, Jerry Attached Thumbnails

9th Jun 2009, 11:39 pm	#2
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Sobell 516 radio help needed Sets of this age do tend to need an aerial it must be said. But a check on alignment and the also the antenna circuits won't go amiss. Check the shielded cable and any caps you may have missed. It's all to easy to do. If it's not got a cap across the mains, fit an X2 type, 0.01uF or there abouts and see if that improves it. 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...?

10th Jun 2009, 8:48 am	#3
yestertech Nonode Join Date: Dec 2002 Location: Coulsdon, Surrey, UK. Posts: 2,132	Re: Sobell 516 radio help needed Hi Jerry, I have listed manufacturers data for this set. Not sure if this is what you already have ? I will need to dig it out and see if it has a chassis layout Andy

10th Jun 2009, 9:11 am	#4
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Sobell 516 radio help needed The IF trimmer capacitors are simple enough to locate (they'll be inside or adjacent to the IF transformers) and it won't matter much what order they're adjusted in. The group of three trimmers at top left of your under chassis picture are the local oscilator trimmers C17, C18 and C19. You can check which is which by tracing the wiring from the wavechange switch. This will enable the asociated coils to be identified too. The group of four trimmers at bottom left are the aerial trimmers. Trace the wiring from the wavechange switch to identify these and their associated coils. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

10th Jun 2009, 10:27 am	#5
AlanBeckett Rest in Peace Join Date: Dec 2008 Location: Burton upon Trent, East Staffordshire, UK. Posts: 1,686	Re: Sobell 516 radio help needed Graham, It has a 3-gang TC, but I can't see an rf amplifier. Is the aerial circuit double tuned like some Murphys? Alan

10th Jun 2009, 11:16 am	#6
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Sobell 516 radio help needed As you say there is no RF amplifier. I haven't fully studied the coil switching arrangements, but I assume double tuning is used. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

10th Jun 2009, 2:21 pm	#7
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Sobell 516 radio help needed If SW is working OK then the IF can't be too bad. You have thoroughly cleaned the waveband switch?

10th Jun 2009, 6:54 pm	#8
jelida Pentode Join Date: Mar 2006 Location: Pontypool, South Wales, UK. Posts: 140	Re: Sobell 516 radio help needed Thanks, all for your replies, a great help.and any more appreciated. The info that I have is the Radio Engineers Servicing Manual sheet downloaded elsewhere from this site. A chassis plan would still be useful.Now I have something to go on; but as regards the trimmers, from above chassis protrudes the slotted spindle that can be adjusted with an appropriate tool; below, a nut on the spindle can be adjusted. Do these achieve different things? I will go over the contacts and check them regards, Jerry

11th Jun 2009, 3:58 pm	#9
yestertech Nonode Join Date: Dec 2002 Location: Coulsdon, Surrey, UK. Posts: 2,132	Re: Sobell 516 radio help needed HI Jerry, hopefully the attached will assist in getting this set 'finished' Andy Attached Thumbnails Last edited by Darren-UK; 11th Jun 2009 at 7:35 pm. Reason: To comply with forum rules.

11th Jun 2009, 10:47 pm	#10
jelida Pentode Join Date: Mar 2006 Location: Pontypool, South Wales, UK. Posts: 140	Re: Sobell 516 radio help needed Thanks Andy, thats exactly what I need, hopefully I can sort it now. regards, Jerry

19th Jun 2009, 8:42 pm	#11
See_Mos Hexode Join Date: Nov 2003 Location: Ossett, West Yorkshire, UK. Posts: 482	Re: Sobell 516 radio help needed I don't have the circuit handy but if I remember correctly this set uses bandpass tuning on medium wave, hence the three gang tuning. I would suggest checking the resistor values around the 6K8, the screen grid one tends to go high value. It might be worth trying another 6K8 but usually the problem here is that the set stops working when tuning shorter wavelengths Both of the big electrolytic capacitors should be disconnected and new capacitors fitted. It looks as if just one has been bypassed. I currently have three of these sets. One has a bakelite case and is rusting away in the garage. One was used regularly until quite recently. The other has the half circle dial and was found in an old radio shop still in the box. The box was well rotten but the radio is OK. Last edited by See_Mos; 19th Jun 2009 at 8:48 pm.

19th Jun 2009, 9:15 pm	#12
Top Cap Octode Join Date: Mar 2006 Location: Watford, Hertfordshire, UK. Posts: 1,270	Re: Sobell 516 radio help needed Take care doing I.F. alignment on any radio like this one that uses trimmers instead of ferrite cores. The reason is that the trimmer screw has a good chance of being at HT potential and they are best adjusted with an insulated adjuster. Even the modern trimming tools can show too much metal on the edges at the tip end, I usually place a small heat shrink sleeve over this. This helps to ensure that there is no danger of accidentally shorting the trimmer to the I.F. can as you adjust. __________________ Whether the Top Cap is Grid or Anode - touching it will give you a buzz either way!