Homemade Denco Coils - UK Vintage Radio Repair and Restoration Discussion Forum

jim_jobe · 10th Oct 2007, 6:35 pm

Attached is a photo of a couple of Range 4 Denco Homemade coils. Don't be fooled by the colour - one is Blue and the other Green, Range 4, but Yellow was the only colour tubing available! I used a nylon nut and bolt with a ferrite bead Araldited to the end of the bolt for tuning. The tubing is 3/8 in. dia that I just happened to have a piece of but I've made similar coils using old pen barrels,etc. If anyone can point me to a source of suitable coloured tubing I'd be very grateful.
I've worked out the winding details for all Denco coils -DP and Transistor - in the 3,4 & 5 Ranges. If you'd like a copy send me your email address and I'll send it as an attachment. I've scanned it but it uses too much memory to post here.

For Range 4, the main winding (Denco pins 1 & 6) is 15.5 Turns; Aerial Coupling,(Pins 8 & 9) 4 Turns above main winding; Base Bias/Output Coupling (Pins 5 & 7), 2 Turns over bottom of main winding; Green Feedback,(Pins 3 & 4),8 Turns on top of main winding. All 30 SWG.
NB: The lower pin number in each case is the start of that winding.

Hope this is useful,
Jim

paulsherwin · 10th Oct 2007, 6:39 pm

Quote:

Originally Posted by jim_jobe

The tubing is 3/8 in. dia that I just happened to have a piece of but I've made similar coils using old pen barrels,etc. If anyone can point me to a source of suitable coloured tubing I'd be very grateful.

Jim, doesn't the plastic tubing reduce the Q of the coils? What are good and bad materials to use?

Paul

Ed_Dinning · 10th Oct 2007, 6:59 pm

Hi Jim, some of the hobby shops and larger B&Q's have "metals bars" and usually asociated with these is a "plastics bar". They are a collection of stock sizes that are not easy to find for the average hobbyist at moderately high prices.
Try looking at magazines such as "Model Engineers Workshop" & "Model Engineer". There should be suppliers in there.
For a design of TV22 LOPT I have used plastic conduit and waste pipe. This seems to work well but the frequencies are quite low.

For higher frequency work you need to look for a material with low Er (permitivitty) and ideally a low loss factor.
Glass tubing would make a good former amd glass glues are readily available. Cardboard tubes would also work if well baked and varnished.
I believe RS now do a range of suitable Tufnol tubes and are no longer trade only.

The other dodge is to air-space the turns from the former with thin strips of wood or similar at, say, 60 Deg intervals.

Get experimenting, Ed

OErjan_S · 11th Oct 2007, 9:44 am

Sorry for barging in here.

paulsherwin

Polystyrene (stuff sold for odel cars and planes mostly), poypropylene and PEHD are all good for HF coils.
Polystyrene are usually labeled PS or Styrene.
I have used them all making coils with Q well above 700 at 1.5Mhz, so should be ok for most applications.

uneven winding/s and bad solder joints together with any overlapping turns are MUCH higher impact on Q than exact plastic used.
even sharp "points" of solder sticking out start mattering aroud 2Mhz (if, like me, you are trying to go over 1200 in Q at 1500kHz anyway).

Another Q factor not to be neglected is spacing, 1/2-1 wiredia spacing between turns raise Q quite a bit (eddycurrents and proximityeffects lessen with square of distance)

exact type of ferite also as a great impact on Q.

also the glue used to hold the windings matter, beeswax and parafinwax work well, styrene diislved in thinner (coil goop) better, epoxy and hotglue are NOT good for Q and neither is contact cement, superglue or polyurethane.

To be fair, not many coils need to be 1000+Q.

jim_jobe · 11th Oct 2007, 10:45 am

I try to avoid putting glue onto the windings themselves,only on the start and finish if necessary. The only former material I've had any doubts about is grey coloured waste pipe but I've never actually tried measuring Q directly. Coincidentally, I was in Smith's yesterday looking for PW and came across the October issue of Everyday Electronics, October issue. They are doing a constructional article on a Q-Factor and Inductance meter using an AT90S2313 Microcontroller - Ranges are 200nH -10mH and Q-factor 1-120 autoranging at frequencies up to 20MHz - so I might have a go at that if the bits aren't too expensive.
Q of 1000+ sounds pretty awesome to me - I take my hat off to you OErjan!
I have used glass rod and glass tubing in the past Ed and got good results but they didn't look as good(!!!) as plastics. You've reminded me that I have a recipe for glass glue somewhere in an old UNESCO Handbook. I'll see if I can dig that out.
Cheers,
Jim

OErjan_S · 11th Oct 2007, 2:27 pm

Actualy most plastics are POOR coil formers, and paper is even worse (no matter baking and sealing). PEHD, PS and PP are all found in food and medicine containers, should be plenty of suitable things around.
avoid black and red/orange plastics they can contain pigments that may ruin Q (iron oxide or carbon=>black-->grey). clear and white usually ok.

any glue anywhere on the wire (In the particular part of the circuitt to be exact) will affect Q.
Any solder anywhere (any joints, splices...), shortest lead possible,
minding wireplacement, no wire ends sticking out...
same goes for whole system, no one component must be overlooked when going to HIGH Q's.
I admit that the 1000+Q is unloaded tank Q, loaded Q is lower, MUCH lower.
how much lowr depend among other things on antenna/ground and detector/phones and all
the impedancematching and tuning needed for them...
I usually keep things selective enough to tune 40m ham band.

Rant and off topic below

yes I tune 40m band on a crystalset, by accident i found that local powerline QRM act
as a random BFO allowing me to receive CW on my crystalsets, sadly the stability is far from acceptable

must talk to powercompany so they stabilize the output

Actually the QRM is likely going away now, maintenance crew is replacing insulators and
some other things here as I write

.
Suspect use of a tiny 1 FET VXO, inductively coupled to my set, would be needed
for CW from now on, should at least allow me better stability.

jim_jobe · 13th Oct 2007, 11:07 am

Sounds fascinating - what are you using for a detector on your Crystal Set - a Schottky Diode?
Jim

Eric_Harvie · 16th Oct 2007, 4:13 pm

A few thoughts.
High Density Polythene HDPE, Low Density Polythene LDPE, Polythene PP, and PVC are all pretty close as very good coil formers.
Optimize L : D for individual radio--coil may even become "square".
White thin walled plastics come out best.

paulsherwin · 16th Oct 2007, 4:54 pm

Quote:

Originally Posted by Eric_Harvie

High Density Polythene HDPE, Low Density Polythene LDPE, Polythene PP, and PVC are all pretty close as very good coil formers.

A good coil former I've just thought of is old 35mm plastic film containers. These are mostly HDPE (I've just checked - it's stamped on the bottom

). I use these to store harvested flower and shrub seeds for the next season.

If you walk into your local high street film processors (Snappy Snaps type places) and ask nicely, they will give you carrier bags full of the things. This is still true now despite the rise of digital photography.

Paul

dave walsh · 16th Oct 2007, 9:54 pm

Given all the erudite tech info on plastics I was beginning to wonder what WOULD be a suitable coil former material. In view of previous threads about
trying to re-start Denco any "home brew " solution could be invaluable!
As a slight aside and in view of Paul's excellent film can suggestion, this has definetely been done before with good results-not re Denco but somewhere else. I know this because a couple of years ago the Guardian letters page developed one of it's ongoing subject threads which go on day after day sometimes. A previous one had been Dylan/Martin Carthy circa 1962. This one was how to use "used" plastic film cannisters? [I'm sure seeds got a mention Paul].After what seemed forever I finally wrote in to say that electronic enthusiasts wound coils on them [most suggestions involved things in them]. Ironically, after dozens of suggestions, I suspect that mine was the only one not printed! I think I saw this coil usage in an RSGB Tech Topics but I can't be sure.Dave

llama · 16th Oct 2007, 10:48 pm

"re-start Denco" is interesting. I handed most of my old Denco stuff to Ron (propreitor of Burcarts in Clacton) as he was interested in collecting a museum for Denco. His family originated Denco. So I guess he still owns the name but may be interested in some collaboration. Sorry I haven't expressed this clearly - it's getting late...
Graham

OErjan_S · 17th Oct 2007, 12:36 am

jim_jobe
Any windinginfo on tose coils would be nice. always good to have such things on the shelf.

as for my set.
I use FO215 Germanium, it has good performance at low sigal levels (on high impedance high Q sets), also Agilent 5082-2835, sadly that can give distorted sound...
also as suspected 95% of the RF disturbance is now gone

as for CW and ssb, I broke down and made a tiny vxo, could not find exact circuit online but a similar is here.
http://www.southgatearc.org/qrp/vxo.htm
ust built it and put inside a filmcan with 3 turn round can as loop antenna. easy to couple to any coil and easy to vary coupling by rotating can or move it around on table.

Eric_Harvie,
PVC? as far as I know it will drop Q with 15%+ compared to the ones I mentioned, plexiglas (acrylic) and lexan (polycarbonate) are really bad.

jim_jobe · 17th Oct 2007, 10:32 am

I've used film containers a few times in the past and had good results with them. I have quite a big stock of them as I happen to be the beetle recorder for this area and people are always leaving beasties to be identified on my doorstop, usually in a film container!
A thought though - with digital photography fast becoming the norm will the supply of film containers dry up completely - will they sell for enormous amounts on eBay?? I should hang on to them gents!
Jim

paulsherwin · 17th Oct 2007, 10:48 am

Quote:

Originally Posted by jim_jobe

I've used film containers a few times in the past and had good results with them. I have quite a big stock of them as I happen to be the beetle recorder for this area and people are always leaving beasties to be identified on my doorstop, usually in a film container!
A thought though - with digital photography fast becoming the norm will the supply of film containers dry up completely - will they sell for enormous amounts on eBay?? I should hang on to them gents!
Jim

There is still quite a lot of 35mm film being used, largely by technophobes who don't want to get up to speed with digital but also by high end photographers and people with good 35mm cameras they don't want to replace. There are fewer high street rapid processors than there used to be, but the remaining ones still seem to be doing lots of onsite processing and are happy to give the containers away.

Eventually the high street operatore will stop doing onsite processing and it will be more difficult to find the containers. I have a stock of about a hundred

Paul

Wilko · 26th Jan 2008, 10:24 pm

I've also used film canisters for coils. The most successful former for air-wound coils I've used was the plastic tubing that my work organisation buys replacement hacksaw blades in. I suspect it might be PVC or Polypropelene. I wound everything from pile-wound LW and MW coils to shortwave coils on this tubing and they all worked really well. I also have a quantity of what look like little plastic vials with a plastic stopper. I'm going to give these a try.

10th Oct 2007, 6:35 pm	#1
jim_jobe Heptode Join Date: Nov 2004 Location: Ripon, N.Yorkshire, UK. Posts: 782	Homemade Denco Coils Attached is a photo of a couple of Range 4 Denco Homemade coils. Don't be fooled by the colour - one is Blue and the other Green, Range 4, but Yellow was the only colour tubing available! I used a nylon nut and bolt with a ferrite bead Araldited to the end of the bolt for tuning. The tubing is 3/8 in. dia that I just happened to have a piece of but I've made similar coils using old pen barrels,etc. If anyone can point me to a source of suitable coloured tubing I'd be very grateful. I've worked out the winding details for all Denco coils -DP and Transistor - in the 3,4 & 5 Ranges. If you'd like a copy send me your email address and I'll send it as an attachment. I've scanned it but it uses too much memory to post here. For Range 4, the main winding (Denco pins 1 & 6) is 15.5 Turns; Aerial Coupling,(Pins 8 & 9) 4 Turns above main winding; Base Bias/Output Coupling (Pins 5 & 7), 2 Turns over bottom of main winding; Green Feedback,(Pins 3 & 4),8 Turns on top of main winding. All 30 SWG. NB: The lower pin number in each case is the start of that winding. Hope this is useful, Jim Attached Thumbnails

10th Oct 2007, 6:59 pm	#3
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Homemade Denco Coils Hi Jim, some of the hobby shops and larger B&Q's have "metals bars" and usually asociated with these is a "plastics bar". They are a collection of stock sizes that are not easy to find for the average hobbyist at moderately high prices. Try looking at magazines such as "Model Engineers Workshop" & "Model Engineer". There should be suppliers in there. For a design of TV22 LOPT I have used plastic conduit and waste pipe. This seems to work well but the frequencies are quite low. For higher frequency work you need to look for a material with low Er (permitivitty) and ideally a low loss factor. Glass tubing would make a good former amd glass glues are readily available. Cardboard tubes would also work if well baked and varnished. I believe RS now do a range of suitable Tufnol tubes and are no longer trade only. The other dodge is to air-space the turns from the former with thin strips of wood or similar at, say, 60 Deg intervals. Get experimenting, Ed

11th Oct 2007, 9:44 am	#4
OErjan_S Retired Dormant Member Join Date: Mar 2007 Location: Skelleftea, Sweden Posts: 250	Re: Homemade Denco Coils Sorry for barging in here. paulsherwin Polystyrene (stuff sold for odel cars and planes mostly), poypropylene and PEHD are all good for HF coils. Polystyrene are usually labeled PS or Styrene. I have used them all making coils with Q well above 700 at 1.5Mhz, so should be ok for most applications. uneven winding/s and bad solder joints together with any overlapping turns are MUCH higher impact on Q than exact plastic used. even sharp "points" of solder sticking out start mattering aroud 2Mhz (if, like me, you are trying to go over 1200 in Q at 1500kHz anyway). Another Q factor not to be neglected is spacing, 1/2-1 wiredia spacing between turns raise Q quite a bit (eddycurrents and proximityeffects lessen with square of distance) exact type of ferite also as a great impact on Q. also the glue used to hold the windings matter, beeswax and parafinwax work well, styrene diislved in thinner (coil goop) better, epoxy and hotglue are NOT good for Q and neither is contact cement, superglue or polyurethane. To be fair, not many coils need to be 1000+Q.

11th Oct 2007, 10:45 am	#5
jim_jobe Heptode Join Date: Nov 2004 Location: Ripon, N.Yorkshire, UK. Posts: 782	Re: Homemade Denco Coils I try to avoid putting glue onto the windings themselves,only on the start and finish if necessary. The only former material I've had any doubts about is grey coloured waste pipe but I've never actually tried measuring Q directly. Coincidentally, I was in Smith's yesterday looking for PW and came across the October issue of Everyday Electronics, October issue. They are doing a constructional article on a Q-Factor and Inductance meter using an AT90S2313 Microcontroller - Ranges are 200nH -10mH and Q-factor 1-120 autoranging at frequencies up to 20MHz - so I might have a go at that if the bits aren't too expensive. Q of 1000+ sounds pretty awesome to me - I take my hat off to you OErjan! I have used glass rod and glass tubing in the past Ed and got good results but they didn't look as good(!!!) as plastics. You've reminded me that I have a recipe for glass glue somewhere in an old UNESCO Handbook. I'll see if I can dig that out. Cheers, Jim

11th Oct 2007, 2:27 pm	#6
OErjan_S Retired Dormant Member Join Date: Mar 2007 Location: Skelleftea, Sweden Posts: 250	Re: Homemade Denco Coils Actualy most plastics are POOR coil formers, and paper is even worse (no matter baking and sealing). PEHD, PS and PP are all found in food and medicine containers, should be plenty of suitable things around. avoid black and red/orange plastics they can contain pigments that may ruin Q (iron oxide or carbon=>black-->grey). clear and white usually ok. any glue anywhere on the wire (In the particular part of the circuitt to be exact) will affect Q. Any solder anywhere (any joints, splices...), shortest lead possible, minding wireplacement, no wire ends sticking out... same goes for whole system, no one component must be overlooked when going to HIGH Q's. I admit that the 1000+Q is unloaded tank Q, loaded Q is lower, MUCH lower. how much lowr depend among other things on antenna/ground and detector/phones and all the impedancematching and tuning needed for them... I usually keep things selective enough to tune 40m ham band. Rant and off topic below yes I tune 40m band on a crystalset, by accident i found that local powerline QRM act as a random BFO allowing me to receive CW on my crystalsets, sadly the stability is far from acceptable must talk to powercompany so they stabilize the output Actually the QRM is likely going away now, maintenance crew is replacing insulators and some other things here as I write . Suspect use of a tiny 1 FET VXO, inductively coupled to my set, would be needed for CW from now on, should at least allow me better stability. Last edited by OErjan_S; 11th Oct 2007 at 2:34 pm.

13th Oct 2007, 11:07 am	#7
jim_jobe Heptode Join Date: Nov 2004 Location: Ripon, N.Yorkshire, UK. Posts: 782	Re: Homemade Denco Coils Sounds fascinating - what are you using for a detector on your Crystal Set - a Schottky Diode? Jim

16th Oct 2007, 4:13 pm	#8
Eric_Harvie Triode Join Date: Nov 2004 Location: Edinburgh, UK. Posts: 31	Re: Homemade Denco Coils A few thoughts. High Density Polythene HDPE, Low Density Polythene LDPE, Polythene PP, and PVC are all pretty close as very good coil formers. Optimize L : D for individual radio--coil may even become "square". White thin walled plastics come out best. __________________ I'm smiling. That should scare you.

16th Oct 2007, 9:54 pm	#10
dave walsh Dekatron Join Date: Jan 2006 Location: Ramsbottom (Nr Bury) Lancs or Bexhill (Nr Hastings) Sussex. Posts: 5,817	Re: Homemade Denco Coils Given all the erudite tech info on plastics I was beginning to wonder what WOULD be a suitable coil former material. In view of previous threads about trying to re-start Denco any "home brew " solution could be invaluable! As a slight aside and in view of Paul's excellent film can suggestion, this has definetely been done before with good results-not re Denco but somewhere else. I know this because a couple of years ago the Guardian letters page developed one of it's ongoing subject threads which go on day after day sometimes. A previous one had been Dylan/Martin Carthy circa 1962. This one was how to use "used" plastic film cannisters? [I'm sure seeds got a mention Paul].After what seemed forever I finally wrote in to say that electronic enthusiasts wound coils on them [most suggestions involved things in them]. Ironically, after dozens of suggestions, I suspect that mine was the only one not printed! I think I saw this coil usage in an RSGB Tech Topics but I can't be sure.Dave

16th Oct 2007, 10:48 pm	#11
llama Octode Join Date: Jun 2006 Location: St Osyth, Nr Clacton, Essex, UK. Posts: 1,482	Re: Homemade Denco Coils "re-start Denco" is interesting. I handed most of my old Denco stuff to Ron (propreitor of Burcarts in Clacton) as he was interested in collecting a museum for Denco. His family originated Denco. So I guess he still owns the name but may be interested in some collaboration. Sorry I haven't expressed this clearly - it's getting late... Graham

17th Oct 2007, 12:36 am	#12
OErjan_S Retired Dormant Member Join Date: Mar 2007 Location: Skelleftea, Sweden Posts: 250	Re: Homemade Denco Coils jim_jobe Any windinginfo on tose coils would be nice. always good to have such things on the shelf. as for my set. I use FO215 Germanium, it has good performance at low sigal levels (on high impedance high Q sets), also Agilent 5082-2835, sadly that can give distorted sound... also as suspected 95% of the RF disturbance is now gone as for CW and ssb, I broke down and made a tiny vxo, could not find exact circuit online but a similar is here. http://www.southgatearc.org/qrp/vxo.htm ust built it and put inside a filmcan with 3 turn round can as loop antenna. easy to couple to any coil and easy to vary coupling by rotating can or move it around on table. Eric_Harvie, PVC? as far as I know it will drop Q with 15%+ compared to the ones I mentioned, plexiglas (acrylic) and lexan (polycarbonate) are really bad.

17th Oct 2007, 10:32 am	#13
jim_jobe Heptode Join Date: Nov 2004 Location: Ripon, N.Yorkshire, UK. Posts: 782	Re: Homemade Denco Coils I've used film containers a few times in the past and had good results with them. I have quite a big stock of them as I happen to be the beetle recorder for this area and people are always leaving beasties to be identified on my doorstop, usually in a film container! A thought though - with digital photography fast becoming the norm will the supply of film containers dry up completely - will they sell for enormous amounts on eBay?? I should hang on to them gents! Jim

26th Jan 2008, 10:24 pm	#15
Wilko Retired Dormant Member Join Date: Nov 2006 Location: Peterborough Posts: 1	Re: Homemade Denco Coils I've also used film canisters for coils. The most successful former for air-wound coils I've used was the plastic tubing that my work organisation buys replacement hacksaw blades in. I suspect it might be PVC or Polypropelene. I wound everything from pile-wound LW and MW coils to shortwave coils on this tubing and they all worked really well. I also have a quantity of what look like little plastic vials with a plastic stopper. I'm going to give these a try.