French radio problem - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

PJL · 26th Aug 2010, 3:54 pm

The EBL3 is the IF amp. As Chris says, it could be the AGC is floating or the IF transformer is open-circuit and touching it cures the bias. It does look like there is a AGC detector bias resistor from D2 to K (your diagram does not look correct). Try measuring the resistance from the top cap to ground.

The other possibility is the finger is injecting some signal from the oscillator and there is a problem with IFT1.

humphrey · 26th Aug 2010, 7:48 pm

I think there is only two transformers-Mains and LS. All the other coils are intact. I am attempting to fix the drawing at the moment.
It seems to work correctly when the capacitor marked X is disconnected from the (inductor?) coil.
I just wonder if its something simple like an electrolytic reversed.

PJL · 27th Aug 2010, 12:57 pm

Can you do the resistance measurement from the top cap to earth.

Can you indicate in the picture where the capacitor is that you have disconnected to make it work. Everything points to it being something wrong with the IFT.

PJL · 27th Aug 2010, 1:58 pm

This is the bit I don't understand? There should only be 3 connections to the IFT, the 4th should be a wire from the top of the IFT to the top cap.

humphrey · 27th Aug 2010, 8:11 pm

The anode lead to earth is 2.16meg on EBF2
The cap that is disconnected is the one on the left as you have pictured.
There is a lot wrong with my drawing as I since discovered.
The cathode on EF9 should be linked to G3 and then to d2 (p5)on EBF2 splitting via 20ohm to earth and 200ohm to a choke and capacitor and then to the LS transformer (5 terminals) (1.5 ohms) returning to chassis.

PJL · 27th Aug 2010, 10:25 pm

2.16 is a bit high, I think it should be 500K + 1M (the black one). They have probably drifted.

Where did the capacitor go? I can't see any suitable place for it to connect to. Did you take some 'before' pictures?

humphrey · 27th Aug 2010, 10:51 pm

All the resistors are spot on and I just cleaned the contents of the can.
There is a .5M resistor in the can which gives 5 ohms more including the coil.
The reading is for the Anode connector to earth. There is a wire to the tuning coils.
Must stop now as I have a busy day tomorrow.
Thanks for your help

26th Aug 2010, 3:54 pm	#21
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: French radio problem The EBL3 is the IF amp. As Chris says, it could be the AGC is floating or the IF transformer is open-circuit and touching it cures the bias. It does look like there is a AGC detector bias resistor from D2 to K (your diagram does not look correct). Try measuring the resistance from the top cap to ground. The other possibility is the finger is injecting some signal from the oscillator and there is a problem with IFT1.

26th Aug 2010, 7:48 pm	#22
humphrey Retired Dormant Member Join Date: Aug 2008 Location: Bellac, 87. France. Posts: 357	Re: French radio problem I think there is only two transformers-Mains and LS. All the other coils are intact. I am attempting to fix the drawing at the moment. It seems to work correctly when the capacitor marked X is disconnected from the (inductor?) coil. I just wonder if its something simple like an electrolytic reversed. Last edited by humphrey; 26th Aug 2010 at 7:58 pm.

27th Aug 2010, 12:57 pm	#23
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: French radio problem Can you do the resistance measurement from the top cap to earth. Can you indicate in the picture where the capacitor is that you have disconnected to make it work. Everything points to it being something wrong with the IFT.

27th Aug 2010, 1:58 pm	#24
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: French radio problem This is the bit I don't understand? There should only be 3 connections to the IFT, the 4th should be a wire from the top of the IFT to the top cap. Attached Thumbnails

27th Aug 2010, 8:11 pm	#25
humphrey Retired Dormant Member Join Date: Aug 2008 Location: Bellac, 87. France. Posts: 357	Re: French radio problem The anode lead to earth is 2.16meg on EBF2 The cap that is disconnected is the one on the left as you have pictured. There is a lot wrong with my drawing as I since discovered. The cathode on EF9 should be linked to G3 and then to d2 (p5)on EBF2 splitting via 20ohm to earth and 200ohm to a choke and capacitor and then to the LS transformer (5 terminals) (1.5 ohms) returning to chassis.

27th Aug 2010, 10:25 pm	#26
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: French radio problem 2.16 is a bit high, I think it should be 500K + 1M (the black one). They have probably drifted. Where did the capacitor go? I can't see any suitable place for it to connect to. Did you take some 'before' pictures?

27th Aug 2010, 10:51 pm	#27
humphrey Retired Dormant Member Join Date: Aug 2008 Location: Bellac, 87. France. Posts: 357	Re: French radio problem All the resistors are spot on and I just cleaned the contents of the can. There is a .5M resistor in the can which gives 5 ohms more including the coil. The reading is for the Anode connector to earth. There is a wire to the tuning coils. Must stop now as I have a busy day tomorrow. Thanks for your help