A non-PL quasi-comp output transistor question

Gepetto

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62vauxhall said:
Am using a DBT

No, the readings I got were:
Q607 Emitter - (-)34.0 volts
Q609 Emitter - (-)34.6 volts
Click to expand...
Well now. you indicated that the collector of Q603 is showing +48V and now you are reporting that Q607 emitter is -34V. There in lies a problem since the base of Q607 is directly connected to the collector of Q603.

Blown base emitter on Q607????

You cannot have both readings without something wrong there. It seems like your front end is intact and working (Q601, 602, 605, 606)
 
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Yes, sorry, there is something wrong....my eyesight, concentration, memory, whatever.

That +48 volts was at the base of Q603 not the collector. Collector voltage (-)33.6 and that jives with Q607's base voltage.

For what it's worth, over the past couple of weeks, I have pulled all of the transistors from this board, some more than once, and checked them with one of those $20 multi-testers. That device displayed BJT for each so that made me think they were all OK.
 
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Next measure the voltage ACROSS R606 and R610 and report back.

R610 should have a much higher voltage if the front end is working.

Also report the voltage ACROSS R611 and report back.
 
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R611 should have the same voltage across it as R607. Measure R607 and see if you are getting ~1V. You are operating off of a DBT so it is doubtful that you have the full rail voltage. Have you measured the rail voltage?

Q603 forms a current source with a nominal current of 7.5mA

The readings on R606 and R610 show that the front end is trying to do the right thing.
 
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Across R607 is 107mv with DBT. Not near 1v and not quite the same as R611 (91mv).

Since you mentioned it, I checked rail voltages. With DBT is 50v - no DBT is 59v.
 
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Something not adding up. Earlier you said you had 48V on the base of Q603 which implies 2V between the 50V rail and the base of Q603.

You indicate R607 has 107mV. What does D601 and R608 have across each?

Is R613 any good? Open, partially open?

You have to get this current source working properly or else you have nothing.

The R607 - D601 - R608 chain forms a simple voltage divider. With your 50V rail reading with the DBT and with your DVM negative probe on ground, the top of R608 should read 48.2V, then 48.9V at the anode of D601 and then 50V at the top of R607.

Do you copy on these approximate readings?
 
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62vauxhall

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Across D602 is 56.4 volts
Across R608 is 48.4 volts

R613 measures at 358 ohms - within spec of 330

Measurments as per instructions:
R608 - 47.9 volts
D601 anode - 47.8 volts
R6107 - 48.4 volts

Yes,the latter three readings approximate those you cited.
 
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62vauxhall said:
Across D602 is 56.4 volts
Across R608 is 48.4 volts

R613 measures at 358 ohms - within spec of 330

Measurments as per instructions:
R608 - 47.9 volts
D601 anode - 47.8 volts
R6107 - 48.4 volts

Yes,the latter three readings approximate those you cited.
Click to expand...
Hmmm still not seeing the consistency in this. In the top half of the response you say that there is 48.4V across R608
Across R608 is 48.4 volts
and then in the second measurement
R608 - 47.9 volts

These are the same reading yet reporting a half a volt difference.

What voltage are you measuring ACROSS R618? It is a 10 ohm resistor that feeds the collectors of Q607 and Q609.

Are R632 and R633 measuring about 10 ohms?

Is the transistor in the Q001 position that you thought was good really good? Same for the Q003 transistor in the bottom half
 
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The duration of time the amplifier is on seems to account for the voltage differences across R608. It's not stable. I re-checked immediatly after switching the power on and the meter read 49 volts. Ten or so minutes later 47.8 volts. Five minutes more 48.5 volts. A further five minutes 47.6 volts.

R632 measures 9.6 ohms
R633 measures 9.2 ohms

Regarding the TO3 output transistors, I can only say that the device I used failed to identify two of the eight as BJT transistors. The other six were identifed correctly - BJT transistors which meant good or so I thought. The only other method I can use is a DMM. More time consuming which was why I purchased that multi tester.

The way you phrased the last line was my subject question. If Q001 is on top and Q003 the bottom, then I have installed them wrong. I have the two transistors on the bottom.

I thought this was the orientation so installed transistors at Q002 and Q004. I have them side by side not above and below.

Q001****Q003

Q002****Q004

But this is layout instead? If so, then I currently have one transistor at Q003 and the other at Q004.

Q001****Q002

Q003****Q004
 
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62vauxhall said:
The duration of time the amplifier is on seems to account for the voltage differences across R608. It's not stable. I re-checked immediatly after switching the power on and the meter read 49 volts. Ten or so minutes later 47.8 volts. Five minutes more 48.5 volts. A further five minutes 47.6 volts.

R632 measures 9.6 ohms
R633 measures 9.2 ohms

Regarding the TO3 output transistors, I can only say that the device I used failed to identify two of the eight as BJT transistors. The other six were identifed correctly - BJT transistors which meant good or so I thought. The only other method I can use is a DMM. More time consuming which was why I purchased that multi tester.

The way you phrased the last line was my subject question. If Q001 is on top and Q003 the bottom, then I have installed them wrong. I have the two transistors on the bottom.

I thought this was the orientation so installed transistors at Q002 and Q004. I have them side by side not above and below.

Q001****Q003

Q002****Q004

But this is layout instead? If so, then I currently have one transistor at Q003 and the other at Q004.

Q001****Q002

Q003****Q004
Click to expand...
I have no idea whatsoever the orientation they have set out in the amp as I have no point of reference at all. You will have to trace it out. You need one good transistor in either Q001 or Q002 (it does not matter which) and one good transistor in either Q003 OR Q004 (again, it does not matter which)

Do you have a diode scale on your meter? If so, forget the transistor checker and use the diode function.

On each test, record the meter reading.

With positive lead on the base and negative on emitter = ?
With positive lead on the base and negative on collector = ?
With positive lead on the emitter and negative on collector = ?
With positive lead on the collector and negative on emitter = ?
With negative lead on the base and positive on emitter = ?
With negative lead on the base and positive on collector = ?

These readings will give you a good idea whether you have good transistors or not.
 
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I did have the outputs in correct positions. I "followed the wires" when I installed them a few days ago.

Here are the readings obtained via DMM for the two 2SD426's which I had in Q002 & Q004. From what I understand, acceptible for NPN.

With positive lead on the base and negative on emitter = .498.......500
With positive lead on the base and negative on collector = .466.......479
With positive lead on the emitter and negative on collector = OL.........OL
With positive lead on the collector and negative on emitter = OL.........OL
With negative lead on the base and positive on emitter = OL.........OL
With negative lead on the base and positive on collector = OL.........OL
 
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62vauxhall said:
I did have the outputs in correct positions. I "followed the wires" when I installed them a few days ago.

Here are the readings obtained via DMM for the two 2SD426's which I had in Q002 & Q004. From what I understand, acceptible for NPN.

With positive lead on the base and negative on emitter = .498.......500
With positive lead on the base and negative on collector = .466.......479
With positive lead on the emitter and negative on collector = OL.........OL
With positive lead on the collector and negative on emitter = OL.........OL
With negative lead on the base and positive on emitter = OL.........OL
With negative lead on the base and positive on collector = OL.........OL
Click to expand...
Yes those look good and good that they are in the correct locations.
 
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I don't see that you answered this earlier question, sorry if I missed it.

What voltage are you measuring ACROSS R618? It is a 10 ohm resistor that feeds the collectors of Q607 and Q609.
 
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My bad. I did measure across R618 but neglected to include the number. It was 74mv.
And confirmed just now - 74mv.

EDIT: still using the DBT
 
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62vauxhall said:
Voltage across R619 - 294mv
Voltage across R617 - 60mv
Click to expand...
That shows that the first and second stages are working properly.

I am suspicious of your current source formed by Q603. Suggest tacking a 10K resistor from the positive rail (top of R611) to the collector of Q603 to see if it moves the needle or not.
 
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