Disregard the pink arrows. I just couldn't find a pic without them. Sorry.

Where does the wire marked with the green arrow go? I can't see it clearly in this picture.

Quote from: Miyagi_83 on December 09, 2024, 05:32:35 PMJay, regarding your preamp settings for the distortion demo

Quote from: RG100ESROXPreamp settings were: P10-B0-M0-T10 (and pulled for clipping)-V3~4-G10

How did you have reverb set? The RCA connectors for the reverb have not been plugged in, and the reverb setting is always at zero.
I'm just thinking out loud now, BUT... Good. I like the idea.

If there is something wrong with the power amplifier's power supply (negative rail measures positive now, according to the image you attached earlier), there might have been a fault in the reverb driver's supply which caused a voltage drop across the op amp, which in turn led to clipping in the op amp itself, which was then blended with the signal. Does that make sense? Yes. However, it occurred to me at some point a while back that maybe the OpAmp was to blame. So, I removed it as well as replacing it with a known good IC4558, and it did not change anything.
Could you measure the voltage at pins 4 & 8 of the 1458? Sure. Last time I did. The voltages were as spec'd on the data sheet for it. I'll check em again just be sure they're still to spec.
And be sure to examine the power supply: rectifier, filter caps, Zener diodes and so on.
M. What am I looking for specifically? Voltages? What is the best way to test the diodes in a circuit? Or does it matter that they are in circuit, and will test fine regardless?

Also, I did replace the rectifier (see attached photo) with one of a higher amperage rating at one point a while back. I don't think this would have anything to do with what's going on, or am I wrong? It should be no different than the one that was in there, except it'll handle more current.

IC4558:
PIN 4 = -12.45VDC
PIN 8 = +12.45VDC

Quote from: Miyagi_83 on December 09, 2024, 05:59:12 PMDisregard the pink arrows. I just couldn't find a pic without them. Sorry.

Where does the wire marked with the green arrow go? I can't see it clearly in this picture.

That black wire connects the + side of the left filter can, and - side of the right filter can to ground. (see attached photos)
 

Quote from: RG100ESROX on December 09, 2024, 06:52:06 PMThe RCA connectors for the reverb have not been plugged in, and the reverb setting is always at zero.
...
 Yes. However, it occurred to me at some point a while back that maybe the OpAmp was to blame. So, I removed it as well as replacing it with a known good IC4558, and it did not change anything.
...
IC4558:
PIN 4 = -12.45VDC
PIN 8 = +12.45VDC

My idea was that if the voltage across the op amp was too low, it would clip at less input signal, even if the device itself was in perfect condition. For example, if you power an operational amplifier with 9VDC, it will not put out a signal larger than 7-8 Vpp (less?) because signal can't go further than power supply rails, and in op amps it's a little less than that. So, the input signal will be amplified until it hits the power supply rails where it will be clipped off.
Nonetheless, we can assume that the reverb driver is powered properly, and the extra distortion was generated elsewhere, especially that the reverb pot was turned down to zero, so nothing should have been able to sneak into your signal. I'll keep thinking about it, though.

QuoteWhat am I looking for specifically? Voltages? What is the best way to test the diodes in a circuit? Or does it matter that they are in circuit, and will test fine regardless?

First of all, orientation, especially on components that you replaced, especially polarity-sensitive ones. In circuit, most probably you won't be able to test them correctly because they interact with each other.
First, however, I would do voltage tests around the power supply, points marked A, B, C, and D on the schematic (although C and D seem fine, judging from your op amp test).
For some reason your negative rail (point B) is positive and I'm trying to wrap my head around it. What about the positive rail (point A)?

Maybe test ground connections too?

QuoteAlso, I did replace the rectifier (see attached photo) with one of a higher amperage rating at one point a while back. I don't think this would have anything to do with what's going on, or am I wrong? It should be no different than the one that was in there, except it'll handle more current.

Yeah, a beefier rectifier will do no harm. It's like installing a drain pipe of a larger diameter, it's going to do the same job, but it will be able to take more water. Unless it's dud of course, but yours probably is fine.

Quote from: RG100ESROX on December 09, 2024, 07:41:03 PMThat black wire connects the + side of the left filter can, and - side of the right filter can to ground. (see attached photos)

Thank you. So, that's a ground lug there, underneath the black wire going to the pilot lamp? Make sure it makes good contact with the chassis.

Where is the transformer center tap connected?

M.

Quote from: Miyagi_83 on December 10, 2024, 12:31:11 AM

Quote from: RG100ESROX on December 09, 2024, 06:52:06 PMThe RCA connectors for the reverb have not been plugged in, and the reverb setting is always at zero.
...
 Yes. However, it occurred to me at some point a while back that maybe the OpAmp was to blame. So, I removed it as well as replacing it with a known good IC4558, and it did not change anything.
...
IC4558:
PIN 4 = -12.45VDC
PIN 8 = +12.45VDC

My idea was that if the voltage across the op amp was too low, it would clip at less input signal, even if the device itself was in perfect condition. For example, if you power an operational amplifier with 9VDC, it will not put out a signal larger than 7-8 Vpp (less?) because signal can't go further than power supply rails, and in op amps it's a little less than that. So, the input signal will be amplified until it hits the power supply rails where it will be clipped off.
Nonetheless, we can assume that the reverb driver is powered properly, and the extra distortion was generated elsewhere, especially that the reverb pot was turned down to zero, so nothing should have been able to sneak into your signal. I'll keep thinking about it, though.

QuoteWhat am I looking for specifically? Voltages? What is the best way to test the diodes in a circuit? Or does it matter that they are in circuit, and will test fine regardless?

First of all, orientation, especially on components that you replaced, especially polarity-sensitive ones. In circuit, most probably you won't be able to test them correctly because they interact with each other.
First, however, I would do voltage tests around the power supply, points marked A, B, C, and D on the schematic (although C and D seem fine, judging from your op amp test).
For some reason your negative rail (point B) is positive and I'm trying to wrap my head around it. What about the positive rail (point A)?

Maybe test ground connections too?

QuoteAlso, I did replace the rectifier (see attached photo) with one of a higher amperage rating at one point a while back. I don't think this would have anything to do with what's going on, or am I wrong? It should be no different than the one that was in there, except it'll handle more current.

Yeah, a beefier rectifier will do no harm. It's like installing a drain pipe of a larger diameter, it's going to do the same job, but it will be able to take more water. Unless it's dud of course, but yours probably is fine.

Quote from: RG100ESROX on December 09, 2024, 07:41:03 PMThat black wire connects the + side of the left filter can, and - side of the right filter can to ground. (see attached photos)

Thank you. So, that's a ground lug there, underneath the black wire going to the pilot lamp? Yes; it is. Make sure it makes good contact with the chassis.

Where is the transformer center tap connected?

I'll check. Thanks for all of your help and input. It's most appreciated.

I'll try and find the post where g1 requested the voltages of the 'A' through 'E' points on the schematic. I will double check them again to see if they remain the same as previously posted.

M.

Quote from: RG100ESROX on November 25, 2024, 06:51:19 PM

Quote from: g1 on November 25, 2024, 03:37:05 PMThat's fine if you had the gen. set for low level output.
Check the amps power supply (DC)voltages, shown as  A,B,C,D,E on the schematic.

VOLTAGES REQUESTED:

A =   41.90VDC
B = -41.60VDC
C =  12.61VDC
D = -12.60VDC
E =   25.38VDC

I found them. 2 weeks ago they were fine, so you might have made a mistake in your labelling, but do check again, just to be sure.

Edit: BTW, do you have another voltmeter on hand that you could try? The incorrect readings might be caused by a number of factors. Faulty or poor-quality test equipment, faulty component(s) in the circuit, or human error come to mind.

Quote from: Miyagi_83 on December 10, 2024, 04:32:41 AM

Quote from: RG100ESROX on November 25, 2024, 06:51:19 PM

Quote from: g1 on November 25, 2024, 03:37:05 PMThat's fine if you had the gen. set for low level output.
Check the amps power supply (DC)voltages, shown as  A,B,C,D,E on the schematic.

VOLTAGES REQUESTED: I will get these voltage readings for you later this morning.

A =  41.90VDC
B = -41.60VDC
C =  12.61VDC
D = -12.60VDC
E =  25.38VDC

I found them. 2 weeks ago they were fine, so you might have made a mistake in your labelling, but do check again, just to be sure.

Edit: BTW, do you have another voltmeter on hand that you could try? I do, and I have determined that they both provide the same voltage readings down to .01 volts. The incorrect readings might be caused by a number of factors. Faulty or poor-quality test equipment, faulty component(s) in the circuit, or human error come to mind. Oh, we know all about this...  (-;

Quote from: RG100ESROX on December 10, 2024, 10:00:55 AM

Quote from: Miyagi_83 on December 10, 2024, 04:32:41 AM

Quote from: RG100ESROX on November 25, 2024, 06:51:19 PM

Quote from: g1 on November 25, 2024, 03:37:05 PMThat's fine if you had the gen. set for low level output.
Check the amps power supply (DC)voltages, shown as  A,B,C,D,E on the schematic.

VOLTAGES REQUESTED: Here ya go!

A =  41.90VDC  = +41.18VDC
B = -41.60VDC  = -41.22VDC
C =  12.61VDC  = +12.45VDC
D = -12.60VDC  = -12.45VDC
E =  25.38VDC  =+25.19VDC

I found them. 2 weeks ago they were fine, so you might have made a mistake in your labelling, but do check again, just to be sure.

Edit: BTW, do you have another voltmeter on hand that you could try? I do, and I have determined that they both provide the same voltage readings down to .01 volts. The incorrect readings might be caused by a number of factors. Faulty or poor-quality test equipment, faulty component(s) in the circuit, or human error come to mind. Oh, we know all about this...  (-;

Here ya go!!!

Quote from: RG100ESROX on December 10, 2024, 02:41:28 PM Here ya go!!!

Thank you, sir.
I understand that point A is roughly the same as point B, only positive. This means it was simply mislabelled in the bias-string-voltage pic posted earlier. Therefore, I would like to kindly ask you to measure and write down the voltages along the bias string again, but please don't rush it, focus, and note down everything correctly so we don't spend time looking for solutions to non-existent problems.
Looking forward to it.
M.

Quote from: Miyagi_83 on December 10, 2024, 03:19:24 PM

Quote from: RG100ESROX on December 10, 2024, 02:41:28 PM Here ya go!!!

Thank you, sir.
I understand that point A is roughly the same as point B, only positive. This means it was simply mislabelled in the bias-string-voltage pic posted earlier. Therefore, I would like to kindly ask you to measure and write down the voltages along the bias string again, but please don't rush it, focus, and note down everything correctly so we don't spend time looking for solutions to non-existent problems.
Looking forward to it.
M.

No. Thank YOU!!

Will do. It'll be later this afternoon , but I'll take my time and get them posted as soon as possible.

Here are the bias string voltages.

As you can see...where I once had -.6 (as indicated on the schematic) is now +.521v. I don't even know how this is possible. But, this is the case.

Now, if I look at the back side of the PCB. I honestly do not see how the bias trim pot can be located in the circuit as indicated in the schematic. However, and again, I used to get -.6VDC on the bottom lug of the bias trim pot as it is indicated on the schematic before I broke the amp. So, how does it go from -.6VDC to +.521?

Anyway, let me know what you think, and if you need any further clarification or additional voltage readings.

Thanks in advance, M.

-Jay

Quote from: RG100ESROX on December 11, 2024, 01:27:02 PMAnyway, let me know what you think, and if you need any further clarification or additional voltage readings.

Jay, I'd like to ask you to measure voltages at the following points:
1. base and emitter of Q10
2. collector and emitter of Q11
3. collector and emitter of Q12

I suspect we'll need to rearrange the schematic.

Is there a meaning to the short red line below the trim pot and the red dot between the yellow-filled oval and Q12 on the schematic excerpt you posted?

Quote from: Miyagi_83 on December 11, 2024, 03:53:15 PMIs there a meaning to the short red line below the trim pot and the red dot between the yellow-filled oval and Q12 on the schematic excerpt you posted?

Yes. I was just denoting that I found it interesting that these two points in the circuit shared the same voltage reading....

Quote from: RG100ESROX on December 11, 2024, 04:31:45 PM

Quote from: Miyagi_83 on December 11, 2024, 03:53:15 PMIs there a meaning to the short red line below the trim pot and the red dot between the yellow-filled oval and Q12 on the schematic excerpt you posted?

Yes. I was just denoting that I found it interesting that these two points in the circuit shared the same voltage reading....

According to the schematic they are connected, so that's perfectly normal. In the measurements you took, however, the .52 V stands out because on paper it's the same spot, but in practice it looks like that part of the trim pot is tied to the base of Q11.