Murphy A574 VHF distortion. - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Pilot Mariner · 3rd Oct 2017, 7:57 pm

Sorry for the delay in getting back, work gets in the way.
I have carried out the test as suggested in #19 and get a maximum reading at 10.9Mhz.

ukcol · 3rd Oct 2017, 11:14 pm

10.9Mhz is within 2% of 10.7 MHz. It sounds as if your IF strip is aligned about right. The discriminator still has to be correctly aligned of course.

I see there is a 3k preset in the detector which is set for optimum AM rejection. If that pot has a broken track it would cause distortion, so its worth checking.

EDIT: I have just realised that you would have no voltage at all across C54 (the voltage you have just looked at to check the alignment) if the 3k preset was open circuit, so you can safely ignore the last sentence above.

3rd Oct 2017, 7:57 pm	#21
Pilot Mariner Hexode Join Date: Jun 2003 Location: Burntwood, Staffordshire, UK or Kabaty in Warsaw Poland. Posts: 438	Re: Murphy A574 VHF distortion. Sorry for the delay in getting back, work gets in the way. I have carried out the test as suggested in #19 and get a maximum reading at 10.9Mhz.

3rd Oct 2017, 11:14 pm	#22
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: Murphy A574 VHF distortion. 10.9Mhz is within 2% of 10.7 MHz. It sounds as if your IF strip is aligned about right. The discriminator still has to be correctly aligned of course. I see there is a 3k preset in the detector which is set for optimum AM rejection. If that pot has a broken track it would cause distortion, so its worth checking. EDIT: I have just realised that you would have no voltage at all across C54 (the voltage you have just looked at to check the alignment) if the 3k preset was open circuit, so you can safely ignore the last sentence above. Last edited by ukcol; 3rd Oct 2017 at 11:42 pm.