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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 30th Jul 2011, 11:00 pm   #1
Mixtel0
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Default Substituting Wearite "P" coils

I'm considering winding a pair of substitutes for the PA2 and PHF2. I have the inductance values (from the data sheet) so that's ok. However, the data sheet says that the specs of them are the same, but the PHF2 is a HF transformer. How is that different? Is it the coupling between the windings that varies? I don't have any originals (or even decent pictures) to get any sort of visual comparison. Can anyone help?

- Mick
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Old 31st Jul 2011, 4:18 pm   #2
Ed_Dinning
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Default Re: Substituting Wearite "P" coils

Hi Mick, looking a my Wearite catalogue it appears that both windings are the same size and inductance on the HF coil (so either could b used for tuning as it has the correct inductance).
The PA coil has the larger winding tuned (coupled to the valve grid) and the smaller winding un-tuned and connected to the aerial. This in theory gives a voltage gain from the aerial signal and some impedance maching.
The HF transformer is simply a 1::1 coupling.


Ed
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Old 31st Jul 2011, 7:46 pm   #3
Mixtel0
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Default Re: Substituting Wearite "P" coils

Many thanks Ed. I've got somewhere to start now!
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Old 31st Jul 2011, 9:23 pm   #4
Ed_Dinning
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Default Re: Substituting Wearite "P" coils

Hi Mick, if you can wait until Nov you may be able to find something similar at the Golbourne meeting; coils from 40's and 50's sets work well.

Ed
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Old 31st Jul 2011, 11:27 pm   #5
Mixtel0
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Default Re: Substituting Wearite "P" coils

When/where is that Ed? I'll be at the Llandudno radio rally 29th/30th October and for most of the following week. I bet it clashes...

I'm thinking of winding these on plastic tube. I have some 0.6" but it may make things a bit easier if I go for 25mm conduit. We have loads of it at work & I can have scraps for free. I've also considered winding on glued brown paper formers. Those would look nice and "antique"! I'm not trying to get them looking like the Wearite coils really, but I'd like them to be electronic equivalents where it really matters.

- Mick
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Old 1st Aug 2011, 9:13 am   #6
neon indicator
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Default Re: Substituting Wearite "P" coils

Larger diameter = less turns.
Plastic better than card or paper. You can always spray it 1st.

I use a strip of double sided sticky tape on the tube for coils with fine wire.
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Old 1st Aug 2011, 9:15 pm   #7
Ed_Dinning
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Default Re: Substituting Wearite "P" coils

For use at low frequencies the plastic conduit should be OK; however, many of these plastics are very lossy at higher frequencies and can leadto a substantial loss of Q due to their high relative permitivitty (Er). This manifests itself as an increase of stray capacity.

Glass works pretty well, viz the Philips superinductance sets, but air is better, hence there were ribs fitted to the Philips sets to space the wire away from the body of the former.
The weatire coils were originally wound on impregnated paper, later units were on polystyrene moulded formers. This was to allow a screw thread up the middle for a dudt core.
If you are interested there are several books available on the web detailing the design of RF coils.
Golbourne is on Sun 2 Nov I think. See me there if you want a teach-in on coils and transformers.

Ed
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