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Old 30th Jul 2022, 10:56 am   #1
clay shooter
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Smile Denco coils substitute

It's been a couple of years since I last delved into radio, an accident at work has left me with more time on my hands than I can cope with, so I decided to build a short wave receiver, I found a circuit described by R A Penfold from about 1976 that uses The now unavailable Denco Green dp coils ( and other denco coils).
Are there any modern equivalents that can be purchased or can anyone advise me on to how to wind my own?
I'm reluctant to buy used / nos for the obvious reasons
Thanks
Martin
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Old 30th Jul 2022, 11:19 am   #2
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Default Re: Denco coils substitute

Martin - some useful information here:

http://vintageradio.me.uk/radconnav/altdenco.htm

Mike
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Old 30th Jul 2022, 11:47 am   #3
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Default Re: Denco coils substitute

They were jolly handy little coil formers - we used them by the hundredweight when I was an apprentice to L.O. Sparkes in the 50's. It is easy to wind similar coils on some suitable tube, but the biggest hurdle is arranging the B9a plugs, if you want them interchangeable.
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Old 30th Jul 2022, 12:00 pm   #4
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Default Re: Denco coils substitute

I'm not sure what 'the obvious reason' is for not buying NOS Denco coils. If it is cost, Wearite coils are usually much cheaper, but aren't plug-in.

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Old 30th Jul 2022, 12:33 pm   #5
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Angry Re: Denco coils substitute

the reason I'm reluctant to use n,o,s is that ive bought items described as this before and they have been either damaged or faulty and due to the "terms and conditions" I was unable to return or get a refund .
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Old 30th Jul 2022, 9:39 pm   #6
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Default Re: Denco coils substitute

This might not be exactly what you are looking for, but should give you an idea. I have the whole article if you are interested, but its a 10 valve radio, so its a bit complex.

Joe
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Old 30th Jul 2022, 9:57 pm   #7
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Default Re: Denco coils substitute

Quote:
Originally Posted by clay shooter View Post
the reason I'm reluctant to use n,o,s is that ive bought items described as this before and they have been either damaged or faulty and due to the "terms and conditions" I was unable to return or get a refund .
I have bought many Denco coils both used and unused without issue.

Most of the green coils I own have so few turns it hard to believe they are damaged.

Pictures may help us to understand the problems you have had?

Cheers

Mike T
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Old 31st Jul 2022, 4:01 am   #8
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Default Re: Denco coils substitute

The biggest problem i found was finding the iron dust cores.These seem to be unobtainium. Graham.
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Old 31st Jul 2022, 4:46 am   #9
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Default Re: Denco coils substitute

There are two ways to tune a coil. One is with "dust " cores, or in modern speak, ferrite cores. The other is a variable padder capacitor.

As my article described.

Joe
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Old 31st Jul 2022, 8:27 am   #10
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Default Re: Denco coils substitute

There is an alternative regarding dust cores. I used sections of old ferrite rod, glued to a brass leader screw. Attached is an example which is the input tuner for my linear amplifier. The formers are PTFE.
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Old 1st Aug 2022, 3:14 am   #11
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Default Re: Denco coils substitute

Quote:
Originally Posted by joebog1 View Post
There are two ways to tune a coil. One is with "dust " cores, or in modern speak, ferrite cores. The other is a variable padder capacitor.

As my article described.

Joe
Hi Joe,yes i have used both at times because i have never found a supply of the original threaded variety.
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Old 1st Aug 2022, 5:52 am   #12
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Default Re: Denco coils substitute

Be a little cautious, Ferrites and Iron dust mixtures are quite different beasties.

On the whole, ferrites have higher permeabilities but offer worse stability.

Ferrites can be used in inductors needing some accuracy, but they rely on the shape including a well-defined air gap in the magnetic path... EG a gapped pot core. Without the gap they are good for RF transformers and decoupling inductors where their value need not be accurate or stable.

Iron dust has effectively a lot of air gaps distributed throughout it. Complete toroid cores are popular in RF work, and have no machined gap at all. Inductance factors are reasonably reliable and the stability is good enough for VFOs.

In coil formers like the Denco ones, high frequency ferrites will not be as bad as you might expect, because of the significant air path. The air path dilutes the overall permeability of the magnetic path, and the permeability of air is very close to that of free space, and is very stable.

Unfortunately a lot of people just aren't aware of the extent of the spread of properties of these materials, they just see something grey and crunchy. I've found it to be the root cause af various people's disappointing projects. There are also mumetal dust toroids and epoxy-coated tape wound iron toroids out there waiting to catch the unwary.

David
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Old 1st Aug 2022, 6:21 am   #13
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Default Re: Denco coils substitute

Quote:
Originally Posted by joebog1 View Post
There are two ways to tune a coil. One is with "dust " cores, or in modern speak, ferrite cores. The other is a variable padder capacitor.

As my article described.

Joe
Not wishing to be pedantic, but iron dust cores and ferrite aren’t the same thing.

You can tell the difference with a file. Iron dust cores are soft and if you use a file on them, dust will come off, but a file will have no effect on ferrite. It’s quite hard to file a nick in a festive rod to snap it. (The cores in Aladdin coil formers of yesteryear were iron dust, as they were in the Ekco A22, but I’ve no idea which material Denco used).

As to Denco coils - indeed most wave-wound coils - even with a wave=winder, from my very limited experience, they’re quite difficult to replicate with a coil winder that will wave-wind. Invariably the turns of Denco, and on vintage radio RF coils, are almost always close-wound with the turns lying next to each other. Invariably there is quite a lot of air in the resultant coil. Hence, to get the required inductance the coil ends up being physically larger, and the capacitive element larger.

There are countless YouTube videos of coil winders - some quite sophisticated, but I’ve only seen a couple in which the turns are adjacent to each other, and no doubt the ‘Q’ of the coil will differ.

I don’t think there is any data about the wire gauge of Denco or the inductance of each winding, or the extent to which it varies with the adjustment of the cores. As Joe says, a trimmer is perhaps the easier option, but let’s not overlook Les’s excellent coils, the formers of which are about as close as we could get to Denco.

Of course, in QRP circles, and the home brew signal generator on Paul Stenning’s site, RF coils are often wound on ferrite toroids.
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Old 1st Aug 2022, 7:34 am   #14
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Default Re: Denco coils substitute

Thanks David,

Yes I agree with what you have said, and I do know the difference between ferrite and iron cores. When it comes to Denco ( I have never seen them in the flesh ) and many others ( Aegis in Australia for instance that I have seen and used ) The winding tension of the wire used, mostly Litz, but some higher frequency coils are plain enamelled wire, some times SCC, sometimes DCC, sometimes SC sometimes DSS, each pertaining to Q, inductance and repeatability in manufacture. Among other things. Like pure silver wire in the finest coils that I have used/seen. The coil data I put up is for a plugin coil type to be used mostly with TRF radio receivers. These coils are wound on old valve bases or coil formers that were designed specifically for purpose, BUT, not that different to an old valve base. The data is from 1949 when radio was "the king ", especially for people like us that cut our teeth on old radio like that.

With respect, Joe.
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Old 1st Aug 2022, 8:37 am   #15
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Default Re: Denco coils substitute

Quote:
Originally Posted by Radio Wrangler View Post
Be a little cautious, Ferrites and Iron dust mixtures are quite different beasties.

On the whole, ferrites have higher permeabilities but offer worse stability.

Ferrites can be used in inductors needing some accuracy, but they rely on the shape including a well-defined air gap in the magnetic path... EG a gapped pot core. Without the gap they are good for RF transformers and decoupling inductors where their value need not be accurate or stable.

Iron dust has effectively a lot of air gaps distributed throughout it. Complete toroid cores are popular in RF work, and have no machined gap at all. Inductance factors are reasonably reliable and the stability is good enough for VFOs.

In coil formers like the Denco ones, high frequency ferrites will not be as bad as you might expect, because of the significant air path. The air path dilutes the overall permeability of the magnetic path, and the permeability of air is very close to that of free space, and is very stable.

Unfortunately a lot of people just aren't aware of the extent of the spread of properties of these materials, they just see something grey and crunchy. I've found it to be the root cause af various people's disappointing projects. There are also mumetal dust toroids and epoxy-coated tape wound iron toroids out there waiting to catch the unwary.

David
A fair point - but in the example I gave, the Q was deliberately quite low, so the circuit was broad-band and stability was not a factor.
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Old 1st Aug 2022, 8:44 am   #16
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Default Re: Denco coils substitute

I'd picked up on a comment that would have confused someone not experienced in the field. I've come across quite a number of people, even in the electronics industry who thought ferrite and dust iron were the same thing. If it saves one person from problems, then I think the comment was worthwhile.

David
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Old 1st Aug 2022, 10:01 am   #17
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Default Re: Denco coils substitute

As a matter of interest, Tony Nailor of Spectrum Communications can supply both iron dust and ferrite toroids. He also supplies binocular ferrite cores as used in 'Wellgood' clone active antennas, and trimmer caps as needed when padders are used with home-brew coils an an alternative to cored coils, as referred to in Joe's posts above.

http://www.spectrumcomms.co.uk/Components.htm

Forum members may recall the enigmatic 'RF Haigh' who - for some years - was a prolific writer who wrote many articles on beautifully constructed receivers and other projects (Such as the Radio Bygones Wobbulator project). All of his receivers had hand-wound coils, and in one of the magazines he did publish details of how to go about it, but I can't recall when and which publication.

Internet is of course awash with information and publications which can be downloaded such as the one at this link.

However, for the likes of me, within a couple of pages I disappear down a rabbit hole:

https://ia904601.us.archive.org/10/i...ansformers.pdf

Looking back it's remarkable that small firms such as Osmor, Weyrad, Denco and REP were able to do all the calculations, and to manufacture such quite intricate coils. Whether or note the fine wire was actually Litz, as we assume, rather than cotton or silk covered, remains to be seen.
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Old 1st Aug 2022, 10:31 am   #18
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Default Re: Denco coils substitute

Litz wire was made in fair quantities back in the day, though it wasn't cheap. It was only later into the seventies that the price went eye-and-right-arm expensive. I modified some Denco coils and those were at least proper Litz.

David
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Old 1st Aug 2022, 11:47 am   #19
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Default Re: Denco coils substitute

I found a winding data chart for the coils, it appears that I need just a few turns of wire per winding, a friend has offered to turn some formers on his lathe so I think I will give this at try first,.
The last coil that I bought was described as NOS, but arrived with damaged winding and the silk // cotton insulation rotted away
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Old 1st Aug 2022, 12:23 pm   #20
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Default Re: Denco coils substitute

Damage is rare when the coil is supplied with data sheet in the original aluminium can.
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