50 watter fizz help

[larryb]

I just finished a 1987 50W build that was basically a Weber kit with Heyboers, but their schematic was heavily filtered in the power supply, so I reduced all that. First thing I did after about 5 minutes of fire up was cut the bright cap across the vol pot. It was just way too much.
The amp sounds loud and proud, but I'm getting this odd high-end fizzy, almost phasery thing. Not really badly, but enough to be annoying, as the breakup doesn't really seem smooth with the fizz. It kinda sounds like there are 2 overdrive sounds happening...a beautiful one, and the trailing fizz on top. If I have the volume at lower settings, either on my guitar or on the amp, it doesn't really happen, but when pushed(and this amp starts to breakup early) it's noticeable, unpleasing, and a bit harsh. I'll get some clips up when my neighbor leaves.
I've read about increasing the cap across the plates of the PI to 100p, which I'll try this afternoon, but I wanted to get some opinions on the matter from this board.

Here's some more information on the amp :
~500VDC on the plates(Heyboer is 720V CT)
Running cheap EL34s, that are quite mismatched. With -45V on the grids, tubes are biased to 35ma and 26ma, so I'm at ~70% and ~50% dissipation, respectively. JJ and EH preamp tubes for now
Speakers are Vintage 30 and G12T75
Bright cap snipped
Filtering is 80uf/40/48/48/48. That's just what I had on hand. I want to drop the pre's to 40 eventually.

The same type of fizz thing is happening with my 18W, but worse. Just came across the Ruby zener mod, which I'll try in that amp. nonetheless, any help or thoughts on the matter is appreciated.

[larryb]

Udpate- The HT fuse(.5mA slo) is blowing when I jumper the channels. No issue when I dime one channel but when jumpered and pushed, I get a blue sparks behind the amp and the fuse blows. I'm not sure about the blue fireworks...if thats the actual fuse blowing or something else illuminating. it was not directly where the fuse is, rathjer where the EL 34s are... Put in another fuse and tubes are fine, fires up OK using single channel. This seems unrelated to my fizz issue, but comments about this are appreciated as well.

[Reeltarded]

Change output tubes. One of them is arching and done. The mismatch is causing the fizz too, almost positive.