i 2007 or thereabouts richard and i acquired a knight 93-SZ0-682 - what that model number signifies is beyond me. it's a cool looking amp and why we were drawn to it. back when richard and i worked on projects such as these, we decided to keep as much of the original ckt as possible. it was nightmare. the common ground bus made the thing unbearable with hum and buzz. we ended up clipping the ground bus for isolation of the preamp ckts and isolating the 1/4" jacks from chassis and viola! a nice clean-ish amp. a few tweaks for gain and it ready for a new home. i ended up basically giving it away for cost of the parts to a friend, mind you, this was ~2008. fast forward 3 years and i get it back - my friend kept hacking at it until it just didn't work worth a $#!t any more. he says to me: "i want clean - loud and clean." i sez ok, and it sat for 6+ years. i tripped over it last september and hut myself. i'm pissed. i was ready to flip it just to get it out my sight, but those words kept haunting me... "loud and clean, pete, loud and clean..." while i was looking at the original schematic, i had just finished listening to a youtube clip of an ampeg portaflex...hmmm. looking at the B15NA schematic, i saw basically the same output lineup and preamp tube type sockets. so, a revelation. this thing is going to be a B15NA with some minor tweaks. the white knob does nothing other than power on/off switch.
1) 6SC7 for 1st and 2nd stages; bonded triodes for a bit more gain; NO bypass caps.
2) sub in a 6SL7 for the floating paraphase inverter.
3) keep it simple as possible: this chassis is the easiest to work in because of the layout and shape - see pics.
4) i used 5881s instead of the 6L6G power bottles and a 5UGB instead of the 5U4G rectifier - see pics for tube lineup - all NOS except the 2 preamp tubes; i reused those.
this thing sounds incredible. very articulate and refined. i now hear why folks love their portaflex. and it's vewy, vewy quiet....
kind of a sloppy on the build; i just wasn't into working in the confines of that chassis any longer than i had to. link to pics below.
https://www.dropbox.com/sh/kemyf59pu9j2i6b/AABv7J2ZGuJM_2SLdsYMYobwa?dl=0--pete
Topic: knight resurrection as an ampeg. (Read 2142 times)