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

[RG100ESROX]

Do not proceed with signal if you have a problem with idle current (no signal).
Get that sorted out first.
Disconnect anything plugged in to input or FX return.
It is critical that the (-) side of the output jack does not get connected to chassis ground (because R63).  Sometimes the test equipment can do this.
Make sure there is no DC at the output.  If so connect the speaker.
With no signal, do you hear much hum?  Does the idle current through the emitter resistors rise?

As Miyagi stated above, when the amp is running properly, delivering power to the load will increase the current through the output transistors.  This is normal, and not idle current, but working current.

AND...we're injecting the signal in at the FX return

This shouldn't make a difference other than the signal being processed (amplified, clipped, shaped etc.) when going through the preamplifier. You can plug your guitar straight into the loop return and play it like that, no problem. Not that you will like the results, but you can. I have done this a number of times.

Did you build that attenuator to control the signal level going into the return jack?

Also, do you have another dummy load resistor to try?

Have you tried playing the amp at your parents' house before you took those alarming measurements?

If I remove the dummy load. The idle current with or without an injected signal is about 5mV.

If I understand it correctly, when you inject a signal, it's no longer idle. Idle is when NO SIGNAL is being applied, so the device is not amplifying anything except noise, it's idle.
When you put a signal in, the output devices will conduct, so the current through the output devices and anything in series with them will rise. Correct me if I'm wrong, anyone.

Q:Have you tried playing the amp at your parents' house before you took those alarming measurements? YES. I RECORDED A SOUND DEMO OF THE DISTORTION I AM GETTING FROM THE AMP. TRUST ME, SOME MIGHT SAY IT SOUNDS FINE, BUT IT'S NOT. IT'S THE BAD KIND OF DISTORTION SITTING ON TOP OF THE GOOD DISTORTION.


Q:Did you build that attenuator to control the signal level going into the return jack?
I'M SORRY...I COMPLETELY FORGOT ABOUT THIS THING. MY APOLOGIES. I WILL NEED TO BUILD IT. SO, NO, IT WAS NOT USED WHEN INJECTING THE SIGNAL INTO THE FX RETURN. ONCE I HAVE THE POT BUILT, I'LL TRY THIS AGAIN AND GET BACK TO YA. THIS IS WHY THE IDLE BIAS CURRENT WAS SO DAMN HIGH. GEEEEEEEZE....


Q:Also, do you have another dummy load resistor to try?
I DO NOT. JUST THE ONE.

[RG100ESROX]

Do not proceed with signal if you have a problem with idle current (no signal).
Get that sorted out first.

I FAILED TO USE THE ATTENUATOR WHEN INJECTING THE SIGNAL INTO THE FX RETURN. THIS IS WHY THE IDLE CURRENT WAS SO HIGH.


Disconnect anything plugged in to input or FX return. DONE.
It is critical that the (-) side of the output jack does not get connected to chassis ground (because R63).  Sometimes the test equipment can do this. NOTED.
Make sure there is no DC at the output.  If so connect the speaker.
With no signal, do you hear much hum?  Does the idle current through the emitter resistors rise? I WILL CHECK THIS AND POST BACK.

As Miyagi stated above, when the amp is running properly, delivering power to the load will increase the current through the output transistors.  This is normal, and not idle current, but working current. THIS QUESTION IS FOR MY INFO. WHAT KIND OF CURRENT ARE WE TALKING ABOUT HERE? WHAT'S TYPICAL AT SAY A HIGH BEDROOM LEVEL VOLUME?

[RG100ESROX]

I don't know if this is valuable information or not, but I'll convey anyway.

I connected the SG (.1mV/1KHz.) at the input (this is without the 22R resistor reinstalled), and the Oscope at the speaker out. With the bias trim set FCCW my bias was 8mV, and there was an indication of Xover distortion in the sine wave (see first photo below.)

At about 13mV the Xover distortion seems to disappear.

For what it's worth. I reinstalled the 22R resistor in series with the bias trim pot, and then looked at the bias current. At FCCW my bias was 6mV. At FCW my bias had adjusted to 8mV.

Now, this was with a guitar plugged in and a speaker. If you remember, we got no bias current at all unless we disconnected the 22R resistor using the Signal Generator. Not sure why this makes a difference. Maybe the input signal was too low to give us a bias reading???

I don't know if this is any kind of an indication for you guys, but just in case, this is why I'm sharing this...

I will inject a signal of .1mV/1KHz at the FX return using the resistor sub box (see drawing below of resistor sub box use. Let me know if there are issues with this config.) and let you know if I can get a clean sine wave at full power. And when you say full power. I am assuming this means with the gain and volume set to 10??? Correct??

Also, I triple checked, and with the phono plug plugged into the FX RETURN jack. The ground connection that connects to the tip, is completely disconnected with the phono plug plugged into the FX return jack.

[Miyagi_83]

Q:Also, do you have another dummy load resistor to try?
I DO NOT. JUST THE ONE (disregard how you see the dummy Load box connected in the photo. it's for the image of the box only.)

I asked that question because you'd said that your current readings were too high at ZERO signal, so I figured there might have been something wrong with the dummy load. Because you took what looks to be correct (based on info from this thread) readings later on, it seems the DL is fine and you had most likely taken those alarming readings with signal in. (Although at some point you did write that the current jumped up WITH AND WITHOUT signal applied, so I'm confused).

Therefore, I encourage you to refrain from using the term IDLE CURRENT for the time being because you sometimes tend to apply it to working / under-signal conditions. I can't speak for other people here, but it gets me confused more than it should. It is critical to be as precise as possible and post all necessary details, such as whether the generator is on or off, where it's plugged in, signal level, possible attenuation etc. As sir Francis Bacon put it, 'The ill and unfit choice of words wonderfully obstructs the understanding.' I have been guilty of it a few times in my life too.

I AM ASSUMING THAT THIS WILL WORK IN PLACE OF THE 22K POT THAT I WAS SUPPOSED TO BUILD...? I BROUGHT MY RESISTOR SUBSTITUTION BOX WITH ME. I'LL START OUT AT THE 1M, AND ADJUST ACCORDINGLY FOR THE OUTPUT SIGNAL INJECTED AT THE FX RETURN?? AND YES, I AM GOING TO HAVE TO DO SOME CREATIVE WIRING IN ORDER TO USE THE SUBSTITUTION BOX.

I would add a resistor in series between the signal generator and the resistor box so as to have a resistive divider. Diagram attached.

YES. I RECORDED A SOUND DEMO OF THE DISTORTION I AM GETTING FROM THE AMP. TRUST ME, SOME MIGHT SAY IT SOUNDS FINE, BUT IT'S NOT. IT'S THE BAD KIND OF DISTORTION SITTING ON TOP OF THE GOOD DISTORTION.

I listened to it and, you're right, I can't hear it. Can this nasty distortion be heard on cleans too? If possible, could you plug your guitar in to the FX return and play it to see if it's there? You might have to use the volume knob on your axe to control the loudness.
**Do it only when you have gotten your bias right. You don't want to damage your amp.

The ground connection that connects to the tip, is completely disconnected with the phono plug plugged into the FX return jack.

I have already pointed out that the tip of the RETURN jack is NOT grounded with nothing plugged in. It's connected to the preamp out. Your front-end input jack is tied to ground with nothing plugged in. See the schematic attached.

[Miyagi_83]

YES. I RECORDED A SOUND DEMO OF THE DISTORTION I AM GETTING FROM THE AMP. TRUST ME, SOME MIGHT SAY IT SOUNDS FINE, BUT IT'S NOT. IT'S THE BAD KIND OF DISTORTION SITTING ON TOP OF THE GOOD DISTORTION.

I've listened to your demo again just now. I'd like to ask you to post your preamp settings for it, if possible of course.

EDIT: Also, as difficult as it may be to do using words, could you please describe the distortion you hear?

[RG100ESROX]

YES. I RECORDED A SOUND DEMO OF THE DISTORTION I AM GETTING FROM THE AMP. TRUST ME, SOME MIGHT SAY IT SOUNDS FINE, BUT IT'S NOT. IT'S THE BAD KIND OF DISTORTION SITTING ON TOP OF THE GOOD DISTORTION.

I've listened to your demo again just now. I'd like to ask you to post your preamp settings for it, if possible of course.

EDIT: Also, as difficult as it may be to do using words, could you please describe the distortion you hear?

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

The distortion I'm hearing sounds like if you took a distortion pedal, and on top of a good sounding amp with the gain set to 10, you add just a tad bit more distortion on top of the amps gain, and it sounds like you've turned the gain up just a little too much to the point where it no longer sounds good any longer. It's just too much distortion. The only other way I know of describing this distortion is, kind of like Xover distortion. It does not sound like a good distortion while you're playing. It's just....too much distortion.

Sorry, it's just one of those things that's hard to describe, but we all know what 'Good' distortion sounds like. Well, this is just too much distortion to sound good.

I will record a sound clip of the clean channel with the settings where they should render a nice clean tone, and we'll see if there is any distortion detected at these settings.

[Miyagi_83]

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

The distortion I'm hearing sounds like if you took a distortion pedal, and on top of a good sounding amp with the gain set to 10, you add just a tad bit more distortion on top of the amps gain, and it sounds like you've turned the gain up just a little too much to the point where it no longer sounds good any longer. It's just too much distortion. The only other way I know of describing this distortion is, kind of like Xover distortion. It does not sound like a good distortion while you're playing. It's just....too much distortion.

Sorry, it's just one of those things that's hard to describe, but we all know what 'Good' distortion sounds like. Well, this is just too much distortion to sound good.

I understand it's not easy to describe tone in words. You've done a pretty good job anyway, afaic.

Another question, how are YOU (you specifically) realizing channel switching?
*Looking at the schematic, the switching works by simply shunting either channel's output to ground, so only one of them puts out signal.

[RG100ESROX]

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

The distortion I'm hearing sounds like if you took a distortion pedal, and on top of a good sounding amp with the gain set to 10, you add just a tad bit more distortion on top of the amps gain, and it sounds like you've turned the gain up just a little too much to the point where it no longer sounds good any longer. It's just too much distortion. The only other way I know of describing this distortion is, kind of like Xover distortion. It does not sound like a good distortion while you're playing. It's just....too much distortion.

Sorry, it's just one of those things that's hard to describe, but we all know what 'Good' distortion sounds like. Well, this is just too much distortion to sound good.

I understand it's not easy to describe tone in words. You've done a pretty good job anyway, afaic.

Another question, how are YOU (you specifically) realizing channel switching?
*Looking at the schematic, the switching works by simply shunting either channel's output to ground, so only one of them puts out signal.

I'm using the Footswitch that came with the amp to switch channels.

[RG100ESROX]

Well, something has changed. I don't know what, but...I cannot turn the Variac up much past 7 volts with a speaker or dummy Load plugged in because the voltage measured across the .62R resistor starts to increase rapidly. At just 7VAC the voltage measured at the .62R resistor is about 10~12mV. This is without a signal injected.

So, something has changed, but what?

This didn't happen before I tried injecting a signal at the FX return jack. Coincidence? Maybe..

[Miyagi_83]

Bad solder joint somewhere?

EDIT: I don't see how injecting signal into the effects loop return could have done any damage. After all, that's where your effects go in if you use any. Also the preamp out is internally connected to it so...

[g1]

Like Miyagi stated, idle current is with nothing plugged in to any input.  So you do not need to check voltage across those resistors any time a signal is applied.

Your load box is connecting the amp output jack to chassis ground, via the scope BNC connecter.  That is bad as it shorts out R63, which is part of the feedback loop and will affect the sound.  It may also cause instability which could be messing with the idle current.

Use your scope probe.  Connect scope ground to chassis, and the scope probe to the red binding post on your load box.
When bringing up the voltage with variac, you may get idle current surges like that acros the 0R62's until it reaches a stable voltage.  Are you sure it was not doing that before?

[RG100ESROX]

Like Miyagi stated, idle current is with nothing plugged in to any input.  So you do not need to check voltage across those resistors any time a signal is applied.

Your load box is connecting the amp output jack to chassis ground, via the scope BNC connecter.  That is bad as it shorts out R63, which is part of the feedback loop and will affect the sound.  It may also cause instability which could be messing with the idle current.

Use your scope probe.  Connect scope ground to chassis, and the scope probe to the red binding post on your load box.
When bringing up the voltage with variac, you may get idle current surges like that acros the 0R62's until it reaches a stable voltage.  Are you sure it was not doing that before?

I have been using both probes from the scope and SG when taking readings.

And I thought about what you said regarding the current surges. I noticed this before at about 45VAC when using the 100 watt lightbulb. At about 50VAC the light bulb would go out.

So, I'm guessing that if I were to bring the amp up to voltage, and then plug the dummy load/speaker in...it should be okay if this is indeed the case. Correct??

I measured the DC at the speaker output jacks, and it read -.88mV...

[Miyagi_83]

I measured the DC at the speaker output jacks, and it read -.88mV...

Did you take this reading just now? If so, I understand that you put the theory to the test and it turned out to be true, right?

[RG100ESROX]

I measured the DC at the speaker output jacks, and it read -.88mV...

Did you take this reading just now? If so, I understand that you put the theory to the test and it turned out to be true, right?

The DCV reading on the output was earlier today.

Of course you were right about the high bias reading while bringing the supply voltage up, because I did not plug the signal into the FX return until the amp was up to voltage, and it was as expected.

I just now took some readings with the signal injected into the FX Return Jack.
all settings at zero
8ohms dummy load
signal .1mV/1KHz
Sine wave (is it just me, or does this sine wave look pretty bad? Is that cover distortion we're seeing?)
bias reading with signal 9.8mV
bias reading without a signal 3.2mV

When you said to take these readings at "Full Power"....how do I do that since the front panel controls do not function while we're plugged into the FX return jack. Do I just increase the signal level? If so, to what level? How many volts? I'm not clear on this.

[Miyagi_83]

how do I do that since the front panel controls do not function while we're plugged into the FX return jack. Do I just increase the signal level? If so, to what level? How many volts? I'm not clear on this

First, bias should be right so there's no crossover. Once that is done, and, if I remember well, it is, move on to the next steps.

Btw, did you place that resistor in series with the signal generator like I suggested earlier, in reply #258?

Do this experiment:
Unplug your signal and resistor box combo from the amplifier. Disconnect your scope from the amp too, just in case.
Now, hook up your scope probe to the output of the SG / resistance box, the point where it says 'to plug' on the diagram I posted in reply #258.
Set the signal level on your generator to, say, 1V. What can you see on the scope screen?
Now change the resistor value on the substitution box. What can you see on the scope? Try again and look at the scope.
 
This is your makeshift volume control now. Use it to adjust the signal going into the amp's return jack. Then, on your oscilloscope, watch the waveform coming out of the speaker jack and see when clipping starts. Full clean power is just before the onset of clipping, as I understand it. Then post the signal voltage needed to get there, as requested by g1.