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 22nd Jan 2018, 1:36 am   #1
MrBungle
Nonode
 
MrBungle's Avatar
 
Join Date: Jun 2016
Location: London, UK.
Posts: 2,553
Default Rewinding slug tuned IFTs

I am in the process of designing something and I've come across the requirement for a certain slug tuned inductor which appears to be unobtainable. Need 3.5uH. Doesn't seem to exist. Spectrum sell 5.3uH and 2.6uH cans so I've decided to try and rewind one with only one winding. I've got one 2u6L left to experiment with.

Some questions:

1. Is this a terrible idea?
2. How best to go about this? Do I start low and measure it with no core or do I stick the core in it and measure it?
3. Can I reuse the wire that is in them or should I buy some and just empty it and start again.
4. How can I crack one open without destroying it?

Alternatively does anyone know if I can tune the 5.3 or 2.6 coils into that range?
MrBungle is offline  
Old 22nd Jan 2018, 9:19 am   #2
merlinmaxwell
Dekatron
 
merlinmaxwell's Avatar
 
Join Date: Jul 2008
Location: Maidenhead, Berkshire, UK.
Posts: 7,725
Default Re: Rewinding slug tuned IFTs

Unwind a few turns from the 5u3?
MM
__________________
Cats have staff, it's dogs that have owners.
merlinmaxwell is offline  
Old 22nd Jan 2018, 9:48 am   #3
MrBungle
Nonode
 
MrBungle's Avatar
 
Join Date: Jun 2016
Location: London, UK.
Posts: 2,553
Default Re: Rewinding slug tuned IFTs

Will try that thanks. I’ve got to get hold of a 5u3L first hence checking viability. Haven’t rewound or dismantled any new ones before, only the big ones you used to get on very old transistor radio chassis’.
MrBungle is offline  
Old 22nd Jan 2018, 10:08 am   #4
Terry_VK5TM
Heptode
 
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 561
Default Re: Rewinding slug tuned IFTs

I can't remember if they have a couple of small crimps on the bottom that need to be straightened first, but basically you very carefully push them out of the can from the top (ie push down from the top so they slide out the bottom).
__________________
Terry VK5TM
http://www.vk5tm.com/
Terry_VK5TM is online now  
Old 22nd Jan 2018, 10:33 am   #5
MrBungle
Nonode
 
MrBungle's Avatar
 
Join Date: Jun 2016
Location: London, UK.
Posts: 2,553
Default Re: Rewinding slug tuned IFTs

Thanks - I just tried that and cut my finger open (doh!) so doing a more scientific method first.

I stuffed the 2u6L I have across a 100pF mica 1% capacitor and put a 47k resistor in series with the tuned circuit and stuffed it on my scope and signal generator. Solved resonant circuit equation for the two limits of the coil and it gives:

2u6L tuning range of 1.72uH to 4.17uH.

That's well within the tuning range of what I need so I'll probably grab some 2u6L's and just tune them appropriately.

I was half asleep last night at half past midnight when I was thinking this through. This morning I woke up with a "there must be an easier way here".

I'll grab some 5u3L's as well just in case they don't all tune into that range and I need some headroom.
MrBungle is offline  
Old 22nd Jan 2018, 10:50 am   #6
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 6,397
Default Re: Rewinding slug tuned IFTs

One other thing to consider - which I've done in the past - is wiring an additional coil in series [externally] to your variable one.

OK the tuning-range will be restricted so your choice of the additional coil's value needs to be made with intelligence - and it'll be unscreened - but the little axial-leaded coils that look like resistors are ideal for this sort of thing.
G6Tanuki is offline  
Old 22nd Jan 2018, 11:05 am   #7
MrBungle
Nonode
 
MrBungle's Avatar
 
Join Date: Jun 2016
Location: London, UK.
Posts: 2,553
Default Re: Rewinding slug tuned IFTs

That's an interesting idea actually. Will bear that in mind in future as well.
MrBungle is offline  
Old 22nd Jan 2018, 11:15 am   #8
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 6,397
Default Re: Rewinding slug tuned IFTs

It worked just fine as a technique for me when I wanted to retune a 10,7MHz FM IF strip down to 5.5MHz for TV sound.
G6Tanuki is offline  
Old 22nd Jan 2018, 1:21 pm   #9
G8HQP Dave
Dekatron
 
Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
Posts: 4,446
Default Re: Rewinding slug tuned IFTs

You can effectively shift the inductance up a bit by adding a parallel capacitance. Or down by adding series capacitance. It all depends on context. What was the 3.5uH needed for?
G8HQP Dave is offline  
Old 22nd Jan 2018, 2:35 pm   #10
MrBungle
Nonode
 
MrBungle's Avatar
 
Join Date: Jun 2016
Location: London, UK.
Posts: 2,553
Default Re: Rewinding slug tuned IFTs

It’s mainly a cost saving. It’s part of a narrow filter with extremely low passband ripple. If I don’t use 3.5uH then I have to combine a few capacitors as a substitute and they are quite expensive.
MrBungle is offline  
Old 24th Jan 2018, 1:46 pm   #11
MrBungle
Nonode
 
MrBungle's Avatar
 
Join Date: Jun 2016
Location: London, UK.
Posts: 2,553
Default Re: Rewinding slug tuned IFTs

Ok got my 5u3L's this morning and have tested a couple and taken averages across the board:

2u6L range from 1.7uH -> 4.2uH (sample size 6)
5u3L range from 3.7uH -> 8.1uH (sample size 5)

Looks like 2u6L will do the job here. If it doesn't meet the pass requirements, I'll swap the transformer out for a 5u3L and try again.

These were tested with a calibrated DDS and 1% 100pF mica capacitor in parallel. DDS was swept until peak was found on a scope. DDS was connected to the tank circuit with a 47k resistor so as not to completely ruin the Q of the tank and get a good peak.
MrBungle is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 10:10 am.


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 - 2018, vBulletin Solutions, Inc.
Copyright ©2002 - 2018, Paul Stenning.