Now you know either Q1 or 4 are conducting too much or Q2 or 6 aren't conducting enough. I'm thinking the issue is in the positive side.
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To me the next logical step would be to lift a leg on R14 and 17, then measure base voltages on Q4 and 6 to see if that imbalance goes away. If that balances out jump a resistor from Q4 emitter to Q6 emitter to simulate a load and see if everything is still balanced. I'm thinking around 1K should be well under 25ma load. Feel free to chime in anyone if this is bad advice.
Hi
If one half works and the other not I think is time to check all the semis.
I hope you compared the two PC board (resistors code marks, caps etc.)😎
That just an opinion.😀
Greetings
Check the value of all the passive components first. Then swap the active ones one by one with the good board, starting with the transistors.
What keeps bothering me is 22V on the bases of Q7 and Q2. That made me suspect R20. So I measured it and it "winds up" to 470R from about 380R like it has a cap across it but it doesn't. I checked the good board and it just measures right at 470R so I pulled R20 and out of circuit it measures normally. Just to test, I powered up without R20 in circuit and I still have 26V on the bases of Q7 and Q2. It just gets weirder.
I'm at a loss for the voltage being present with the resistor unhooked. Is the output end still running warm with ND and NP disconnected?
I pulled R20 in the spice file and still have 16V on the base of Q7. I think ti feeds through the vbe of Q8 and Q7. I just replaced Q7 and Q8 just for cause. No change. I may just give it up on this board. I lost traces on the last swap. That's the problem with these cheap boards. They can't take too much abuse. I got the one board working so It has been proofed. I just wanted the second board working so I could give it a good listen.
Blessings, Terry
Blessings, Terry
Q2 would either have to conduct through the cap or through Q6 ... but
Terry said that (Q6) was
That makes no sense either, since Q6 would have to conduct if Q5 does -
(mirror) ? Q5's current is set by (it's) Vbe + R9's voltage drop.
OS
Terry said that (Q6) was
.... "dead".
That makes no sense either, since Q6 would have to conduct if Q5 does -
(mirror) ? Q5's current is set by (it's) Vbe + R9's voltage drop.
OS
Almost worth slugging it out and finding what's wrong. This is weird. I'm still a firm believer in breaking it down into smaller sections and zeroing in that way. That's why I suggested lifting legs on R14 & 17.
As you know, I'm just trying to learn. When I look at the voltages I have, I see -10.56 on Q5 emitter and -9.97 on the base, that is .590 vbe So now that I look closer I see that I have basically the same on Q6 so I guess it should be conducting but I have +6.09V on the collector so I'm confused. Q2 has 6v vbe yet the transistor has been replaced twice without change. It also runs very hot! Q10 runs very hot as well. That has been replaced too.
I've had enough for today. Thanks to everyone for all the suggestions. I'll give some more thought in the morning.
Blessings, Terry
I can't decide ???
Below 1/2 .....
1- is the "GLA" 2 stage LTP Japanese amp goodness 😀 .
2- is the "vzaichenko" version - like his tube amp , same as the
GLA but with a symmetric 2'nd stage.
Both have 12 devices , both can now "eat" the square waves
and clip all day.
Still can't decide - only 1 will be picked.
Oh , the ASC's are below ...too.
PS - most of us listened to these amps in College (70-80's).
OS
Below 1/2 .....
1- is the "GLA" 2 stage LTP Japanese amp goodness 😀 .
2- is the "vzaichenko" version - like his tube amp , same as the
GLA but with a symmetric 2'nd stage.
Both have 12 devices , both can now "eat" the square waves
and clip all day.
Still can't decide - only 1 will be picked.
Oh , the ASC's are below ...too.
PS - most of us listened to these amps in College (70-80's).
OS
Attachments
Me ,too. Q10 ? - did you not have a pair of those to-126's in backwards ?
Maybe one got damaged ?
Ah , sleep time - I'm mental ...(ly) challenged now 😀 - night.
OS
They measured OK but I replaced them today just to be sure. This is a tough one. I may get ambitious tomorrow and etch a new board for this side and just start over with it. Probably swap over the caps and just install all new devices. I'll see how I feel in the morning.
Blessings, Terry
Blessings, Terry
C11 seems to have been shot. It's biased backwards, and has about 20+ mA DC through it. Replace with a non-polar and carry on troubleshooting.
C11 could be a good cap before powering up, then got destroyed by the backwards bias stemmed from something else that was not right.
Hi Esperado,I have a working amplifier(post#4812)http://www.diyaudio.com/forums/solid-state/248105-slewmaster-cfa-vs-vfa-rumble-482.html, What is the recommend specific values for feedback resistance(values that you prefer)??
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From the voltages in your schematic in #4826.
R17 has 20+ mA going through, about 1 mA bled through Q6, the rest has to go to GND through C11.