Fender BF Bassman AB165 output waveform issue...

[pecorporation]

https://youtu.be/ZdhbviuSCvU

Hi folks and thanks in advance for any input,

Have a Bassman head here with all new tubes, all new caps and all contacts cleaned, that has an issue. The attached video is the amp at full volume with a KHz input wave with an 8 ohm output load and as you can see, the top and bottom of the waveform fluctuates. Any ideas?

Here's some pics of the cap job...

[Leo_Gnardo]

I see the vid is filed in "comedy" category.

Nothing to worry about, as you get to max output, you can see the wave modulated by the charging power supply. Totally normal. Go past clipping & you'll see more of it. For fun waveforms, pick a test frequency that's nearly a multiple of your line frequency, say 118 or 121 or 183 Hz, then the wave kinda 'swims' around & does the boojie woojie. Very entertaining.

[pecorporation]

Thanks for the quick reply, Leo. I forgot to mention in the post that it does it at any volume setting and at any frequency.

[Justin Thomas]

And, how's it sound with a guitar plugged in, with a 4-ohm speaker load, at full output?

Justin

[pecorporation]

Justin, it sounds great. Nice and quiet, no hum and crystal clear. Just never saw that in a waveform before.

[Enzo]

And did you replace the bias supply filter cap too?

[pecorporation]

Absolutely, Enzo. All electrolytics have been replaced.

[rf7]

I just re-capped one yesterday and it exhibits the same issue. I thought maybe I had a bad cap, but I paralled a new cap on each filter cap (one at a time) and it did not make a difference. I understand it happening when the amp is clipping, but it happens at lower levels too, which I don't expect.