Perdio Radio PC-16 Chassis - UK Vintage Radio Repair and Restoration Discussion Forum

sonoguy · 1st Jul 2022, 12:59 pm

I have several Perdio Radios with PC-16 chassis and some similar design Sobell and McMichael models. I have recently noticed a problem which is quite peculiar on a couple of the Perdio models only - both Piccadilly models by the way. On Long Wave Radio 4 the audio is distorted; more so depending on signal strength - turning the set, the stronger the signal the worse the distortion. It is not so noticeable on MW. It seems the AGC line is not working. I've checked various components in the AGC area in both radios and not found anything wrong, except one of the chassis seems to have a modifed neutralisation circuit. In one set C17 18pF is not fitted and R4 is connected from anode of D1 to base of TR3 - soldering is original untouched. With either radio, touching with a meter probe around the base or collector of TR2 or TR3 cures the distortion. Transistor voltages seem OK. Any ideas which part of the circuit I should check next?

coopzone · 2nd Jul 2022, 9:22 pm

You mention that when you measure the voltages on the transistors the distortion stops?

This could indicates a couple of things. For example filtering caps not working properly maybe a high frequency oscillation that is throwing of the AGC and when you use the meter it effectively stops this. Worth checking the caps throughout, especially the filter ones.

Or maybe a resistor out of spec (R16 / R8) again adding the meter maybe brings the values down a little?

I have a couple of these type radios (super 7, same PCB) neither seem to have this issue.

Silicon · 3rd Jul 2022, 1:26 pm

The electrolytic capacitors would be a good place to start your search for faulty components.

The smaller value ones tend to dry out and fail.

1st Jul 2022, 12:59 pm	#1
sonoguy Triode Join Date: May 2016 Location: Walsall, West Midlands, UK. Posts: 17	Perdio Radio PC-16 Chassis I have several Perdio Radios with PC-16 chassis and some similar design Sobell and McMichael models. I have recently noticed a problem which is quite peculiar on a couple of the Perdio models only - both Piccadilly models by the way. On Long Wave Radio 4 the audio is distorted; more so depending on signal strength - turning the set, the stronger the signal the worse the distortion. It is not so noticeable on MW. It seems the AGC line is not working. I've checked various components in the AGC area in both radios and not found anything wrong, except one of the chassis seems to have a modifed neutralisation circuit. In one set C17 18pF is not fitted and R4 is connected from anode of D1 to base of TR3 - soldering is original untouched. With either radio, touching with a meter probe around the base or collector of TR2 or TR3 cures the distortion. Transistor voltages seem OK. Any ideas which part of the circuit I should check next? Attached Thumbnails

2nd Jul 2022, 9:22 pm	#2
coopzone Hexode Join Date: Jan 2018 Location: Cannock, Staffordshire, UK. Posts: 268	Re: Perdio Radio PC-16 Chassis You mention that when you measure the voltages on the transistors the distortion stops? This could indicates a couple of things. For example filtering caps not working properly maybe a high frequency oscillation that is throwing of the AGC and when you use the meter it effectively stops this. Worth checking the caps throughout, especially the filter ones. Or maybe a resistor out of spec (R16 / R8) again adding the meter maybe brings the values down a little? I have a couple of these type radios (super 7, same PCB) neither seem to have this issue.

3rd Jul 2022, 1:26 pm	#3
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,163	Re: Perdio Radio PC-16 Chassis The electrolytic capacitors would be a good place to start your search for faulty components. The smaller value ones tend to dry out and fail.