Sonora SF5 - Low HT - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

richieyork · 17th Jun 2020, 4:03 pm

HT high voltage resolved. The previous repairer (who'd modified it to use an EL84) had connected the speaker energiser/choke coil the wrong way around!! Grr!!!

HT voltages now in the range of 245v. Happy! Thanks for all the suggestions

So, any suggestions on how to remove the speaker cone 'centering fixment (looks like a 45 rpm adaptor) from the paper cone with out damaging the cone? It's glued on. What would be good to dissolve the glue? The speaker voice coil is dragging slightly and i'm now feeling brave to have a go at fixing it...
Cheers
Rich

Herald1360 · 17th Jun 2020, 4:04 pm

Quote:

Originally Posted by richieyork

So, HT. Both my DMM and analogue meters are giving 345v DC on the cathode of the CV1708 f/w rectifier valve - this drops to around 294v on the anode of the output valve. The CV1708 replaced the original "80" valve - I was advised this was a suitable substitute (not on this website)...

Cheers
Rich

CV1708 spec cites type 80 as its prototype so should be just fine.

PJL · 17th Jun 2020, 4:05 pm

The external spider makes it easy. You need some very thin but stiff plastic sheet, I have some mylar film but you should be able to find something similar. You cut some 1cm wide strips tapering towards the end maybe 10 cm long. Unscrew the central screw and insert the strip between each of the spider legs to space the voice coil centrally then do the screw back up. It take a bit of patience and you sometimes need to work around the coil with some strip to remove dust/rust and very carefully use the vacuum on it whilst holding the cone in place. Just don't break the spider!

I assume it looks similar to this http://radiomuseum.co.uk/a92.html

I guess you mean the energiser coil was not wired in circuit?

richieyork · 17th Jun 2020, 8:39 pm

Quote:

Originally Posted by PJL

The external spider makes it easy. You need some very thin but stiff plastic sheet, I have some mylar film but you should be able to find something similar. You cut some 1cm wide strips tapering towards the end maybe 10 cm long. Unscrew the central screw and insert the strip between each of the spider legs to space the voice coil centrally then do the screw back up. It take a bit of patience and you sometimes need to work around the coil with some strip to remove dust/rust and very carefully use the vacuum on it whilst holding the cone in place. Just don't break the spider!

I assume it looks similar to this http://radiomuseum.co.uk/a92.html

I guess you mean the energiser coil was not wired in circuit?

Genius!!! I was expecting i'd have to do a lot more to get the speaker sorted! Thank you

Yes, it looked like the Murphy speaker.

Re the power supply, due to a wiring mishmash basically the full HT was going to the set and the energiser coil was in series to the anode of output valve via the output transformer. It was a bodge job, along with the 'adapted EL84. No wonder the set had died previously.

Thank you for your invaluable help.

richieyork · 20th Jun 2020, 4:00 pm

Hi all

Just to conclude the radio is now working pretty well and i've done all I can. The owner is delighted and a beautiful piece of vintage electronic history lives on to be enjoyed a little more.

A big thank you to all on here that helped/contributed in some way or another in helping me restore this wonderful old set.

Rich.
ps my next project is a Pye Achoic 1003 (?) record player...how i love these...not..expect to hear from me again in a new thread :<)

17th Jun 2020, 4:03 pm	#21
richieyork Pentode Join Date: Dec 2010 Location: York, North Yorkshire, UK. Posts: 212	Re: Sonora SF5 - Low HT HT high voltage resolved. The previous repairer (who'd modified it to use an EL84) had connected the speaker energiser/choke coil the wrong way around!! Grr!!! HT voltages now in the range of 245v. Happy! Thanks for all the suggestions So, any suggestions on how to remove the speaker cone 'centering fixment (looks like a 45 rpm adaptor) from the paper cone with out damaging the cone? It's glued on. What would be good to dissolve the glue? The speaker voice coil is dragging slightly and i'm now feeling brave to have a go at fixing it... Cheers Rich

17th Jun 2020, 4:05 pm	#23
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Sonora SF5 - Low HT The external spider makes it easy. You need some very thin but stiff plastic sheet, I have some mylar film but you should be able to find something similar. You cut some 1cm wide strips tapering towards the end maybe 10 cm long. Unscrew the central screw and insert the strip between each of the spider legs to space the voice coil centrally then do the screw back up. It take a bit of patience and you sometimes need to work around the coil with some strip to remove dust/rust and very carefully use the vacuum on it whilst holding the cone in place. Just don't break the spider! I assume it looks similar to this http://radiomuseum.co.uk/a92.html I guess you mean the energiser coil was not wired in circuit? Last edited by PJL; 17th Jun 2020 at 4:12 pm.

20th Jun 2020, 4:00 pm	#25
richieyork Pentode Join Date: Dec 2010 Location: York, North Yorkshire, UK. Posts: 212	Re: Sonora SF5 - Low HT Hi all Just to conclude the radio is now working pretty well and i've done all I can. The owner is delighted and a beautiful piece of vintage electronic history lives on to be enjoyed a little more. A big thank you to all on here that helped/contributed in some way or another in helping me restore this wonderful old set. Rich. ps my next project is a Pye Achoic 1003 (?) record player...how i love these...not..expect to hear from me again in a new thread :<)