UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Other Discussions > Homebrew Equipment

Notices

Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members.

Closed Thread
 
Thread Tools
Old 26th Jul 2011, 7:20 am   #1
odyseus
Diode
 
Join Date: Jan 2007
Location: Fareham
Posts: 4
Default 6S3T Spontaflex receiver.

Quote:
Originally Posted by jim_jobe View Post
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

Last edited by Darren-UK; 26th Jul 2011 at 11:19 am. Reason: Split from thread linked via quote.
odyseus is offline  
Old 26th Jul 2011, 11:58 am   #2
neon indicator
No Longer a Member
 
Join Date: Jun 2010
Location: Co. Limerick, Ireland.
Posts: 1,183
Default 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.
neon indicator is offline  
Old 26th Jul 2011, 7:43 pm   #3
jim_jobe
Heptode
 
Join Date: Nov 2004
Location: Ripon, N.Yorkshire, UK.
Posts: 782
Default Re: 6S3T Spontaflex receiver.

Mine works just fine with just an earth and no aerial,
Jim
jim_jobe is offline  
Old 27th Jul 2011, 10:22 am   #4
jim_jobe
Heptode
 
Join Date: Nov 2004
Location: Ripon, N.Yorkshire, UK.
Posts: 782
Default 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
jim_jobe is offline  
Old 27th Jul 2011, 11:57 am   #5
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 18,453
Default 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.
paulsherwin is offline  
Old 27th Jul 2011, 2:57 pm   #6
odyseus
Diode
 
Join Date: Jan 2007
Location: Fareham
Posts: 4
Default 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
odyseus is offline  
Old 28th Jul 2011, 10:11 am   #7
jim_jobe
Heptode
 
Join Date: Nov 2004
Location: Ripon, N.Yorkshire, UK.
Posts: 782
Default Re: 6S3T Spontaflex receiver.

This is my cheap and cheerful arrangement! Note 30V transformer used as choke.
Jim
Attached Thumbnails
Click image for larger version

Name:	SPONTAFLEX 005.jpg
Views:	304
Size:	98.5 KB
ID:	54427   Click image for larger version

Name:	SPONTAFLEX 006.jpg
Views:	230
Size:	103.4 KB
ID:	54428  
jim_jobe is offline  
Old 28th Jul 2011, 10:55 am   #8
AlanC
Pentode
 
AlanC's Avatar
 
Join Date: Jul 2006
Location: Sheffield, South Yorkshire, UK.
Posts: 241
Default 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...
AlanC is offline  
Old 29th Jul 2011, 10:22 am   #9
jim_jobe
Heptode
 
Join Date: Nov 2004
Location: Ripon, N.Yorkshire, UK.
Posts: 782
Default 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
jim_jobe is offline  
Old 29th Jul 2011, 10:59 am   #10
neon indicator
No Longer a Member
 
Join Date: Jun 2010
Location: Co. Limerick, Ireland.
Posts: 1,183
Default 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.
neon indicator is offline  
Old 29th Jul 2011, 11:44 am   #11
jim_jobe
Heptode
 
Join Date: Nov 2004
Location: Ripon, N.Yorkshire, UK.
Posts: 782
Default Re: 6S3T Spontaflex receiver.

Quote:
Originally Posted by neon indicator View Post
Probably end up more complex than a superhet.
That's the problem!
Jim
jim_jobe is offline  
Old 30th Jul 2011, 9:27 pm   #12
AlanC
Pentode
 
AlanC's Avatar
 
Join Date: Jul 2006
Location: Sheffield, South Yorkshire, UK.
Posts: 241
Default 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
Click image for larger version

Name:	IMG_5543.jpg
Views:	170
Size:	71.5 KB
ID:	54510  
__________________
Always expect the unexpected...
AlanC is offline  
Old 2nd Aug 2011, 6:55 pm   #13
jim_jobe
Heptode
 
Join Date: Nov 2004
Location: Ripon, N.Yorkshire, UK.
Posts: 782
Default 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
jim_jobe is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 5:14 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Copyright ©2002 - 2019, Paul Stenning.