"It is a hard swing to one or the other of the rails as the feedback loop is broken."
I'm not sure I'm picturing this right.
I take off pin 6 while I'm measuring DC from both of the voltage rails?
Indeterminate values across R22 or in the voltage rails.
I'm not sure I'm picturing this right.
I take off pin 6 while I'm measuring DC from both of the voltage rails?
Indeterminate values across R22 or in the voltage rails.
DC offset is measured between ground and the amplifier output. If you are seeing different results each time then this suggests either a physical construction problem (something intermittent) or random oscillation.
On any DC coupled amplifier, any real fault normally causes the output to go toward one of the two supply rails.
On any DC coupled amplifier, any real fault normally causes the output to go toward one of the two supply rails.
Doesn't seem to be connection problem nor oscillation.
If I look at the positive and negative rails and disconnect bias, nothing happens. If I couple oscilloscope to DC, then there is difference at the positive rail but still nothing happens when I disconnect it.
How should I measure the "swing"?
If I look at the positive and negative rails and disconnect bias, nothing happens. If I couple oscilloscope to DC, then there is difference at the positive rail but still nothing happens when I disconnect it.
How should I measure the "swing"?
1. Speakers disconnected (or connect the meter to the 'B' speakers and set the front panel speaker control accordingly)
2. Input set to an unusued position (not Phono)
3. Volume control at minimum.
4. Balance in center
5. Tone controls either defeated or set to mid position
6. Set your meter to read DC, and set to a low scale (300mV scale is common) Connect directly to the Pos and Neg of the speaker terminals
7. Give the amp 10 minutes to settle. Report back...I'd like to see how healthy all these old amps are.
I did exactly like this and it still gives me multiple volts. -6V
2. Input set to an unusued position (not Phono)
3. Volume control at minimum.
4. Balance in center
5. Tone controls either defeated or set to mid position
6. Set your meter to read DC, and set to a low scale (300mV scale is common) Connect directly to the Pos and Neg of the speaker terminals
7. Give the amp 10 minutes to settle. Report back...I'd like to see how healthy all these old amps are.
I did exactly like this and it still gives me multiple volts. -6V
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You have a fault somewhere in the construction. The voltage at the speaker output should be close to zero.
Measure and record all the DC voltages like we talked about earlier. That might help show up a problem.
Measure and record all the DC voltages like we talked about earlier. That might help show up a problem.
I'm having trouble getting anything out. When I run the amplifier idle without input and load.
Current limiter kicks in and my negative voltage drops to low values...
How could I limit the current draw so that my voltage would stay constant?
Could something like resistors at +/-V rails work out?
I think the insufficient supply has been the problem here all along.
Current limiter kicks in and my negative voltage drops to low values...
How could I limit the current draw so that my voltage would stay constant?
Could something like resistors at +/-V rails work out?
I think the insufficient supply has been the problem here all along.
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If you have no load attached then the current in the neg and pos rails should at least be equal.
You need to look at why Q8 is not reducing the excess current. The voltage across R22 turns on Q8 which in turn pulls the base of Q7 down thus reducing the overall current draw. You should be way below that happening though and the circuit should be relying on the operating point of Q8 being set by R13 and R16.
Is your power supply able to supply the current needed for this amp ?
You need to look at why Q8 is not reducing the excess current. The voltage across R22 turns on Q8 which in turn pulls the base of Q7 down thus reducing the overall current draw. You should be way below that happening though and the circuit should be relying on the operating point of Q8 being set by R13 and R16.
Is your power supply able to supply the current needed for this amp ?
The supply is maxed at 3A per rail.
Ok, tomorrow, I'll probably get 5A supplies to link.
Ok, tomorrow, I'll probably get 5A supplies to link.
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You should be able to get the current right down simply by tweaking R16. If you remove R16 then TR8 should turn on and pull the current right down. If it doesn't then you have a build error or component problem.
In other words you should be able to get the amp to operate correctly at very low current settings of perhaps 100ma per output pair.
In other words you should be able to get the amp to operate correctly at very low current settings of perhaps 100ma per output pair.
I'm out of ideas.
I can't make the measurements for you. R16 doesn't affect anything.
Fuse blows out no matter what.
There must be a component problem or something like what you said but I can't pinpoint it.
TR7 was dead atleast. Checking more....
I can't make the measurements for you. R16 doesn't affect anything.
Fuse blows out no matter what.
There must be a component problem or something like what you said but I can't pinpoint it.
TR7 was dead atleast. Checking more....
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Germanium diode? My DMM tells it shorted and that it drops 0.263V Is this correct? Nvm its all good....
None of the diodes are needed for normal operation, they can be omitted and yes, 263mv is OK for Germanium.
It sounds like you have various random issues going on... more than one problem/component fault and/or construction errors.
Work through it all carefully.
It sounds like you have various random issues going on... more than one problem/component fault and/or construction errors.
Work through it all carefully.
Yes that's true. I've disassembled the breadboard. Checked all components. Every component now has been measured and made sure they are in working condition.
I'm now connecting everything one by one removing excess pin length of the components. After every placement I check the component connection to all pins.
I'm now connecting everything one by one removing excess pin length of the components. After every placement I check the component connection to all pins.
Phew.. There were still issues with connections in the board.
Now it's drawing current as it should and it's following R16. Also everything is now placed well and pin lengths shortened to keep faults off.
R22 voltage changes appropriately by R16.
Now it's drawing current as it should and it's following R16. Also everything is now placed well and pin lengths shortened to keep faults off.
R22 voltage changes appropriately by R16.
Left channel is working and biased, only little dc but its ok. I have way too little cooling but fans will help out there, atm until I get bigger cooling blocks.
It sounded great.
I think I'll assemble the right channel also and then make a table of measurements for how it performs.
It sounded great.
I think I'll assemble the right channel also and then make a table of measurements for how it performs.
Well done 
Having one channel up and running will make getting the second one operational a lot easier.
Having one channel up and running will make getting the second one operational a lot easier.- Status
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