UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Improving Selectivity In Vintage Receivers

Bazz4CQJ · 2nd Jan 2023, 5:11 am

I’ve measured the resistance of the coils. I used a Unit UT30B DMM (which is not pulsed) and I checked it against my Avo8 on a 10R 0.5% resistor. The DMM measured the resistor at 10.0 and the Avo at about 10.1R.

My mixer transformer measured 8.4 primary and 7.2 secondary. The data from Lawrence says 7.3R on both sides.

1.2mH needs 102pF to resonate at 455kHz, and 1.5mH needs ~81pF. So on the secondary, with the two fixed caps and the compression trimmer and all the rest of it, both L values look viable.

The data may not be as consistent as I suppose we would like it to be, but we are looking at components which are ~80 years old. War-time tolerances were probably relaxed.

B

2nd Jan 2023, 5:11 am	#92
Bazz4CQJ Dekatron Join Date: Apr 2009 Location: Oxfordshire, UK. Posts: 4,934	Re: Improving Selectivity In Vintage Receivers I’ve measured the resistance of the coils. I used a Unit UT30B DMM (which is not pulsed) and I checked it against my Avo8 on a 10R 0.5% resistor. The DMM measured the resistor at 10.0 and the Avo at about 10.1R. My mixer transformer measured 8.4 primary and 7.2 secondary. The data from Lawrence says 7.3R on both sides. 1.2mH needs 102pF to resonate at 455kHz, and 1.5mH needs ~81pF. So on the secondary, with the two fixed caps and the compression trimmer and all the rest of it, both L values look viable. The data may not be as consistent as I suppose we would like it to be, but we are looking at components which are ~80 years old. War-time tolerances were probably relaxed. B __________________ Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch.