Receiver Circuit wanted - Page 4 - UK Vintage Radio Repair and Restoration Discussion Forum

Herald1360 · 31st Dec 2013, 11:35 pm

Attached is snip of A358 oscillator circuit.

If you edit out the primary of the SW coil and close S9 and S13, you get a C-L-C pi arrangement. Effectively Fernseh's sketch has the tuning capacitor and anode coupling capacitor connections to the coil transposed.

Ahhh, a quick refresher courtesy of Dr Google tells me it's a Colpitts oscillator

Skywave · 1st Jan 2014, 12:59 pm

Thank you: that arrangement makes sense!

Al. / Jan. 1st., 2014 //

Mike Brett · 12th Jan 2014, 12:58 pm

At last as promised here is my version of the S.W.2 built for the M.W. broadcast band. Strangely enough it worked first time although the reception could be improved, it might need some extra screening around the valves. I wanted to build the chassis a bit different to my usual standard aluminium box approach and it worked out very well. Not an easy set to tune in it has to be said but interesting to play with.

Mike

G6Tanuki · 12th Jan 2014, 1:19 pm

Nice! I really like the use of school-geometry protractors as tuning dials. Construction-style is interesting too.

Aren't you worried though that putting the speaker so it points directly at the tuning-capacitors could be a cause of microphony?

Mike Brett · 12th Jan 2014, 3:58 pm

I must admit that I thought there might be a problem placing the speakers in such a position, but nothing ventured as they say, as it turns out it wasn't a problem.I normally build a radio then wonder where to put the speaker, there is normally no room left on the front panel, so this time I built the radio around the speaker. Done some tweaking on the coils and now reception is perfect. It now tunes 475 kHz to 1800 kHz. Glad you like the dials,came from kids geometry sets, 99 p from ALDI.
Mike

AC/HL · 12th Jan 2014, 5:10 pm

Looks like a candidate for a Bulletin article to me.

G6Tanuki · 12th Jan 2014, 7:32 pm

Quote:

Originally Posted by Mike Brett

Glad you like the dials,came from kids geometry sets, 99 p from ALDI

If it works, go for it! Definitely an intriguing bit of design-engineering.

How easy was it to drill/countersink the protractors without them cracking? From memory of the "Helix" brand ones we had at school in the 1970s they were rather brittle. Even the thick plastic of car number-plates is prone to cracking if your drill suddenly 'bites'.

[Reason I ask is that I have an idea to use a protractor as the capacitor indicator on an antenna-tuner I've built]

Mike Brett · 13th Jan 2014, 10:04 am

Drilling of the protractors was not a problem, perhaps these being a cheaper version than the Helix ones they where of a softer plastic, not sure. The only precaution I took was to drill a very small hole to start,1 mm then go up in 1/2 mm stages to 6.5mm for the spindle hole.
Mike

31st Dec 2013, 11:35 pm	#61
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Receiver Circuit wanted Attached is snip of A358 oscillator circuit. If you edit out the primary of the SW coil and close S9 and S13, you get a C-L-C pi arrangement. Effectively Fernseh's sketch has the tuning capacitor and anode coupling capacitor connections to the coil transposed. Ahhh, a quick refresher courtesy of Dr Google tells me it's a Colpitts oscillator Attached Thumbnails __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

1st Jan 2014, 12:59 pm	#62
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: Receiver Circuit wanted Thank you: that arrangement makes sense! Al. / Jan. 1st., 2014 //

12th Jan 2014, 12:58 pm	#63
Mike Brett Retired Dormant Member Join Date: Dec 2005 Location: Wisbech, Cambridgeshire, UK. Posts: 452	Re: Receiver Circuit wanted At last as promised here is my version of the S.W.2 built for the M.W. broadcast band. Strangely enough it worked first time although the reception could be improved, it might need some extra screening around the valves. I wanted to build the chassis a bit different to my usual standard aluminium box approach and it worked out very well. Not an easy set to tune in it has to be said but interesting to play with. Mike Attached Thumbnails

12th Jan 2014, 1:19 pm	#64
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: Receiver Circuit wanted Nice! I really like the use of school-geometry protractors as tuning dials. Construction-style is interesting too. Aren't you worried though that putting the speaker so it points directly at the tuning-capacitors could be a cause of microphony?

12th Jan 2014, 3:58 pm	#65
Mike Brett Retired Dormant Member Join Date: Dec 2005 Location: Wisbech, Cambridgeshire, UK. Posts: 452	Re: Receiver Circuit wanted I must admit that I thought there might be a problem placing the speakers in such a position, but nothing ventured as they say, as it turns out it wasn't a problem.I normally build a radio then wonder where to put the speaker, there is normally no room left on the front panel, so this time I built the radio around the speaker. Done some tweaking on the coils and now reception is perfect. It now tunes 475 kHz to 1800 kHz. Glad you like the dials,came from kids geometry sets, 99 p from ALDI. Mike

12th Jan 2014, 5:10 pm	#66
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Receiver Circuit wanted Looks like a candidate for a Bulletin article to me.

13th Jan 2014, 10:04 am	#68
Mike Brett Retired Dormant Member Join Date: Dec 2005 Location: Wisbech, Cambridgeshire, UK. Posts: 452	Re: Receiver Circuit wanted Drilling of the protractors was not a problem, perhaps these being a cheaper version than the Helix ones they where of a softer plastic, not sure. The only precaution I took was to drill a very small hole to start,1 mm then go up in 1/2 mm stages to 6.5mm for the spindle hole. Mike