Hi folks, I've built an amp similar to the Ampeg B15, but with a KT88 output stage. Sounds nice, but I was anticipating more clean wattage. It starts clipping before reaching 50W, and peaks around 75W squarewave if I raise the input signal slow enough.
Output transformer is the 5K/100W Hammond 1650R. Power supply is 525V plates, separate screen supply at 360V. Biased at 60%.)
The output signal compresses a lot on transients. Plenty of voltage swing from the PI, with the KT88s removed the signals are big and clear. Thinking it might be a loading issue with the 100K grid leaks I tacked in some source followers a la Mosfet follies (with +/-150V supply) to no avail. In fact, this lost a few watts of headroom.
Just wondering if anyone could suggest a next step, I was hoping for 70W clean perhaps that was naive or perhaps I've overlooked something?
Attached is a schematic. Thank you!
Output transformer is the 5K/100W Hammond 1650R. Power supply is 525V plates, separate screen supply at 360V. Biased at 60%.)
The output signal compresses a lot on transients. Plenty of voltage swing from the PI, with the KT88s removed the signals are big and clear. Thinking it might be a loading issue with the 100K grid leaks I tacked in some source followers a la Mosfet follies (with +/-150V supply) to no avail. In fact, this lost a few watts of headroom.
Just wondering if anyone could suggest a next step, I was hoping for 70W clean perhaps that was naive or perhaps I've overlooked something?
Attached is a schematic. Thank you!
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