6S3T Spontaflex receiver. - UK Vintage Radio Repair and Restoration Discussion Forum

odyseus · 26th Jul 2011, 7:20 am

Quote:

Originally Posted by jim_jobe

All of Sir Douglas Hall's circuits are also available at www.radioconstructors.info/sdh/sdh.html
Jim

Hi,
Any of you guys ever built the 6S3T Spontaflex receiver?
I've built the Dec 1978 (Radio & Electronics Constructor) version and appears to work, but doesn't receive much ( I think I found one transmission last night across the whole tuning range) - So either it doesn't have much sensitivity or the short wave bands are extremely quiet these days (I haven't listened for over 10 years or more).
Maybe I really do need an earth as the article 'suggests' ??
All the best
John

neon indicator · 26th Jul 2011, 11:58 am

SW isn't great. It's also very dependent on your aerial and earth and which part of SW.

You might get away with "mains" earth. But my own "dedicated" Earth rods (4' galvanised "earthing" rods hammered) are less noisy with mains borne interference.

jim_jobe · 26th Jul 2011, 7:43 pm

Mine works just fine with just an earth and no aerial,
Jim

jim_jobe · 27th Jul 2011, 10:22 am

With the Germanium version, and presumably also the Silicon, it is very difficult to get smooth reaction with a 9V supply. Try reducing this for best results. Mine works best with 4.5V,
Jim

paulsherwin · 27th Jul 2011, 11:57 am

SW can indeed be very quiet at times. There's usually quite a few strong signals in the 49 and 41 meter bands in the late evening, so trying around 5-8MHz at that time is probably your best bet.

odyseus · 27th Jul 2011, 2:57 pm

I think I've sorted it now??
I had L3 (LT44) connected the wrong way round? It's now on the primary winding (2 wires) as I had originally connected it to the secondary (3 wires). An earth does make a difference on the higher bands.

I have taken a couple of photo's - I need to label the front and make a wooden box to surround it - Anyone have any good tips of making wooden boxes??

All the best

John

https://picasaweb.google.com/lh/phot...eat=directlink

https://picasaweb.google.com/lh/phot...eat=directlink

jim_jobe · 28th Jul 2011, 10:11 am

This is my cheap and cheerful arrangement! Note 30V transformer used as choke.
Jim

AlanC · 28th Jul 2011, 10:55 am

Jim, how well does it work? I built a Spontaflex (not this particular one) some years back and found it was okay... performed about the same as any other regenerative TRF would. I suspect the secret of success with Sir Douglas Halls' designs was to build them exactly as he did with the identical comonents. But there is no doubting they are a clever arrangement.

Re wooden box, I've used thin (~3mm) ply from B&Q, mark out all the pieces and cut it straight with a sharp narrow toothed saw so as not to split the wood. Then glue the edges with PVA and clamp it all together till it's dry. Then optionally sand, stain (if you wish) and coat with clear polyurethane varnish. If you flat it off with fine wet and dry and then re-coat, and repeat ad-nauseum, you'll eventually end up with a finish like a mirror.
HTH
Alan

jim_jobe · 29th Jul 2011, 10:22 am

It works pretty well. I have it alongside my Eddystone and can hear just about everything it picks up on the same frequencies although not so loudly of course. The main problem is in adjusting the reaction to just the right amount. I'm building the Silicon version at the moment (but taking my time over it!) and will fit a pot to vary the supply voltage into it plus any other mods I can think of (including an RF input attenuator so I can use a longer aerial). When it's finally finished I'll post it either here or in RB. I'll bear your box design in mind as well; sounds good,
Jim

neon indicator · 29th Jul 2011, 10:59 am

That's the major problem, the reaction/regenerative control. I've wondered as to the possibility of a 2nd feedback loop detecting RF and setting feedback at the critical level automatically. Probably end up more complex than a superhet.

jim_jobe · 29th Jul 2011, 11:44 am

Quote:

Originally Posted by neon indicator

Probably end up more complex than a superhet.

That's the problem!
Jim

AlanC · 30th Jul 2011, 9:27 pm

Well you've hit the nail on the head with that...

The pic below is the chassis and case I built for my short wave Spontaflex- and guess what, it IS now a superhet!!!

I've thought too in the past about using a feedback loop to detect the onset of oscillation and back off the gain of the detector, like some kind of AGC-
I wonder if its worth pursuing?

The picture also shows the cabinet construction I was on about in my earlier post.

jim_jobe · 2nd Aug 2011, 6:55 pm

Sounds like it's worth experimenting with.
I like your case. I'm building the silicon version into a metal case to try to stop hand capacitance effects which are a nuisance with the Ge version. I'm also going to make it cover several wavebands using plug in coils based on Din plugs and sockets.
Jim

26th Jul 2011, 11:58 am	#2
neon indicator Retired Dormant Member Join Date: Jun 2010 Location: Co. Limerick, Ireland. Posts: 1,183	Re: 6S3T Spontaflex receiver. SW isn't great. It's also very dependent on your aerial and earth and which part of SW. You might get away with "mains" earth. But my own "dedicated" Earth rods (4' galvanised "earthing" rods hammered) are less noisy with mains borne interference.

26th Jul 2011, 7:43 pm	#3
jim_jobe Heptode Join Date: Nov 2004 Location: Ripon, N.Yorkshire, UK. Posts: 782	Re: 6S3T Spontaflex receiver. Mine works just fine with just an earth and no aerial, Jim

27th Jul 2011, 10:22 am	#4
jim_jobe Heptode Join Date: Nov 2004 Location: Ripon, N.Yorkshire, UK. Posts: 782	Re: 6S3T Spontaflex receiver. With the Germanium version, and presumably also the Silicon, it is very difficult to get smooth reaction with a 9V supply. Try reducing this for best results. Mine works best with 4.5V, Jim

27th Jul 2011, 11:57 am	#5
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,947	Re: 6S3T Spontaflex receiver. SW can indeed be very quiet at times. There's usually quite a few strong signals in the 49 and 41 meter bands in the late evening, so trying around 5-8MHz at that time is probably your best bet.

27th Jul 2011, 2:57 pm	#6
odyseus Retired Dormant Member Join Date: Jan 2007 Location: Fareham Posts: 4	Re: 6S3T Spontaflex receiver. I think I've sorted it now?? I had L3 (LT44) connected the wrong way round? It's now on the primary winding (2 wires) as I had originally connected it to the secondary (3 wires). An earth does make a difference on the higher bands. I have taken a couple of photo's - I need to label the front and make a wooden box to surround it - Anyone have any good tips of making wooden boxes?? All the best John https://picasaweb.google.com/lh/phot...eat=directlink https://picasaweb.google.com/lh/phot...eat=directlink

28th Jul 2011, 10:11 am	#7
jim_jobe Heptode Join Date: Nov 2004 Location: Ripon, N.Yorkshire, UK. Posts: 782	Re: 6S3T Spontaflex receiver. This is my cheap and cheerful arrangement! Note 30V transformer used as choke. Jim Attached Thumbnails

28th Jul 2011, 10:55 am	#8
AlanC Hexode Join Date: Jul 2006 Location: Sheffield, South Yorkshire, UK. Posts: 312	Re: 6S3T Spontaflex receiver. Jim, how well does it work? I built a Spontaflex (not this particular one) some years back and found it was okay... performed about the same as any other regenerative TRF would. I suspect the secret of success with Sir Douglas Halls' designs was to build them exactly as he did with the identical comonents. But there is no doubting they are a clever arrangement. Re wooden box, I've used thin (~3mm) ply from B&Q, mark out all the pieces and cut it straight with a sharp narrow toothed saw so as not to split the wood. Then glue the edges with PVA and clamp it all together till it's dry. Then optionally sand, stain (if you wish) and coat with clear polyurethane varnish. If you flat it off with fine wet and dry and then re-coat, and repeat ad-nauseum, you'll eventually end up with a finish like a mirror. HTH Alan __________________ Always expect the unexpected...

29th Jul 2011, 10:22 am	#9
jim_jobe Heptode Join Date: Nov 2004 Location: Ripon, N.Yorkshire, UK. Posts: 782	Re: 6S3T Spontaflex receiver. It works pretty well. I have it alongside my Eddystone and can hear just about everything it picks up on the same frequencies although not so loudly of course. The main problem is in adjusting the reaction to just the right amount. I'm building the Silicon version at the moment (but taking my time over it!) and will fit a pot to vary the supply voltage into it plus any other mods I can think of (including an RF input attenuator so I can use a longer aerial). When it's finally finished I'll post it either here or in RB. I'll bear your box design in mind as well; sounds good, Jim

29th Jul 2011, 10:59 am	#10
neon indicator Retired Dormant Member Join Date: Jun 2010 Location: Co. Limerick, Ireland. Posts: 1,183	Re: 6S3T Spontaflex receiver. That's the major problem, the reaction/regenerative control. I've wondered as to the possibility of a 2nd feedback loop detecting RF and setting feedback at the critical level automatically. Probably end up more complex than a superhet.

30th Jul 2011, 9:27 pm	#12
AlanC Hexode Join Date: Jul 2006 Location: Sheffield, South Yorkshire, UK. Posts: 312	Re: 6S3T Spontaflex receiver. Well you've hit the nail on the head with that... The pic below is the chassis and case I built for my short wave Spontaflex- and guess what, it IS now a superhet!!! I've thought too in the past about using a feedback loop to detect the onset of oscillation and back off the gain of the detector, like some kind of AGC- I wonder if its worth pursuing? The picture also shows the cabinet construction I was on about in my earlier post. Attached Thumbnails __________________ Always expect the unexpected...

2nd Aug 2011, 6:55 pm	#13
jim_jobe Heptode Join Date: Nov 2004 Location: Ripon, N.Yorkshire, UK. Posts: 782	Re: 6S3T Spontaflex receiver. Sounds like it's worth experimenting with. I like your case. I'm building the silicon version into a metal case to try to stop hand capacitance effects which are a nuisance with the Ge version. I'm also going to make it cover several wavebands using plug in coils based on Din plugs and sockets. Jim