KB Minuet distortion - UK Vintage Radio Repair and Restoration Discussion Forum

Ian B · 8th Apr 2009, 5:42 pm

My KB OB10 Minuet (Trader sheet 1345) sounds good for the first 15 minutes or so after switching on and then becomes distorted. R3 gets too hot to touch, but the voltages on the pins of V1 (6BE6) & V2 (6AT6) don't seem to alter from those specified. I have changed C17 and C20.

Am I barking up the wrong tree in assuming that either V1 or V2 is taking too much screen current and causing the distortion, or does R3 usually run hot? In which case I should be looking elsewhere.....

I don't have any spare valves for this set, so substitution is not an option at this stage.

Thanks in anticipation

Ian Blackbourn

Steve_P · 8th Apr 2009, 5:50 pm

Well it sounds to me like the O/P valve may be going into grid current. You could check C4, R4, R11 and R13.

Try another speaker (does not have to match, just for a test) but I would suspect V4.

Might be worth checking C15 and C16.

Cheers,

Steve P.

Ian B · 8th Apr 2009, 7:32 pm

Thanks Steve, quick reply as usual!

I'll check as you suggest.

TTFN
Ian

8th Apr 2009, 5:42 pm	#1
Ian B Hexode Join Date: May 2006 Location: Arlesey, Bedfordshire, UK. Posts: 401	KB Minuet distortion My KB OB10 Minuet (Trader sheet 1345) sounds good for the first 15 minutes or so after switching on and then becomes distorted. R3 gets too hot to touch, but the voltages on the pins of V1 (6BE6) & V2 (6AT6) don't seem to alter from those specified. I have changed C17 and C20. Am I barking up the wrong tree in assuming that either V1 or V2 is taking too much screen current and causing the distortion, or does R3 usually run hot? In which case I should be looking elsewhere..... I don't have any spare valves for this set, so substitution is not an option at this stage. Thanks in anticipation Ian Blackbourn

8th Apr 2009, 5:50 pm	#2
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: KB Minuet distortion Well it sounds to me like the O/P valve may be going into grid current. You could check C4, R4, R11 and R13. Try another speaker (does not have to match, just for a test) but I would suspect V4. Might be worth checking C15 and C16. 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...?

8th Apr 2009, 7:32 pm	#3
Ian B Hexode Join Date: May 2006 Location: Arlesey, Bedfordshire, UK. Posts: 401	Re: KB Minuet distortion Thanks Steve, quick reply as usual! I'll check as you suggest. TTFN Ian