UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

Silicon · 22nd Apr 2017, 11:12 pm

If I understand the previous posts, you have disconnected the 'top' of the volume control from IFT2.

However IF voltages are still present at both diodes in V3.

A small signal may be capacitively coupled from these diode anodes to the cathode of V3.

V3 may be operating in grounded grid mode and passing a small fixed volume signal to the audio output stage.

If you temporarily connect a 0.1uF capacitor from chassis to each diode anode (pin 5 and 6) it may reduce the volume and confirm the source of the signal.

22nd Apr 2017, 11:12 pm	#15
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,162	Re: Bush DAC 90A Conversion If I understand the previous posts, you have disconnected the 'top' of the volume control from IFT2. However IF voltages are still present at both diodes in V3. A small signal may be capacitively coupled from these diode anodes to the cathode of V3. V3 may be operating in grounded grid mode and passing a small fixed volume signal to the audio output stage. If you temporarily connect a 0.1uF capacitor from chassis to each diode anode (pin 5 and 6) it may reduce the volume and confirm the source of the signal.