Bush SRP 41 Amp issue - UK Vintage Radio Repair and Restoration Discussion Forum

plaka78 · 25th Jul 2017, 7:19 pm

I have restored this record player, On soak test I could see wisps of smoke, The output pair gets very hot. I have change all Capacitor and Resistors which made no difference, I then change the AD161 AD162 with some that I know are serviceable again made no difference, I checked the two Pots on the board and can’t see anything wrong with them, There is no distortion on the sound when its starts cooking! And the midway bias seem correct as it half the supply voltage. The only 3 things that I have not changed is the two small signal transistors and the driver transistor. If anyone got any ideas or a circuit diagram would be a great help.
The fault is also the same with zero volume setting

plaka78 · 25th Jul 2017, 7:57 pm

I gave it some thought! It had to be bias problem that sets sets the quiescent and the fact there was on distortion. Removed crossover bias pot (50 ohm) and replaced it with a 22 ohm resistor and now it run cool with clean sound. I could kick myself as I should known better!!

25th Jul 2017, 7:19 pm	#1
plaka78 Pentode Join Date: Jul 2007 Location: Salisbury, Wiltshire, UK. Posts: 174	Bush SRP 41 Amp issue I have restored this record player, On soak test I could see wisps of smoke, The output pair gets very hot. I have change all Capacitor and Resistors which made no difference, I then change the AD161 AD162 with some that I know are serviceable again made no difference, I checked the two Pots on the board and can’t see anything wrong with them, There is no distortion on the sound when its starts cooking! And the midway bias seem correct as it half the supply voltage. The only 3 things that I have not changed is the two small signal transistors and the driver transistor. If anyone got any ideas or a circuit diagram would be a great help. The fault is also the same with zero volume setting Attached Thumbnails

25th Jul 2017, 7:57 pm	#2
plaka78 Pentode Join Date: Jul 2007 Location: Salisbury, Wiltshire, UK. Posts: 174	Re: Bush SRP 41 Amp issue I gave it some thought! It had to be bias problem that sets sets the quiescent and the fact there was on distortion. Removed crossover bias pot (50 ohm) and replaced it with a 22 ohm resistor and now it run cool with clean sound. I could kick myself as I should known better!!