Guess what?

Cadorman said:
Is your wall voltage swinging?
Click to expand...
That's entirely possible, but we have extremely clean power in this area.
Either way, they are swinging only slightly, and staying together. I just made a minor tweak and it's back at 78.1 one one side and 78.4 on the other. Will check again in a bit.
 
mcblink said:
That's entirely possible, but we have extremely clean power in this area.
Either way, they are swinging only slightly, and staying together. I just made a minor tweak and it's back at 78.1 one one side and 78.4 on the other. Will check again in a bit.
Click to expand...
Put the meter away and just crank it up. I can just imagine you waiting for the oven to heat up when you have the munchies and need to make a frozen pizza.
 
mcblink said:
Question out of curiosity:

What is "normal" bias "drift"/swing?

Not that I'm having a problem, but during operation I do notice some slight up and down changes, but it's not extreme, and as I understand it, it's normal...but how much swing is too much??

My amp is swinging anywhere from 78mV to about 82mV after setting it to 80, for reference...
Click to expand...
Try setting the master volume to zero, then see if it still swings up and down.
Please tell us what happens.

It does this on both sides at the same time? Or just one side?
 
Amp Mad Scientist said:
Try setting the master volume to zero, then see if it still swings up and down.
Please tell us what happens.

It does this on both sides at the same time? Or just one side?
Click to expand...
It happening both sides simultaneously, they swing in tandem and don't deviate from each other, and they haven't gone lower than 77.something are higher than 81.8-ish...
 
so from 6:30-ish to about...now (10:15-ish) it's remained steady, aside from small fluctuations. Nothing too extreme, just a mV or two. In relation to each other, they fluctuate consistently. In other words, if the right side goes up a tad, the left side goes up a tad. And vice-versa.

I think we're probably good here?

@Amp Mad Scientist
No MV here, each channel has it's own.
I borrowed my buddy's TSL602 once, it had a MV...but this 100w head doesn't.
I would assume in this case I turn all the volumes down and test all 3 channels?
If it matters, the bias voltage doesn't seem to change across the channels, I did look for that....no discernable diff.
I did not check if the vol knob positions on any channels had any affect.
 
mcblink said:
so from 6:30-ish to about...now (10:15-ish) it's remained steady, aside from small fluctuations. Nothing too extreme, just a mV or two. In relation to each other, they fluctuate consistently. In other words, if the right side goes up a tad, the left side goes up a tad. And vice-versa.

I think we're probably good here?

@Amp Mad Scientist
No MV here, each channel has it's own.
I borrowed my buddy's TSL602 once, it had a MV...but this 100w head doesn't.
I would assume in this case I turn all the volumes down and test all 3 channels?
If it matters, the bias voltage doesn't seem to change across the channels, I did look for that....no discernable diff.
I did not check if the vol knob positions on any channels had any affect.
Click to expand...
The circuit board is new?
 
[/QUOTE="mcblink, post: 306303, member: 325"]
That's entirely possible, but we have extremely clean power in this area.
Either way, they are swinging only slightly, and staying together. I just made a minor tweak and it's back at 78.1 one one side and 78.4 on the other. Will check again in a bit.
[/QUOTE]
I think it's fine. The power tubes are new.
 
mcblink said:
so from 6:30-ish to about...now (10:15-ish) it's remained steady, aside from small fluctuations. Nothing too extreme, just a mV or two. In relation to each other, they fluctuate consistently. In other words, if the right side goes up a tad, the left side goes up a tad. And vice-versa.

I think we're probably good here?

@Amp Mad Scientist
No MV here, each channel has it's own.
I borrowed my buddy's TSL602 once, it had a MV...but this 100w head doesn't.
I would assume in this case I turn all the volumes down and test all 3 channels?
If it matters, the bias voltage doesn't seem to change across the channels, I did look for that....no discernable diff.
I did not check if the vol knob positions on any channels had any affect.
Click to expand...

Do you know how to monitor the B+ voltage?
Leave the meter attached and see if the B+ voltage is fluctuating up and down too.
Let's see how much it drifts.

Please don't electrocute yourself.
I would feel bad if you died. But (don't worry) you will be immortalized into the Tone Rooms hall of fallen stars; remembered for your extraordinary bravery and sacrifice in the face of meandering bias drift measurements.
(like taking pictures inside a volcano, 30 seconds before it explodes)
You would not be soon forgotten, at least for a while.

I have seen things like this happen and I suspect it's caused by a slightly leaky capacitor in the bias power supply.
Since it's happening on both sides at the same time, it must be something common to both sides.
Does it seem to go up and down at regular intervals? Like it's timing out?

If you see this happening on only 1 side, I start to suspect a slightly leaky PI decoupling capacitor.

But look...
a capacitor can charge up and discharge at regular intervals when there is resistance across it...maybe that's what's happening. A very slow oscillation in a power supply.
 
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Word to the wise I've had a rash of amps damaged by voltage spikes. It starts with a blown fuse and if it has a thermistor cooked on the
primary side of the power transformer and it takes out the power transformer B+ secondary could be a CME from the Sun or the power company
Getting amps from all over the State with this issue I'm telling my customers to buy Furman power conditioners cheap insurance.

Years ago I had a contract with the cruse ships they own thousands of amps Mesa's were the worst over 1100 cooked PCB's the Fender amps died the same
death Mesa and Fender would not sell the PCB's so I made them it averaged out to $550.00 per amp in parts and they paid 120 days after the amps were
delivered fixed it got out of hand I'm not that rich. You guys are lucky AMS takes his time to help you time is money.
 
67plexi said:
You guys are lucky AMS takes his time to help you.
Click to expand...
Absolutely, and we're all grateful for it.
There are some people in this world that are genuinely happy to do kind and generous things for others out of the goodness of their hearts, instead of being purely driven by profit. Those are the kind of people that I respect the most. And yeah, we're lucky to have him around.
 
Amp Mad Scientist said:
Do you know how to monitor the B+ voltage?
Leave the meter attached and see if the B+ voltage is fluctuating up and down too.
Let's see how much it drifts.

Please don't electrocute yourself.
I would feel bad if you died. But (don't worry) you will be immortalized into the Tone Rooms hall of fallen stars; remembered for your extraordinary bravery and sacrifice in the face of meandering bias drift measurements.
(like taking pictures inside a volcano, 30 seconds before it explodes)
You would not be soon forgotten, at least for a while.

I have seen things like this happen and I suspect it's caused by a slightly leaky capacitor in the bias power supply.
Since it's happening on both sides at the same time, it must be something common to both sides.
Does it seem to go up and down at regular intervals? Like it's timing out?

If you see this happening on only 1 side, I start to suspect a slightly leaky PI decoupling capacitor.

But look...
a capacitor can charge up and discharge at regular intervals when there is resistance across it...maybe that's what's happening. A very slow oscillation in a power supply.
Click to expand...
I actually don't know anything about monitoring b+ voltage,....but if it's as simple as watching the voltage in pins 3 an 4 all sockets or something like that,, I can do it... The meter I was using yesterday doesn't have any clips on the test leads....so either I can try to rig something up with a couple of roach clips, or I borrow LRT's Fluke again and check it out later tonight, if needed. And this way I can at least see if it's at regular intervals, or at random. It's a small fluctuation and each pair fluctuates together though, that much I have been able to observe.
 
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