Where to find 6000uF 50V replacement cap cans??

[RG100ESROX]

How important is it that the pot be a log (B) taper??? All I have at home are audio taper pots.

It's not going to explode if you use a log (A, audio) pot. The difference lies in the rate at which the resistive divider is formed as you turn the knob. In an ideal linear (B) potentiometer the resistance value will change, as the name suggests, linearly. A log potentiometer will reach about 10% of its value at 50% rotation. Do a search for 'log pot graph' / 'log pot curves' or something along those lines. A picture is worth a thousand words.

Oh, I understand the difference. I just wasn't sure if you had a technical reason for the linear pot request. I just wanted to be sure the audio taper would suffice.

When I get home Sunday or Monday. I'll get this gadget put together real quick and then send you a reply here, and you can respond when it's convenient.

Talk to ya then. Have a nice weekend.

-Jay

[g1]

The floating/dancing/jitter on the scope sounds like a triggering issue.  The scope should have a few choices for trigger source.  For example, some have norm, auto, or line to choose from.  Try the different trigger options and see if you can get the waveform to lock.

The waveform you posted before did not have any crossover distortion, and that was with the trimmer all the way down.  None of the other pics have shown any crossover notch either, so I would just leave the trimmer set to minimum.
I think maybe your meter is not accurate at the low mV levels, and maybe it is biased hotter than what the meter is showing.  Do you have access to a better quality meter to try?
When you hear hum that gets worse as you turn up the bias, that is probably due to increased loading of the power supply.  Proper bias levels should not add any kind of hum.
Crossover distortion would only be noticeable at very low volumes, like on the decay of a note.  It would sound like a bit of fizzyness or graininess.
Other than that, any audible effect you are hearing from changing the bias is due to loading down the power supply and making more 120Hz ripple, which modulates the signal in different ways.  So you don't ever want to adjust bias in a solid state amp by ear.

Here is a picture of the crossover notch, which I don't think you have had at any time with your amp.

You cannot view this attachment.

[phatt]

At RG100
From post11,
When you say;
  "It used to sound just like the tone in the Dokken 'Just Got Lucky' (guitar only) video."

Well there are a lot of things besides the amplifier that can alter the outcome.
so,,, the Q you need to ask yourself is,
What was your whole setup before it all went south?

Did you change speakers? Did you change PU's or electronics in guitar?
Many things besides an amplifier can easy rob you of sound quality.
Just changing speakers can alter tone in a DRAMATIC way. 4 G12's in a box will sound very different to a single G12 in an open back cab
Some speakers might flab more so that others.

At post 13;
You mentioned you have taken a speaker out of the Randell cab and mixed in another speaker. That will change the sound big time when compared to the original Quad setup.
How about going back to the setup you had BEFORE it went wrong,,,then start all over again.

Dirty or corroded connections can cause signal loss, guitar cords can slowly cause signal loss due to broken strands. It seems to me that you have made a false assumption,, ""as G1 has noted there is no crossover distortion.""
And besides biasing ANY amp hotter does not make for better tone.
A Bias pot is NOT a Friggin GAIN knob. It has nothing to do with the gain of the amp, it just sets the balance between the 2 output devices.

Yes there is a lot of hype regards to biasing Valve rigs hotter to get the Mojo sound. well they don't understand what they are talking about. I have shown a few players in real time the sonic result of hot verses cold bias.
Here is what happens, with hot bias the amp starts to break up on 4.
With cold bias it starts breakup on 7.
So hot or cold the amp sounds the same. only Q left to ask the owner is how often do you want to replace your power valves.

The SS amp design you have is not going to give you power amp Dirt or sag as they don't work the same way. Valve amps have a soft power supply while SS use a stiff rigid PSU but you can design them to sag a bit with some mods.

If the Amp is working,,,My advice, go back and Establish just where it all went wrong. Because it's a fair bet something else might be the culprit.
Phil.

[RG100ESROX]

The floating/dancing/jitter on the scope sounds like a triggering issue.  The scope should have a few choices for trigger source.  For example, some have norm, auto, or line to choose from.  Try the different trigger options and see if you can get the waveform to lock.

The waveform you posted before did not have any crossover distortion, and that was with the trimmer all the way down.  None of the other pics have shown any crossover notch either, so I would just leave the trimmer set to minimum.
I think maybe your meter is not accurate at the low mV levels, and maybe it is biased hotter than what the meter is showing.  Do you have access to a better quality meter to try?
When you hear hum that gets worse as you turn up the bias, that is probably due to increased loading of the power supply.  Proper bias levels should not add any kind of hum.
Crossover distortion would only be noticeable at very low volumes, like on the decay of a note.  It would sound like a bit of fizzyness or graininess. This is not what I am hearing. It's more like having too much distortion, and not the good kind.
Other than that, any audible effect you are hearing from changing the bias is due to loading down the power supply and making more 120Hz ripple, which modulates the signal in different ways.  So you don't ever want to adjust bias in a solid state amp by ear.

Here is a picture of the crossover notch, which I don't think you have had at any time with your amp.

You cannot view this attachment.

The floating/dancing/jitter on the scope sounds like a triggering issue.  The scope should have a few choices for trigger source.  For example, some have norm, auto, or line to choose from.  Try the different trigger options and see if you can get the waveform to lock.
I do have a couple of choices for the trigger. I will try them and see if the sine wave stops moving around.

The waveform you posted before did not have any crossover distortion, and that was with the trimmer all the way down.  None of the other pics have shown any crossover notch either, so I would just leave the trimmer set to minimum. Will do. I'll leave the trim pot set to FCCW.
I think maybe your meter is not accurate at the low mV levels, and maybe it is biased hotter than what the meter is showing.  Do you have access to a better quality meter to try?
No. I wish I did, but I don't.
When you hear hum that gets worse as you turn up the bias, that is probably due to increased loading of the power supply.  Proper bias levels should not add any kind of hum.
Crossover distortion would only be noticeable at very low volumes, like on the decay of a note.  It would sound like a bit of fizzyness or graininess.
Other than that, any audible effect you are hearing from changing the bias is due to loading down the power supply and making more 120Hz ripple, which modulates the signal in different ways.  So you don't ever want to adjust bias in a solid state amp by ear. Understood. Thank you.

Here is a picture of the crossover notch, which I don't think you have had at any time with your amp. I did have this notch in my sine wave at one point, and it looked just like your illustration. If I adjusted the bias about 5mA or so, it would go away. Why I no longer have it is beyond me. If it reappears, I'll take a photo and post it here. Thank you for all of the great info and illustration. Much appreciated. I should be home by tomorrow evening. Is there anything specific you want me to try when I get home? I am going to try 'Miyagi's' suggestion using the trim pot and injecting the sine wave at the FX return jack. If you'd rather I not try this, please let me know. Otherwise I'll go ahead with it.

[RG100ESROX]

At RG100
From post11,
When you say;
  "It used to sound just like the tone in the Dokken 'Just Got Lucky' (guitar only) video."

Well there are a lot of things besides the amplifier that can alter the outcome.
so,,, the Q you need to ask yourself is,
What was your whole setup before it all went south?

Did you change speakers? Did you change PU's or electronics in guitar?
Many things besides an amplifier can easy rob you of sound quality.
Just changing speakers can alter tone in a DRAMATIC way. 4 G12's in a box will sound very different to a single G12 in an open back cab
Some speakers might flab more so that others.

At post 13;
You mentioned you have taken a speaker out of the Randell cab and mixed in another speaker. That will change the sound big time when compared to the original Quad setup.
How about going back to the setup you had BEFORE it went wrong,,,then start all over again.

Dirty or corroded connections can cause signal loss, guitar cords can slowly cause signal loss due to broken strands. It seems to me that you have made a false assumption,, ""as G1 has noted there is no crossover distortion.""
And besides biasing ANY amp hotter does not make for better tone.
A Bias pot is NOT a Friggin GAIN knob. It has nothing to do with the gain of the amp, it just sets the balance between the 2 output devices.

Yes there is a lot of hype regards to biasing Valve rigs hotter to get the Mojo sound. well they don't understand what they are talking about. I have shown a few players in real time the sonic result of hot verses cold bias.
Here is what happens, with hot bias the amp starts to break up on 4.
With cold bias it starts breakup on 7.
So hot or cold the amp sounds the same. only Q left to ask the owner is how often do you want to replace your power valves.

The SS amp design you have is not going to give you power amp Dirt or sag as they don't work the same way. Valve amps have a soft power supply while SS use a stiff rigid PSU but you can design them to sag a bit with some mods.

If the Amp is working,,,My advice, go back and Establish just where it all went wrong. Because it's a fair bet something else might be the culprit.
Phil.

At RG100
From post11,
When you say;
  "It used to sound just like the tone in the Dokken 'Just Got Lucky' (guitar only) video."

Well there are a lot of things besides the amplifier that can alter the outcome.
so,,, the Q you need to ask yourself is,
What was your whole setup before it all went south? That's easy. G10, V4, T10, M7, B4, P10. Single 12" V-30 and a single 12" G12M70 from the original Randall 4x12 cab.

Did you change speakers? No. Same speaker and speaker cable. Did you change PU's or electronics in guitar? No. Unchanged.
Many things besides an amplifier can easy rob you of sound quality.
Just changing speakers can alter tone in a DRAMATIC way. 4 G12's in a box will sound very different to a single G12 in an open back cab
Some speakers might flab more so that others.

At post 13;
You mentioned you have taken a speaker out of the Randell cab and mixed in another speaker. That will change the sound big time when compared to the original Quad setup. The amp is setup exactly like it was before I broke the amp. So, nothing is different now than it was when the amp was functioning okay previously.
How about going back to the setup you had BEFORE it went wrong,,, I'm already there.then start all over again.
What went wrong was me. I was taking some readings in the amp, and instead of grounding the signal generator to the chassis. I used the input jacks ground. Pretty stupid on my part, because the input jacks ground was grounded to the input itself. This drew some pretty good current and blew a trace on the back of the board in the power amp section. Ever since them, we've been trying to find out what I broke exactly and fix it. At this point the amp is somewhat functional. With the exception of, the tone is too gainy, and I get a noticeable hum that increases with any increase in the bias adjustment. For the reasons g1 pointed out in the second to last post.
Dirty or corroded connections can cause signal loss, guitar cords can slowly cause signal loss due to broken strands. It seems to me that you have made a false assumption,, ""as G1 has noted there is no crossover distortion."" I have cleaned all of the jacks in the amp and inspected all cabling, speakers and the guitar.
And besides biasing ANY amp hotter does not make for better tone. This is true. I understand this.
A Bias pot is NOT a Friggin GAIN knob. It has nothing to do with the gain of the amp, it just sets the balance between the 2 output devices. You're preaching to the choir, Phil. (-;

Yes there is a lot of hype regards to biasing Valve rigs hotter to get the Mojo sound. Which I am also aware of, as most of my Amps ARE valve Amps. well they don't understand what they are talking about. I have shown a few players in real time the sonic result of hot verses cold bias.
Here is what happens, with hot bias the amp starts to break up on 4.
With cold bias it starts breakup on 7.
So hot or cold the amp sounds the same. only Q left to ask the owner is how often do you want to replace your power valves.

The SS amp design you have is not going to give you power amp Dirt or sag as they don't work the same way. Correct. This I understand. Valve amps have a soft power supply while SS use a stiff rigid PSU but you can design them to sag a bit with some mods.

If the Amp is working,,,My advice, go back and Establish just where it all went wrong. Because it's a fair bet something else might be the culprit.
Phil. Thank you, Phil. I have explained what the issue is now with the amp at the beginning of this post. The amp is broken because I broke it. How I broke it is explained above. This is what we are troubleshooting at this point.

[phatt]

Thanks Jay (I assume) I appreciate the effort you have gone to, to explain it all.
I know it must be very frustrating for you.

I had a hair line crack hidden under a solder pad in an amp that drove me nuts for a very long time. It was by chance that I turned the amp on just before I turned on the bench light one evening and saw a tiny flash on the circuit board which led me to the answer to the intermittent bad hum.
The crack was one of the main filter caps solder joints. The slightly over filled solder was covering the Crack in the copper track.
Phil.

[RG100ESROX]

Thanks Jay (I assume) I appreciate the effort you have gone to, to explain it all.
I know it must be very frustrating for you.

I had a hair line crack hidden under a solder pad in an amp that drove me nuts for a very long time. It was by chance that I turned the amp on just before I turned on the bench light one evening and saw a tiny flash on the circuit board which led me to the answer to the intermittent bad hum.
The crack was one of the main filter caps solder joints. The slightly over filled solder was covering the Crack in the copper track.
Phil.

I think "frustrated" is an understatement, Phil. (-;

Because I had blown a trace on my board. I suspected the same thing. So, I meticulously checked every connection on the front and back of the board to be sure each component was connected to the next. I feel pretty confident that this is not my issue, because the amp wouldn't be as operable as it is if this were the case.

Aside from the increase in hum that I get when the bias is increased, and the awful  distortion on top of my tone. The amp is pretty much functional.

Since determining that the preamp section of my amp is fine. My issue is confined to the power section only. There really aren't too many components that could be the issue. And on top of that, most of the components in the power section have been replaced.

I may be a little too optimistic here, but I feel confident that we will be able to isolate and identify the issue soon...I hope. And, with all of the brains involved. How could we not? 

[RG100ESROX]

I expected to be home by now, but, my dad took a nasty fall yesterday. So, I will be staying with the folks a little longer than expected.

However, I will be running home tomorrow morning to retrieve my amp, soldering station and tools, so that we can continue this adventure without too much delay.

Thanks for everyone's patience, guidance and help. Most appreciated.

-Jay

[Miyagi_83]

I expected to be home by now, but, my dad took a nasty fall yesterday. So, I will be staying with the folks a little longer than expected.

However, I will be running home tomorrow morning to retrieve my amp, soldering station and tools, so that we can continue this adventure without too much delay.

Thanks for everyone's patience, guidance and help. Most appreciated.

-Jay

Good luck with the amp and, most importantly, all the best to your dad!

[RG100ESROX]

The floating/dancing/jitter on the scope sounds like a triggering issue.  The scope should have a few choices for trigger source.  For example, some have norm, auto, or line to choose from.  Try the different trigger options and see if you can get the waveform to lock.

The waveform you posted before did not have any crossover distortion, and that was with the trimmer all the way down.  None of the other pics have shown any crossover notch either, so I would just leave the trimmer set to minimum.
I think maybe your meter is not accurate at the low mV levels, and maybe it is biased hotter than what the meter is showing.  Do you have access to a better quality meter to try?
When you hear hum that gets worse as you turn up the bias, that is probably due to increased loading of the power supply.  Proper bias levels should not add any kind of hum.
Crossover distortion would only be noticeable at very low volumes, like on the decay of a note.  It would sound like a bit of fizzyness or graininess. This is not what I am hearing. It's more like having too much distortion, and not the good kind.
Other than that, any audible effect you are hearing from changing the bias is due to loading down the power supply and making more 120Hz ripple, which modulates the signal in different ways.  So you don't ever want to adjust bias in a solid state amp by ear.

Here is a picture of the crossover notch, which I don't think you have had at any time with your amp.

You cannot view this attachment.

The floating/dancing/jitter on the scope sounds like a triggering issue.  The scope should have a few choices for trigger source.  For example, some have norm, auto, or line to choose from.  Try the different trigger options and see if you can get the waveform to lock.
I do have a couple of choices for the trigger. I will try them and see if the sine wave stops moving around.

The waveform you posted before did not have any crossover distortion, and that was with the trimmer all the way down.  None of the other pics have shown any crossover notch either, so I would just leave the trimmer set to minimum. Will do. I'll leave the trim pot set to FCCW.
I think maybe your meter is not accurate at the low mV levels, and maybe it is biased hotter than what the meter is showing.  Do you have access to a better quality meter to try?
No. I wish I did, but I don't.
When you hear hum that gets worse as you turn up the bias, that is probably due to increased loading of the power supply.  Proper bias levels should not add any kind of hum.
Crossover distortion would only be noticeable at very low volumes, like on the decay of a note.  It would sound like a bit of fizzyness or graininess.
Other than that, any audible effect you are hearing from changing the bias is due to loading down the power supply and making more 120Hz ripple, which modulates the signal in different ways.  So you don't ever want to adjust bias in a solid state amp by ear. Understood. Thank you.

Here is a picture of the crossover notch, which I don't think you have had at any time with your amp. I did have this notch in my sine wave at one point, and it looked just like your illustration. If I adjusted the bias about 5mA or so, it would go away. Why I no longer have it is beyond me. If it reappears, I'll take a photo and post it here. Thank you for all of the great info and illustration. Much appreciated. I should be home by tomorrow evening. Is there anything specific you want me to try when I get home? I am going to try 'Miyagi's' suggestion using the trim pot and injecting the sine wave at the FX return jack. If you'd rather I not try this, please let me know. Otherwise I'll go ahead with it.

Just FYI: When I went home this evening to grab the amp and tools. I hooked the amp up to the scope real quick, and initially the sine wave was pretty erratic and unstable. But as soon as I plugged the 8 ohm dummy load into the speaker jack. The sine wave calmed right down and I had a nice steady sine wave on the scope.   

Also, the amp is somewhat functional. We just need to figure out what's causing the extra unwanted distortion. The sine wave showed no sign of Xover, so It has to be something else that's causing this issue. But what? What in the power section would/could be the cause? The transistors are all new. Most of the resistors are new. I've meticulously checked continuity between all of the components on the board front and back based on the schematic. It's probably staring me right in the face, and I can't see the Forrest though the trees.   

So, if anyone would care to chime in. I will have the amp and equipment/tools all setup and ready by noon today.

Thanks again to everyone for your time, knowledge and patience.

-Jay

[Miyagi_83]

Also, the amp is somewhat functional. We just need to figure out what's causing the extra unwanted distortion. The sine wave showed no sign of Xover, so It has to be something else that's causing this issue. But what? What in the power section would/could be the cause? The transistors are all new. Most of the resistors are new. I've meticulously checked continuity between all of the components...

Just a thought, have you tried a different speaker cabinet? Is there nothing rattling in your guitar, amp, or cab?

[RG100ESROX]

Also, the amp is somewhat functional. We just need to figure out what's causing the extra unwanted distortion. The sine wave showed no sign of Xover, so It has to be something else that's causing this issue. But what? What in the power section would/could be the cause? The transistors are all new. Most of the resistors are new. I've meticulously checked continuity between all of the components...

Just a thought, have you tried a different speaker cabinet?

Yes. A 12" V-30 ext., 12" G12M70 ext. and a 4x12 with half V-30 and GB's.

[Miyagi_83]

Ok, so it's not the speaker. What about mechanical rattle in the amplifier's chassis or guitar?

[RG100ESROX]

Ok, so it's not the speaker. What about mechanical rattle in the amplifier's chassis or guitar?

Guitar is all good. Played through other Amps and it sounds great.

[Miyagi_83]

Is there a chance you could record the distortion in question, so we know what we're talking about?