Philips D1040 IF transformer bodge - UK Vintage Radio Repair and Restoration Discussion Forum

TonyDuell · 15th Aug 2020, 4:35 pm

This might amuse some of you.

The Philips D1040 is a portable MW/LW set. The PCB has clearly come from a pocket radio (cutout for the speaker and on-board volume control), it's mounted in a larger cabinet with the volume control on 5 wires, a slightly larger speaker, etc.

Electronically it's conventional (frequency changer, 2 IF amplifier stages, diode detector, audio driver, push-pull output).

Mine was receiving nothing, but touching the slider of the volume control showed the audio side was working. Checking transistor voltages showed that there was nothing on the base of the second IF amplifier. And that was because the secondary winding of the IF transformer was open-circuit (one end goes to the bias network, the other to the transistor base).

Alas resoldering the ends didn't help. The primary was wound over the secondary so re-winding it would be a pair. But the primary was the only tuned winding, and it was still good.]

Since I don't have such IF transformers in stock I did a bodge that goes back many years. Convert the circuit to RC coupling. I put a sutable resistor (220k) across the open-circuit secondary so supply the bias voltage. And a capacitor (few hundred pF) from the collector of the first IF amplifier to the base of the second.

Amazingly it worked first time. I guess it's not as selective as it should be but at least I can receive something...

vinrads · 15th Aug 2020, 4:42 pm

I bet it's not much different , the det tx is usually pretty flat when re aligning, I consider it a good stand by , until a tx comes along , Mick.

TonyDuell · 15th Aug 2020, 4:54 pm

It's certainly better than no reception at all...

And as I just soldered the extra components to the track side of the PCB, I can remove them if I ever find a suitable IFT.

15th Aug 2020, 4:35 pm	#1
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,219	Philips D1040 IF transformer bodge This might amuse some of you. The Philips D1040 is a portable MW/LW set. The PCB has clearly come from a pocket radio (cutout for the speaker and on-board volume control), it's mounted in a larger cabinet with the volume control on 5 wires, a slightly larger speaker, etc. Electronically it's conventional (frequency changer, 2 IF amplifier stages, diode detector, audio driver, push-pull output). Mine was receiving nothing, but touching the slider of the volume control showed the audio side was working. Checking transistor voltages showed that there was nothing on the base of the second IF amplifier. And that was because the secondary winding of the IF transformer was open-circuit (one end goes to the bias network, the other to the transistor base). Alas resoldering the ends didn't help. The primary was wound over the secondary so re-winding it would be a pair. But the primary was the only tuned winding, and it was still good.] Since I don't have such IF transformers in stock I did a bodge that goes back many years. Convert the circuit to RC coupling. I put a sutable resistor (220k) across the open-circuit secondary so supply the bias voltage. And a capacitor (few hundred pF) from the collector of the first IF amplifier to the base of the second. Amazingly it worked first time. I guess it's not as selective as it should be but at least I can receive something...

15th Aug 2020, 4:42 pm	#2
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,766	Re: Philips D1040 IF transformer bodge I bet it's not much different , the det tx is usually pretty flat when re aligning, I consider it a good stand by , until a tx comes along , Mick.

15th Aug 2020, 4:54 pm	#3
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,219	Re: Philips D1040 IF transformer bodge It's certainly better than no reception at all... And as I just soldered the extra components to the track side of the PCB, I can remove them if I ever find a suitable IFT.