UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Two or three IF stage Chinese radio kits.

G8HQP Dave · 31st Dec 2016, 8:08 pm

I think R4 is 'adjust on test'. VT3 provides a bias negative feedback loop, which also biases VT2. VT2 has its emitter connected to 0V so is well turned on - well, if 0.5mA counts! VT3 has a big resistor in its emitter (the volume control) so has very low quiescent current. It is essentially an infinite impedance detector. So this set has one IF stage, not the two or three of the thread title.

The audio circuit is rather crude so good results are not to be expected.

My guess is that C5 (22nF?) is too high in capacitance, and so causing slew rate limiting. Try 10nF or even 4.7nF.

31st Dec 2016, 8:08 pm	#12
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: Two or three IF stage Chinese radio kits. I think R4 is 'adjust on test'. VT3 provides a bias negative feedback loop, which also biases VT2. VT2 has its emitter connected to 0V so is well turned on - well, if 0.5mA counts! VT3 has a big resistor in its emitter (the volume control) so has very low quiescent current. It is essentially an infinite impedance detector. So this set has one IF stage, not the two or three of the thread title. The audio circuit is rather crude so good results are not to be expected. My guess is that C5 (22nF?) is too high in capacitance, and so causing slew rate limiting. Try 10nF or even 4.7nF.