Balder lightning guitar amp schematic please!

[MarkusBass]

The latest schematic is here: http://music-electronics-forum.com/t45081/#post466975 . i thought that you fired up the amp without the output transistors (and then got smoke). You didn't tell us this .
What is the voltage on any of R36-46 resistors? Can you change it with bias trimmer?

Mark

[nickb]

Is there a updated schematic available?

The edit post period has expired so I'll have to post fresh. Here is the latest sch V0.5


PS: Thanks again to Doug and his eagle eyes else we would have not got here for a long time.

[MarkusBass]

I think that this is version 1.0. The only thing that seems to me that is incorrect, is that 4x68 Ohms resistors are in series with capacitor in the Zobel network and the output coil is in parallel to a single resistor (1R6) - at least it seems to me.
Great job.

Mark

[J M Fahey]

Removed and tested Q8, Q9, Q1, Q3, Q5, Q2, Q4, Q7. All checked good. I checked Q6 recently.
With the 4 output transistors in I powered up slowly with the variac and the current draw rises sharply at about 15%
I removed Q9 but still have the excessive current draw so until I remove at least some of the outputs I won't be able to measure around Q5, Q6, Q7.
Any suggestions beyond removing the outputs?
Still not showing bad outputs though....

Trying to get back in the action but again dismayed when seeing that instead of **essential** voltage measurements we get endless useless shotgunning and parts removal and reinsertion with no clue or purpose.
Doubly so in an amp which is already suffering from track destruction, even worse because it uses outdated taped PCB design, guaranteed to produce thin flimsy tracks, which must not be messed with if at all possible.

Not surprisingly parts check good but amp does not work.

Hint: I couldn´t care less about how a transistor measures outside the amp, all that matters is Vce and Vbe *in circuit*.
Outside measurement is only a confirmation of what I *already* found in the circuit, not the other way around.

[nickb]

Bigdrums - there seems to be a real problem here. Either your are missing posts in the forum or are simply ignoring instructions. Don't rely on email updates at you wont get all the posts. Did you switch to linear mode?

We did get voltage readings which told us one or both of the PNP output transistors were bad. After that it went off the rails as the next step response was either not followed or missed. Example, you had been told to remove both the lower transistors and the do some more testing. This was get things to a good state to avoid blowing up more transistors but you went ahead and replaced them.

Never mind. They are in now so go and redo the voltage measurements. Did you look at the pdf of expected voltages? Use it as a guide on what you should see.

[bigdrums925]

My apologies for any misunderstandings. I don't think I am missing any posts since switching to linear mode. And I don't rely on email updates. I have this thread in my favorites and it takes me here every time. Also I am not ignoring instructions, rather occasionally am confused by what exactly I should do and in what order. In one post for example I was told it doesn't matter what measurements say with parts changed or removed, and to get it back the way it was with all the parts re-installed. Then when I read I should remove the lower transistors. What does "lower" mean? That particular instruction was a difficult one to interpret.
We recently have a mostly complete schematic and I would hope for clarity we could used the callouts i.e. Q10, Q13. Are those the 2 transistors lower means?
Again, I apologize for any misunderstanding, and I am aware some if not all of you guys are becoming frustrated with me. That is the last thing I want to happen.

If I remove the 2 lower transistors (Q10, Q13 I believe) I should be able to power up fully. Q10 was shorted and has been removed. I will remove Q13 as well and take the measurements. I was asked to take them at R36-R46 I think. For the record I started doing that last night and got 0 volts. Found the 2 PS fuses were blown. I replaced them this morning only to find the 1 shorted output Q10 which I removed. BTW in post #75 above I said that Q13 was shorted. I believe it was in fact Q10.

I was also asked to test Q8 and Q9. If ok test Q5, Q5, & Q7. If that is inconclusive, remove Q9, power up and measure voltages around Q5, Q6, Q7.

volts to ground with Q10 & Q13 removed:
Q5: e 45.6, b 45, c 0.5
Q6: c 0.5, b -1.1, e -1.8
Q7: c -1.8, b -44.8. ,e -45.3

r36: .53
r37: .53
r38: .53
r39: .53
r40: .53
r41: .53
r42: .53
r43: .53
r44: .53
r45: .53
r46: .53

I hope this is complete and what you were asking for. I will wait for further instructions before changing anything, and thank you all

[bigdrums925]

The latest schematic is here: http://music-electronics-forum.com/t45081/#post466975 . i thought that you fired up the amp without the output transistors (and then got smoke). You didn't tell us this .
What is the voltage on any of R36-46 resistors? Can you change it with bias trimmer?

Mark

Checked voltages on R41 to ground. Still 0.53v and the trim pot does not change that number.

[nickb]

Success! Those voltages are good. Q10 and Q13 are not fitted and that part of why you cannot bias it. The other reason is R11 is too high but we'll get to that.

Do not connect a load until we say to do so.

The next step is to fit Q10. Please note Mark's point about transistors being from the same batch. If you don't follow his advice there is a very good chance of blowing them up again on high output volume. With Q10 fitted you should be able to bring up to full voltage, but do so carefully. Measure across R38 and check you get no more than 30mV. If excessive back off the variac and check the voltages around Q6 again. More likely you won't be able to get to 30mV and will need to change R11 to 8.2k. Also check the output voltage is <1V. Now adjust RV1 to get close to zero on the output. Next adj RV2 to to get 25mV across any of the 1.3 ohms resistors.

[bigdrums925]

Success! Those voltages are good. Q10 and Q13 are not fitted and that part of why you cannot bias it. The other reason is R11 is too high but we'll get to that.

Do not connect a load until we say to do so.

The next step is to fit Q10. Please note Mark's point about transistors being from the same batch. If you don't follow his advice there is a very good chance of blowing them up again on high output volume. With Q10 fitted you should be able to bring up to full voltage, but do so carefully. Measure across R38 and check you get no more than 30mV. If excessive back off the variac and check the voltages around Q6 again. More likely you won't be able to get to 30mV and will need to change R11 to 8.2k. Also check the output voltage is <1V. Now adjust RV1 to get close to zero on the output. Next adj RV2 to to get 25mV across any of the 1.3 ohms resistors.

Installed Q10 and ramped up variac. I know you know your stuff but is it really R11 that needs to change to 8.2k?
I ask because R26 has a side note of recommend 8.2k instead of 33k.
Problem: while checking for 30mV the second time both PS fuses blew and it shorted Q10 between emitter and collector. No significant current draw noted.
I very carefully ramped up the variac each time watching the amp meter, very little meter needle movement less than 0.2 amps.
VOM Meter read 0.2mV max
Looks like Q10 socket has a problem, each time one blows its in that position.
Compared Q10 & Q13 terminals (without transistors) with meter and they are the same
When should I put Q13 back in?

Awaiting your instructions....

[nickb]

Sorry it wa a typo, did mean R26 but we're not ready for that yet.

Leave Q10 and Q13 out, bring up variac and measure around Q8 qnd Q9. I suspect Q9 is bad. Also check R33 is not open as you did once mention it smoked.

[bigdrums925]

Q8 & Q9 both check ok and the voltages seem good, 46v other side -46v, 1.1v, -1.1v, 0.5v, -0.5v etc.
Every place I checked it's opposite was pretty much right there in negative.
R33 still checks 220 ohms.

[nickb]

Measure again but this time on the actual pads of Q10-Q13.

Also look again at R26. From your measurements you have 0.7v across the base and emitter of Q6 and 1.6 from base to collector. If both resistors are 33K and the trimmer is midway then you should 0.7v across both, ignoring any small base current. To get what you see, I'd expect R26 would to be around 10K. So something is wrong there.

[bigdrums925]

Q10 & Q13 collector - 46.1, emitter 0.5, base - 0.5

for what its worth voltage drop across R25 is 1.68 and R26 is 0.65

Yes 0.68 across base and emitter and 1.76 across base and collector on R26

both 33k resistors measure the same and I adjusted slightly trim pot to (equal resistance) center before taking above measurements

[MarkusBass]

Nick,

I also have simulation of this power amp. But I got different result regarding the 33k resistor changed to 8.2k. I wonder what is the reason of the discrepancy. One of the possibilities is that I use different transistors than you do. I use MPSA06 , MPSA56 and MJL21193/194. I simulated the quiescent current through one of the ballast resistors (so the current through output transistor will be twice higher) and here is what I got:

This is the resistor set as a parameter to the following list: 8.2k, 22k , 33k. With 8.2k I get the current from 140mA to 240mA. This is definitely to much. With 22k the current is from 2mA to 18mA. This one looks very good. And with 33k the current is exactly 0mA. It means that the amp works in class B and who knows - maybe it was designed in this way. Don't you think? I check also that in this case the output signal is correct.
To see it better I remover the 8.2k from the list (so now the graph is only for 22k and 33k) to see more details. This is what I got:

Looks very good. If Bigdrums claims that he didn't change the 33k, maybe this was in the original design of the amp? I would change only one resistor in the amp: 220 Ohms in the feedback loop (to e.g. 820 Ohms).

@Bigdrums: for me it is very difficult to advise you what you should do because you are not following what you are asked for. You showed desoldered power transistors so I thought that they are desoldered all the time. But then, after few failures of the amp, you say that one of the output transistors was shorted. So you soldered and desoldered the transistors several times and couldn't check that some of the transistors are shorted? . For me it's clear that you still have some transistors shorted and if I were you, I would try to power up the amp without the output transistors and verify whether it works (of course without any load).
You've got a great present - amp schematic, which is not available anywhere else in the world, you got simulations proving that the amp works correctly (if not the shorted transistors). Please use it wisely.

Mark

[bigdrums925]

I think R44,R45,R46, & R47 are tied to the power transistors output ahead of the 1.6 ohm resistor R48 and inductor L1 instead of after.
and that there is another (disk) cap labeled "683M" before the 0.22uF cap C9 going to "ground"
This "ground" is going directly to the collectors of Q11 & Q12.
Does this make any sense? That is to the voltage supply 46.6v