Wanted hf coil - UK Vintage Radio Repair and Restoration Discussion Forum

vinrads · 20th Jan 2021, 6:36 pm

This is for a Philips 940 trf radio the HF coil/tx is o/c the service manual gives it at 15k ohm .

Bazz4CQJ · 20th Jan 2021, 9:40 pm

I suspect that the original will be very hard to find, but I'd guess from the circuit (a larger area of the circuit would be helpful) that it's a combined anode resistor and radio frequency choke (RFC).

If that guess is correct, then wiring in a 15k resistor is series with a 2.5mH inductor might get things going. There's hardly any current flowing so a miniature inductor will cost next to nothing.

Hopefully, others could confirm?

B

vinrads · 20th Jan 2021, 10:48 pm

Thanks Bazz yes it is the ht and rf choke ,feed to the detector ,I have it working using a interstage tx , I noticed different coils alter the audio quality, the original is in the freezer, I have always heated the capacitor blocks to remove the innards ,a bit messy though , Mick.

Bazz4CQJ · 21st Jan 2021, 12:37 am

How does the freezer help put?

B

Ed_Dinning · 21st Jan 2021, 9:00 am

Hi, freezer is a good way to be able to remove pitch as it makes it very brittle. It can still fly everywhere when chipped off though.

A choke and / or resistor were my thoughts as well but not enought schematic visible to be certain. Within reason the choke can be as large as you like (economics probably dictated its size in production). Then adjust series resistor to get voltages correct, consistent with reasonable sound.
In use the choke may even have been wound with resistance wire .

Ed

vinrads · 21st Jan 2021, 9:35 am

There is nothing to be gained by showing more of the cct ,HT is fed to the bottom of the choke, one of my jobs today will to remove the choke from pitch filled box, and hope the break is accessible , well ! you never know,

Mick.

Ed_Dinning · 21st Jan 2021, 10:56 am

Hi Mick, I may have some suitable chokes if you need one. The old style wound as several "piles" will probably work fine

Ed

vinrads · 21st Jan 2021, 3:29 pm

Hi Ed ,I have the set working using a push/pull driver tx secondary windings, the two coils in series gives 11.6k I have had the tx a long time ,something tells me if I fit it I will need one in the near future, so I would be interested in your offer can you let me know the dimensions please as I would like it to fit in the original place. Mick.

Ed_Dinning · 21st Jan 2021, 4:06 pm

Hi Mick if you can post a picture when extracted and approx size I'll see what in my collection matches up.
Any idea of its max current rating?

Ed

vinrads · 21st Jan 2021, 5:26 pm

Hi Ed to fit inside the original screened box it needs to be 53mmx 43mm x40 mm, otherwise 65mmx 50mmx 55mm then I will have to make a box for it , thanks ,ps current les than 1ma about 0.75ma Mick.

Ed_Dinning · 21st Jan 2021, 7:30 pm

Hi Mick, 2 types here as shown below, both about 40mm long and 15 dia
The one out of the can has fixing bolts and is 120R, the wire ended one is 12R

Yours for the postage

Ed

vinrads · 21st Jan 2021, 8:12 pm

Hi Ed thanks for that but I think it needs to have some iron in it ,I tried something similar to what you have there, didn't work. Mick.

vinrads · 22nd Jan 2021, 1:25 pm

Picture of the choke, the wire is very thin 0.06mm Mick.

20th Jan 2021, 6:36 pm	#1
vinrads Nonode Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 2,645	Wanted hf coil This is for a Philips 940 trf radio the HF coil/tx is o/c the service manual gives it at 15k ohm . Attached Thumbnails

20th Jan 2021, 9:40 pm	#2
Bazz4CQJ Dekatron Join Date: Apr 2009 Location: Oxfordshire, UK. Posts: 3,159	Re: Wanted hf coil I suspect that the original will be very hard to find, but I'd guess from the circuit (a larger area of the circuit would be helpful) that it's a combined anode resistor and radio frequency choke (RFC). If that guess is correct, then wiring in a 15k resistor is series with a 2.5mH inductor might get things going. There's hardly any current flowing so a miniature inductor will cost next to nothing. Hopefully, others could confirm? B __________________ Data beats opinions most times... that's my opinion, though I have no data on that.

20th Jan 2021, 10:48 pm	#3
vinrads Nonode Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 2,645	Re: Wanted hf coil Thanks Bazz yes it is the ht and rf choke ,feed to the detector ,I have it working using a interstage tx , I noticed different coils alter the audio quality, the original is in the freezer, I have always heated the capacitor blocks to remove the innards ,a bit messy though , Mick.

21st Jan 2021, 12:37 am	#4
Bazz4CQJ Dekatron Join Date: Apr 2009 Location: Oxfordshire, UK. Posts: 3,159	Re: Wanted hf coil How does the freezer help put? B __________________ Data beats opinions most times... that's my opinion, though I have no data on that.

21st Jan 2021, 9:00 am	#5
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 6,571	Re: Wanted hf coil Hi, freezer is a good way to be able to remove pitch as it makes it very brittle. It can still fly everywhere when chipped off though. A choke and / or resistor were my thoughts as well but not enought schematic visible to be certain. Within reason the choke can be as large as you like (economics probably dictated its size in production). Then adjust series resistor to get voltages correct, consistent with reasonable sound. In use the choke may even have been wound with resistance wire . Ed

21st Jan 2021, 9:35 am	#6
vinrads Nonode Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 2,645	Re: Wanted hf coil There is nothing to be gained by showing more of the cct ,HT is fed to the bottom of the choke, one of my jobs today will to remove the choke from pitch filled box, and hope the break is accessible , well ! you never know, Mick.

21st Jan 2021, 10:56 am	#7
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 6,571	Re: Wanted hf coil Hi Mick, I may have some suitable chokes if you need one. The old style wound as several "piles" will probably work fine Ed

21st Jan 2021, 3:29 pm	#8
vinrads Nonode Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 2,645	Re: Wanted hf coil Hi Ed ,I have the set working using a push/pull driver tx secondary windings, the two coils in series gives 11.6k I have had the tx a long time ,something tells me if I fit it I will need one in the near future, so I would be interested in your offer can you let me know the dimensions please as I would like it to fit in the original place. Mick.

21st Jan 2021, 4:06 pm	#9
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 6,571	Re: Wanted hf coil Hi Mick if you can post a picture when extracted and approx size I'll see what in my collection matches up. Any idea of its max current rating? Ed

21st Jan 2021, 5:26 pm	#10
vinrads Nonode Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 2,645	Re: Wanted hf coil Hi Ed to fit inside the original screened box it needs to be 53mmx 43mm x40 mm, otherwise 65mmx 50mmx 55mm then I will have to make a box for it , thanks ,ps current les than 1ma about 0.75ma Mick. Last edited by vinrads; 21st Jan 2021 at 5:45 pm.

21st Jan 2021, 7:30 pm	#11
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 6,571	Re: Wanted hf coil Hi Mick, 2 types here as shown below, both about 40mm long and 15 dia The one out of the can has fixing bolts and is 120R, the wire ended one is 12R Yours for the postage Ed Attached Thumbnails

21st Jan 2021, 8:12 pm	#12
vinrads Nonode Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 2,645	Re: Wanted hf coil Hi Ed thanks for that but I think it needs to have some iron in it ,I tried something similar to what you have there, didn't work. Mick.

22nd Jan 2021, 1:25 pm	#13
vinrads Nonode Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 2,645	Re: Wanted hf coil Picture of the choke, the wire is very thin 0.06mm Mick. Attached Thumbnails