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

[RG100ESROX]

If I have hooked up the oscilloscope correctly...this is the waveform I'm getting.

It appears to be missing half the waveform....

Just FYI: I am getting the same reading across both  .6 ohm resistors.  (e.g.: 20.4mV across both .6 ohm resistors with the trim pot almost maxed) I have noticed that the amp sounds better with the higher readings.

Anyone have any idea why the trim pot is not adjusting the bias as it should? It worked in the past.

UPDATE: For some reason. When I plug an additional speaker cab in. The amp actually sounds better. The tone improves. Not so flubby, tighter bass. The volume does drop some when the second speaker cab is plugged in.
If this is the case. What could the issue be that is causing half the waveform to be missing?

[Tassieviking]

I presume you are measuring either the positive or negative side of the amp, one 0R6 resistor is on the positive rail and one is on the negative rail.
If you use a 2 channel cro and run the cro on both resistors you would find one half sinewave on each resistor.

[g1]

Are you scoping across resistors or at the amp output?

[RG100ESROX]

The amp speaker output.

Also, my clean channel isn't as clean as it should be...🤷 If this helps in the troubleshooting..?

[RG100ESROX]

I presume you are measuring either the positive or negative side of the amp, one 0R6 resistor is on the positive rail and one is on the negative rail.
If you use a 2 channel cro and run the cro on both resistors you would find one half sinewave on each resistor.

Interesting...and good to know. Thank you.

So, I'm guessing that if I were to scope both speakers outputs, I would see the other half of the sign wave on each of them...?

[RG100ESROX]

Well, my 6800uF 100v caps came today and they're installed. It did help with the bass response...

[RG100ESROX]

Well, I took a stab at it...I think I've got 1KHz injected at the input jack, with the Oscope connected at the speaker jack...

If I've done it right, this signwave looks terrible....

If I've done it correctly...what's next???

[saturated]

I don't think that is your signal because of your time constant is 5ms then I'm calculating about a 67 hz wave

What is the voltage Vp-p or RMS from your generator

[RG100ESROX]

Vpp:0.92V

[RG100ESROX]

Here are some pics of the sine wave....

The first pic is of the red channel - no clipping/no presence
The second pic is of the red channel - w/clipping/no presence
The third pic is of the red channel - w/clipping and presence

The sine wave did not change at all when adjusting the trim pot for the bias. Not sure if it was even supposed to....?

So, how do we bias this thing??

[saturated]

Based on a thread here in the forum. I should see 40/50mA across the two .6 ohm 10 watt resistors. However, I'm only seeing as high as 20mA with the bias pot nearly dimed clockwise.

However, it doesn't seem that the amp sounds like it should regardless of where I set the trim pot.

What am I missing here??

Any bias experts here in the forum regarding the Randall RG100-ES??

I don't know anything about biasing amps (I would like to...) but are supposed to measure the voltage drop to calculate current?  If so I did some calculations

You cannot view this attachment.

Seems like you weren't that far off if measuring mV and not mA

What did you get at each end of the adjustment 

[g1]

Post #24 shows a proper sinewave out for the clean channel.  It looks nothing like what you showed at post #15.
Are you still at the speaker out?  What changed to get a proper waveform?

[RG100ESROX]

Thank you very much, Saturated. Your math is very helpful.

I actually had the green channel completely shut off when I measured the red channel with the scope. Everything was at zero, with the clipping off. And you're right. I obviously did something wrong the first time I attempted to get a sign wave. This one looked like I expected it to.

Now, if I am supposed to get .40mA/50mA across both R.6 resistors, I probably can. With the trim pot almost maxed (if it isn't actually maxed), I can get about 30mV measured across the two .6 ohm resistors. But that just doesn't seem right for some reason. I mean, the trim pot came with the adjustment right in the middle at 9:00. And all of the photos that I can find online show other peoples boards with their trim pots set right about 8:00 to 9:00 o'clock. So, I obviously have something going on with my amp.

Now, I measured most of the test points based on the schematic, and they are all where they should be.

Question; I did a diode test on the TIP31 and the two TIP32's, and one of the TIP32's only read about .256. The other two were about .565. Which is what we would expect to see, correct? Maybe I got the reading I did because it's mounted to the board and some other component is throwing it off...?

If that's NOT the case, then the TIP32 that's the furthest right on my board is bad (see photo.)

Can anyone confirm these diode test readings? Or have I been drinking my own bath water again??  

[g1]

I don't know where that bias info came from but it sounds a bit suspect to me.
And the term 'both' resistors always leads to some confusion.  Sometimes it means 'each' and sometimes it means the 2 in series.
Better to just stick with measuring each and stating it that way.
Lots of amps bias with 10 to 20 mA current per output transistor.  10mA would be 6mV across each 0R6 resistor.  I think that may be sufficient to get out of crossover distortion, which is all we care about when biasing SS amps.  Any more than that will not help the tone in any way, and will run the output transistors hotter than they need to.
Set the bias to the minimum mV reading across each 0R6 (no signal applied).  What reading do you get?
Now get a nice clean sinewave at the output like the first pic in post #24, but with less amplitude, maybe 100mV peak to peak.  Do you still have a nice clean sinewave like that, or is there a crossover notch in the middle of the sinewave?
For solid-state amps, we just increase the bias til the crossover notch just disappears, no more is needed.

[RG100ESROX]

I don't know where that bias info came from but it sounds a bit suspect to me.
And the term 'both' resistors always leads to some confusion.  Sometimes it means 'each' and sometimes it means the 2 in series.
Better to just stick with measuring each and stating it that way.
Lots of amps bias with 10 to 20 mA current per output transistor.  10mA would be 6mV across each 0R6 resistor.  I think that may be sufficient to get out of crossover distortion, which is all we care about when biasing SS amps.  Any more than that will not help the tone in any way, and will run the output transistors hotter than they need to.
Set the bias to the minimum mV reading across each 0R6 (no signal applied).  What reading do you get?
Now get a nice clean sinewave at the output like the first pic in post #24, but with less amplitude, maybe 100mV peak to peak.  Do you still have a nice clean sinewave like that, or is there a crossover notch in the middle of the sinewave?
For solid-state amps, we just increase the bias til the crossover notch just disappears, no more is needed.

Great info!! Thank you.

It didn't even consider some of your points regarding the bias procedure.

I have four new power transistors showing up today. So, I'll give it another attempt after installing the new power transistors.

I'll send pics and info this afternoon.

And, I don't remember what my previous readings across the .6R resistors was. But I'll post the readings with the photos later.

Thanks again for the detailed reply. All good info.