Balder lightning guitar amp schematic please!

[J M Fahey]

Please measure the voltage pairs I suggested, there lies the path to solve the problem.
We are not guessing here but troubleshooting, which does have a standard method to follow.

[MarkusBass]

I don't remember exactly but after marking their positions and adjusting them slightly, the resistor between the drivers smoked in the center. I could see the 2 red stripes but not the multiplier so measured it at 220 ohms. I replaced that and then started blowing the output transistors. Got it to settle down but then started getting the oscillation.

Can you mark on the photo which exactly resistor have you replaced with 220 Ohms resistor? The resistor between the drivers looks like 3k6 and not 220 Ohms. Also, I wouldn't replace any resistors that were not replaced previously. You are trying to fix the amp amp not to design and manufacture a new one. The amp worked previously and you just need to fix it.
Can you verify whether the resistors that we think are 33k, are 33k, or 2k2? Just measure them.

Mark

[MarkusBass]

I suggest you leave schematic as is so we don´t lose track, but add actual PCB numbers, labels, or what´s written (or painted) on components by them, either in another colour (say, violet) or between brackets or similar, such as (R4 100k) or whatever.

It's the easiest to add component numbers in KiCad - Nick can do it. But we also need capacitor values, which should be reported by Bigdrums.

Mark

[nickb]

It's the easiest to add component numbers in KiCad - Nick can do it. But we also need capacitor values, which should be reported by Bigdrums.

Mark

As requested:



Now we need those voltages. Bring the variac to a little below the point where the current rises out of control then measure the voltages requested.

[bigdrums925]

#5 is -2.14 v
#6 is -1.65 v
#4 is - .28 v voltage here seems to change note: the resistor near #4 is 470 ohms not 47 ohms
#3 is - .15 v voltage here seems to change note: the resistor near #3 is 470 ohms not 47 ohms
#2 is .44 v
#1 is .46 v

for reference these were all taken with the variac on only 15% with a current draw of 1.4 amps

[nickb]

#5 is -2.14 v
#6 is -1.65 v
#4 is - .28 v voltage here seems to change note: the resistor near #4 is 470 ohms not 47 ohms
#3 is - .15 v voltage here seems to change note: the resistor near #3 is 470 ohms not 47 ohms
#2 is .44 v
#1 is .46 v

for reference these were all taken with the variac on only 15% with a current draw of 1.4 amps

I think #5 & #6 are transposed. So taking #6 as -2.14V I'd expect #4 to be around -3.4V yet it's -0.28V. This means the lower transistors should pass no current but we can see that the current is high at 350mA per transistor. Pull those lower transistors - one or both is likely bad.

Also, I was wrong about the 5.6k /330. Please restore to the original 33k values. The explanation is complex so I'll leave it for later.

[bigdrums925]

Yes I will post updated pics to reflect the recent changes, see below. The 3k6 resistor is now 220 ohms as original. I am only changing the resistors I changed previously.
Also I began writing in the transistor numbers and cap & resistor values in bright orange on this drawing. Please comment as needed. Never done this before.





If I understood correctly the 33k pair should be 330 and 5k6 ohms which I replaced last night
Take a look at the new pic because I'm am not sure about this.
However if you are referring to the resistors mounted perpendicular to all the rest, one of them being carbon, they are 220 ohms
My head is spinning but I am trying!

[MarkusBass]

If I understood correctly the 33k pair should be 330 and 5k6 ohms which I replaced last night

And just in the previous post Nick asked you not to do it . Are you reading the posts in this thread?
You are also using old schematic - the new one with component symbols, posted by Nick, is just 3 posts below. Please use the new one.

I asked you also to verify the value of some resistors (like e.g. 33k). Can you do it? Now, on the photo with different light, it seems to me (Nick can you verify this please) that 330R resistors are actually 220R resistors and 33k resistors are actually 2k2 resistors (the stripes are red not orange). We can only guess it based on the photo but you can verify it in less than 1 minute. Can you do it please?

for reference these were all taken with the variac on only 15% with a current draw of 1.4 amps

I never use variac with solid state amps. Instead, I use bulb limiter. The reason is simple: solid state amps are DC coupled and one voltage missing will cause all other voltages be incorrect. In your case you have two Zener diodes in the first stage of the amp. They are most probably 15V (again, could you read the symbol on the diodes?) and if you provided only 15% of the expected voltage, they will not work. It means that the input stage of the amp does not work, has incorrect voltages and all other voltages are incorrect as well. And you don't know whether this is because of a failed component, or due to missing 15V rail voltage. Variac can be only used with tube amps.

Can you also provide symbols of the transistors used in the amp (are the all BC182?) and values of capacitors. This would allow for having complete schematic of the power amp. Wouldn't you be glad having such a schematic?

Mark

[nickb]

Bigdrums - don't rely on email notifications as they often don't work. Also, if you are not using linear thread display mode, it's easy to miss new responses as they might be anywhere.

Towards the top of the page is a horizontal grey bar. At the right of it is a drop down marked 'display'. Go and select linear. Then look over the replies to see if there are any you missed.

My plan for attacking the DC problem that Mark mentioned was to leave the lower pair of output transistors off the board until we get the DC right.

Yes, it's hard to be sure of the colors from the picture so do please check them. I am updating the schematic as we go and I'll not re-post it for now to avoid confusion.

[MarkusBass]

Great work Nick. To complete the schematic you could add a Zobel network on the output (a capacitor and I think 4 parallel resistors to the ground) and a Thiele network on the output (a resistor parallel to inductor).
We are waiting for transistor types, capacitor values and 33k and 330 Ohms resistors verification.

Mark

[bigdrums925]

[QUOTE=MarkusBass;466824]And just in the previous post Nick asked you not to do it . Are you reading the posts in this thread?

Apparently I am not getting the correct sequence of the posts on my screen, didn't see his comment to put the 33k's back in until tonight, they are back in the board now

You are also using old schematic - the new one with component symbols, posted by Nick, is just 3 posts below. Please use the new one.

I will try to put transistor numbers/resistor & caps values as I am able to the newest drawing I'm able to edit.

I asked you also to verify the value of some resistors (like e.g. 33k). Can you do it? Now, on the photo with different light, it seems to me (Nick can you verify this please) that 330R resistors are actually 220R resistors and 33k resistors are actually 2k2 resistors (the stripes are red not orange). We can only guess it based on the photo but you can verify it in less than 1 minute. Can you do it please?

The 2ea 33k trim pot resistors are 33k. Even looking at the stripe colors in person it's hard to tell weather red or orange. So I am measuring them
I am having a little confusion as to which transistors/resistors/caps on the board are which on the drawing. I will verify any values I can on the latest post of the drawing I can. Also I think it may help if I assign T/R/C numbers on the drawing?
But there are none printed on the board to reference. Hopefully then the communication between us will be more clear, particularly when suggesting verification of values.


In your case you have two Zener diodes in the first stage of the amp. They are most probably 15V (again, could you read the symbol on the diodes?)

If you are referring to the ones on each side of the first trim pot they read 82x. That's all I can see without removing them

and if you provided only 15% of the expected voltage, they will not work. It means that the input stage of the amp does not work, has incorrect voltages and all other voltages are incorrect as well. And you don't know whether this is because of a failed component, or due to missing 15V rail voltage. Variac can be only used with tube amps.

I will attempt to verify the rail voltages in this circuit area and report back.

Can you also provide symbols of the transistors used in the amp (are the all BC182?) and values of capacitors. This would allow for having complete schematic of the power amp. Wouldn't you be glad having such a schematic?

I believe the BC182 is the only transistor of that type/number used in this amp. It is one of the drivers, correct? Not sure what you mean by symbols but am trying to determine which transistors on the drawing are which on the board. This should be simple but I'm not sure the drawing is correct yet. I put the transistor numbers I knew on the drawing hoping someone can tell me if I'm doing this correctly. I will continue this effort and update as I am able. I mentioned previously I have no experience making or editing drawings and only basic experience reading them. So I will be a bit slow getting the drawings/values/numbers posted and want to make sure when I do they are correct. Yes I would be very glad to have the schematic. I probably won't be able to do so tomorrow as I have a wake to go to.

[bigdrums925]

Just saw the trace drawing. Shall I attempt to verify? i.e. I only see two traces going to the temp sensor/bias transistor?
It will take me some time to do this though as I have to do them one by one. Please bear with me as I very much appreciate the help!

[MarkusBass]

I believe the BC182 is the only transistor of that type/number used in this amp.

That's not true. Half of the transistors are of PNP type and they must be of different type (BC182 in NPN).

EDIT: complementary transistors to BC182 are BC212. Please check whether some of the transistors on the board are BC212.

If you are not sure where the transistors are on the schematic, you can simply put its symbol on the photo you posted previously. You can do it even with Paint. The same applies to capacitors. Just put the values on the photo and Nick will put them on the schematic.
I read the forum in linear mode. In this case, the latest post is always on the top and it is not possible to miss posts. You can select it in the top-right corner of the screen. Like this:




Mark

[bigdrums925]

I marked up the picture with the transistor #/resistor values/cap values or number/diode value or number



Hopefully now when I'm asked to check this part or value we can do it with callouts from the schematic and I will know exactly where.

[MarkusBass]

OK. Now it looks much better but there is still some work to be done. It's because I see that several components were replaced in a random way and I'm not sure whether the values are correct.
What I see is:
- power transistors are from different production series (in pairs), which is not allowed. Did you replaced just two of them instead of four?
- low power transistors are of different types (previously you said that all of them are BC182). Did you replace any of the low power transistors, or it was like this from the very beginning? I hope that you are aware that BC182 has different pinout than MPSA06. You have to be very careful when replacing one with the other.
- some capacitors are still not labeled (for example on the top of the board there are three capacitors but only two of them are labeled). Can you fix it?
- can you check what is the Zener diode on the top of the board?
At least two resistors are labeled incorrectly: the resistors on the left of the board are either 68 Ohms, or maybe 6R8. Can you measure them directly in the board?
- the resistor in the second column from the left (third from the top) is marked as 33k but I can see that this is either 330R, or 220R. Can you measure it in the board? BTW, it looks like it was replaced. Did you do it?
- the resistors that we thought that we are 33k, are actually 2k2 (as I thought). The 330R resistors are actually 220R.
- Zener diodes on the input are 15V (I thought so).
- it looks like some of the resistors were replaced (by you or someone else). For example, the famous resistor 220R, which you replaced with 3k6 resistor. What else did you replace?
- are there any additional resistors below BD419/420 heatsinks?
- the bias trimmer is very sensitive in this amp. You marked its initial position and started turning it. You shouldn't do it if you don't know how to verify the bias settings.
- what are the power supply rails? +/-40V, or 45V?

BTW, 33k resistors in series with the trimmer (or even 2.2k) in the bias circuit will not work correctly. Did you replace any of them?

I know how the amp works (even without the information you haven't provided). I could fix it but it's to far. Please provide the information listed above because we need to have a correct schematic first.

Mark