Hi,
I have in my possession a perfectly functioning amplifier from the early 1980s. It uses discrete transistors for the finals and I need to determine the proper procedure to bias the output stage accurately.
Society has turned its back on this type of unit, deciding it is 'unfit' for HiFi reproduction. Hence, no literature is available.
In its present state, it sounds pretty nice on efficient bookshelf speakers.
I would like to dial in the exact standing current per output pair....Variable resistors on each channel are present however I do not know which testpoints to measure.
Thank you in advance.
I have in my possession a perfectly functioning amplifier from the early 1980s. It uses discrete transistors for the finals and I need to determine the proper procedure to bias the output stage accurately.
Society has turned its back on this type of unit, deciding it is 'unfit' for HiFi reproduction. Hence, no literature is available.
In its present state, it sounds pretty nice on efficient bookshelf speakers.
I would like to dial in the exact standing current per output pair....Variable resistors on each channel are present however I do not know which testpoints to measure.
Thank you in advance.
Measure across one of the emmiter load resistors when no signal is applied. The quiescent current can be between 3 and 12mAmps.
Ohms Law will give you the correct voltage across the resistor.
Personally I prefer nearer 3mA as there, in my view, is no crossover distortion at that point and any more current turns it into a class AB and it may run warm/hot.
Ohms Law will give you the correct voltage across the resistor.
Personally I prefer nearer 3mA as there, in my view, is no crossover distortion at that point and any more current turns it into a class AB and it may run warm/hot.
Why mess with it if it sounds pretty nice.
Unless you have a very low bias state (ie: xover distortion) you will gain nothing by twiddling with it.
(oops I slipped & dropped my .... in the amp with it on)
Just a thought, mind you.
Unless you have a very low bias state (ie: xover distortion) you will gain nothing by twiddling with it.
(oops I slipped & dropped my .... in the amp with it on)
Just a thought, mind you.
Hello,
This amp's finals uses one Samsung KSC and one Samsung KSA transistor per channel.
One side has VR setting range of 0 to 50mA and one side only has 0 to 15mA range.
I have cleaned out the VRs with Deoxit and they are stable and usable.
What value would be best suited to normal operation, considering the two channels have differing minimum/maximum bias ranges?
I am more used to tube equipment. The standing DC voltage at both sides' speaker outputs is equal at about 10mV now.
This amp's finals uses one Samsung KSC and one Samsung KSA transistor per channel.
One side has VR setting range of 0 to 50mA and one side only has 0 to 15mA range.
I have cleaned out the VRs with Deoxit and they are stable and usable.
What value would be best suited to normal operation, considering the two channels have differing minimum/maximum bias ranges?
I am more used to tube equipment. The standing DC voltage at both sides' speaker outputs is equal at about 10mV now.
- Status
- Not open for further replies.