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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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3rd Oct 2010, 1:32 pm | #41 |
Hexode
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Re: Leak Delta 30 Amplifier - One Channel Down
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3rd Oct 2010, 1:32 pm | #42 |
Nonode
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Re: Leak Delta 30 Amplifier - One Channel Down
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3rd Oct 2010, 1:37 pm | #43 |
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Re: Leak Delta 30 Amplifier - One Channel Down
Alistair.
There's no difference in what we say about leadouts. We're just looking at different orientations of the transistors. However you've posted a link with a nice picture which is better. Wage Slave. Check that the transistors are fitted correctly.
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3rd Oct 2010, 1:37 pm | #44 | |
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Re: Leak Delta 30 Amplifier - One Channel Down
Quote:
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3rd Oct 2010, 1:37 pm | #45 | |
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Re: Leak Delta 30 Amplifier - One Channel Down
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3rd Oct 2010, 1:42 pm | #46 |
Hexode
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Re: Leak Delta 30 Amplifier - One Channel Down
They are correct.
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3rd Oct 2010, 1:42 pm | #47 | ||
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Re: Leak Delta 30 Amplifier - One Channel Down
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3rd Oct 2010, 2:01 pm | #48 |
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Re: Leak Delta 30 Amplifier - One Channel Down
T4 is pulling current from somewhere. It's coming out of the collector and passing through R32 giving a volt drop of 1.6V across it indicating a current of 1mA. That current must be coming from somewhere. If it were entering the base it would have to pass through R29 giving a large volt drop across it. However the base voltage is normal. The current can't be coming through R31 as 1mA flowing through it would give a volt drop of about 15V. I conclude that the current is coming through T5. Remove T5 and see if that makes any difference to the readings on T4. While T5 is out test it.
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3rd Oct 2010, 2:08 pm | #49 |
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Re: Leak Delta 30 Amplifier - One Channel Down
So I redid all the transistor measurements. Almost identical:
T5 Collector 34.2V (spec=35V) Base 30.7V (spec=14V) emitter 30.2V (spec=13.5V) T4 Collector 31.3V (spec=14V) Base 1.9V (spec=2V) emitter 1.6V (spec=1.5V) T3 collector 32.9V (spec=31V) Base 29.5V (spec=19.5V) emitter 28.8V (spec=19V) T2 collector 31.8V (spec=19.5V) Base 0.6V (spec=4.0V) emitter 0.1V (spec=3.5V) T1 collector 0.2V (spec= 4V) Base 0.1V (spec= ?) emitter 0.0V (spec=?) |
3rd Oct 2010, 2:09 pm | #50 |
Hexode
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Re: Leak Delta 30 Amplifier - One Channel Down
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3rd Oct 2010, 2:19 pm | #51 |
Hexode
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Re: Leak Delta 30 Amplifier - One Channel Down
No, I was wrong. I didn't do any measurements, just tested T5 with the diode testing range of the multimeter. It seemed fine. Do you want me to go ahead and pull it again to measure the effect on T4?
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3rd Oct 2010, 2:21 pm | #52 |
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Re: Leak Delta 30 Amplifier - One Channel Down
Check the voltages across R34 and R35. With near 30V on the emitter of T5 they should both have about 15V across them.
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3rd Oct 2010, 2:22 pm | #53 |
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Re: Leak Delta 30 Amplifier - One Channel Down
Hang on. I'm taking it out.
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3rd Oct 2010, 2:32 pm | #54 |
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Re: Leak Delta 30 Amplifier - One Channel Down
OK T4 with T5 removed is:
Collector 41V Base 2.3V Emitter 2.0V Testing it again..... |
3rd Oct 2010, 2:39 pm | #55 |
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Re: Leak Delta 30 Amplifier - One Channel Down
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3rd Oct 2010, 2:44 pm | #56 |
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Re: Leak Delta 30 Amplifier - One Channel Down
The emitter of T4 is reading 2V, so there's now 2mA flowing through it. This current can't be coming through R31 or there'd be a volt drop of about 30V across it, which there clearly isn't. The only other way into T4 is through the base and the current doesn't seem to be entering T4 there either. I need a long think about this. In the mean time it would be useful to measure the voltage across the resistors around T4/T5 with T5 out.
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3rd Oct 2010, 2:53 pm | #57 |
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Re: Leak Delta 30 Amplifier - One Channel Down
Hi Guys Looking at all those measurements and the different transistors I am now wondering if the schematic is not the correct one for this board. I am also now wondering is the board has DC coupled stages. Originally it seemed that there were 2 faults (T1/2 & T4/5). It could be that there is only 1. I am suspicious of R15 (470K), T1 being a little leaky or T2 drawing too much base current.
Al
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3rd Oct 2010, 2:56 pm | #58 | |
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Re: Leak Delta 30 Amplifier - One Channel Down
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Enjoy the rest of Sunday guys. Edit: T5 seems to test OK. Last edited by Wage Slave; 3rd Oct 2010 at 3:03 pm. |
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3rd Oct 2010, 3:04 pm | #59 | |
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Re: Leak Delta 30 Amplifier - One Channel Down
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3rd Oct 2010, 3:11 pm | #60 |
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Re: Leak Delta 30 Amplifier - One Channel Down
Even comparative resistance measurements might help narrow down where the problem lies.
My earlier comment about T1 and R15 would only apply if that part of the board matched the cct. Al
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