Liverpool oscilloscope readings? Any interest?

[Ledvedder5150]

I'm thinking about doing some oscilloscope readings at the output of my Liverpool with and without the PPIMV installed. I feel like, even with the PPIMV dimed (essentially out of circuit) there's still something different. Almost like it's much more gain and compressed than without the PPIMV.

I'm just wondering if there's any interest in actually "seeing" the differences on a scope? Also, if you'd like any readings at other points in the circuit just let me know!

[Ledvedder5150]

Ok, just so I don't forget, these are measures with the PPIMV. Cut control is fully maxed and didn't seem to make much difference in the output anyway. Tone and presence at 12 o'clock, no bright cap. This is a 150mv sine wave into the amp, measured at the 8 ohm output.

PPIMV full, volume 0 -

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PPIMV full, volume 9 o'clock -

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PPIMV full, volume 12:00 -

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PPIMV full, volume maxed -

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PPIMV 0, volume 9:00 -

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PPIMV 12:00, volume 9:00 -

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[Ledvedder5150]

Here are my readings with no PPIMV or cut control installed.

Volume 0 -

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Volume 9:00 -

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Volume 12:00 -

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Volume max -

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[Reeltarded]

hmm.. YIKES

Somewhere catastrophe. Let me go look at guts. The setting at 3 is already beyond fuzzface. Your blocking distortion has bigger shoulders than Atlas.

[Ledvedder5150]

hmm.. YIKES

Somewhere catastrophe. Let me go look at guts. The setting at 3 is already beyond fuzzface. Your blocking distortion has bigger shoulders than Atlas.

Any thoughts where to focus?

[Reeltarded]

Input to PI. Check after each coupler. See the lopsided waveform. Looks like the invertion is angry. (aF!)

Stage one or three is a monkey apocalypse. I am trying to do phase without math but this is my simple theory.

What resistor did you use after stage two?

[Ledvedder5150]

Input to PI. Check after each coupler. See the lopsided waveform. Looks like the invertion is angry. (aF!)

Stage one or three is a monkey apocalypse. I am trying to do phase without math but this is my simple theory.

What resistor did you use after stage two?

68k

[Ledvedder5150]

I'm trying to test the signal with my scope. Is this normal, or would this indicate an issue with a cap or something?

https://youtube.com/shorts/ooGekbg1jI0?feature=share

[Reeltarded]

Not normal.

Turn the amp off and yank the PI to divorce the pre from the output. Generator at input, volume at 0. Check every tone control at the wiper. Check v1b at the coupler output to V2. Turn volume up to about 20% and retest. 50% then retest.

If you don't get any information to help, remover power tubes and install PI. Same test before and after PI couplers. Do these tests on the audio side of the caps.

Look at your earlier post. That sine wave with volume at 0 is already a mess. I am not good enough to know what the problem is but I can easily see what it is doing...

Hey, unsolder the cut control. Let's get the amp back to as near stock as we can.

[Ledvedder5150]

Not normal.

Turn the amp off and yank the PI to divorce the pre from the output. Generator at input, volume at 0. Check every tone control at the wiper. Check v1b at the coupler output to V2. Turn volume up to about 20% and retest. 50% then retest.

If you don't get any information to help, remover power tubes and install PI. Same test before and after PI couplers. Do these tests on the audio side of the caps.

Look at your earlier post. That sine wave with volume at 0 is already a mess. I am not good enough to know what the problem is but I can easily see what it is doing...

Hey, unsolder the cut control. Let's get the amp back to as near stock as we can.

I'll give these things a try today. I do have the cut and ppimv completely removed.

[Ledvedder5150]

This is v1b at the coupler output to v2 with the PI tube pulled. Volume is zero, 9:00, 12:00, and max. I'm not getting much more than a few volts on the tone pot wipers.

20230119_112752.jpg

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[pompeiisneaks]

BTW, I don't know the software on that specific scope but that usb port on the front supports a usb storage stick and you could save those waveforms to files instead of taking photos... gets a bit more detail, but if that's too annoying to figure out, understandable

Most of the scope readings I get for the first few gain stages are in the mV then small volts then mid teens... it's not until like the PI that you get pretty high signal swing, maybe 30-50VAC if I recall? It's been a while though, and every amps going to vary depending on the operating points of different gain stages etc.

~Phil

[Ledvedder5150]

Here's the culprit which was in v1. I swapped it for a different tube and the signal is much cleaner now.

20230119_132258.jpg

[wpaulvogel]

Your third picture in the last waveform post is what’s going to be going into the phase inverter with no master volume and the output will be muddy by that point. The cold biased stage is really for gain control in these amps. The power section is full square wave before any preamp clipping. Because you have added the master volume, the amp will have another character but it won’t be Trainwreck. There’s nothing wrong with it but it’s going to give you a different flavor.

[Ledvedder5150]

Your third picture in the last waveform post is what’s going to be going into the phase inverter with no master volume and the output will be muddy by that point. The cold biased stage is really for gain control in these amps. The power section is full square wave before any preamp clipping. Because you have added the master volume, the amp will have another character but it won’t be Trainwreck. There’s nothing wrong with it but it’s going to give you a different flavor.

That was with no master volume installed. Since I replaced that noisy tube in v1, it sounds great!