Hacker Sov II rustling noise - UK Vintage Radio Repair and Restoration Discussion Forum

Radio_Dave · 3rd Nov 2010, 4:43 pm

My Hacker RP25B has a constant, rustling, noise on all wavebands, which is unaffected by volume. I've checked the electrolytics, on the amplifier board and they seem OK.

Any ideas?

TIA
David

Steve_P · 3rd Nov 2010, 4:48 pm

Clean all the buttons and connectors. Common problem.

Ground the base of TR1, then TR2 then TR4 (Amplifier board). Find out where the noise goes away. Narrow it down.

Cheers,

Steve P.

mhennessy · 3rd Nov 2010, 7:29 pm

TR1 on the amp board. These Lockfit transistors seem very unreliable in this regard - I've had this many times. TR2 might be contributing too, but TR1 always dominates. I use BC549 or BC109 to replace them, but almost any low-noise NPN amplifier will work.

I did do a scientific study on this, measuring the noise and improvements from changing the transistors. One day I might write it up. Another finding: changing the 150K resistor (R1) for a modern metal-film will improve matters by 2dB or so. Not especially audible, but interesting nonetheless...

When Steve says "ground the base", he means via a capacitor. Just in case there's any doubt

Mark

3rd Nov 2010, 4:43 pm	#1
Radio_Dave Nonode Join Date: Jun 2004 Location: Norwich, Norfolk, UK. Posts: 2,543	Hacker Sov II rustling noise My Hacker RP25B has a constant, rustling, noise on all wavebands, which is unaffected by volume. I've checked the electrolytics, on the amplifier board and they seem OK. Any ideas? TIA David

3rd Nov 2010, 4:48 pm	#2
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Hacker Sov II rustling noise Clean all the buttons and connectors. Common problem. Ground the base of TR1, then TR2 then TR4 (Amplifier board). Find out where the noise goes away. Narrow it down. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

3rd Nov 2010, 7:29 pm	#3
mhennessy Dekatron Join Date: Jul 2007 Location: Evesham, Worcestershire, UK. Posts: 4,244	Re: Hacker Sov II rustling noise TR1 on the amp board. These Lockfit transistors seem very unreliable in this regard - I've had this many times. TR2 might be contributing too, but TR1 always dominates. I use BC549 or BC109 to replace them, but almost any low-noise NPN amplifier will work. I did do a scientific study on this, measuring the noise and improvements from changing the transistors. One day I might write it up. Another finding: changing the 150K resistor (R1) for a modern metal-film will improve matters by 2dB or so. Not especially audible, but interesting nonetheless... When Steve says "ground the base", he means via a capacitor. Just in case there's any doubt Mark