UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Horrid intermittent on Transistor Black Box 1004

frsimen · 20th Dec 2011, 8:59 pm

Andy,

These feedback circuits are always a problem to sort out. You could try breaking the feedback loop by disconnecting R27 from VT7's collector. If you connect R27 to the centre of a potential divider made of two 470 ohm or so resistors connected in series across the supply, the voltages around VT2 ought to return to near normal. It may then be easier to establish what the problem really is.

Paula

20th Dec 2011, 8:59 pm	#11
frsimen Heptode Join Date: Jan 2011 Location: Croydon, London, UK. Posts: 773	Re: Horrid intermittent on Transistor Black Box 1004 Andy, These feedback circuits are always a problem to sort out. You could try breaking the feedback loop by disconnecting R27 from VT7's collector. If you connect R27 to the centre of a potential divider made of two 470 ohm or so resistors connected in series across the supply, the voltages around VT2 ought to return to near normal. It may then be easier to establish what the problem really is. Paula