Always get me down ...
(in the workshop)
And ... ladies and germs, for your edification and pleasure tonite ... I bring you ...
(drumroll please)
The obligatory first glow shot ...
That's my "backup" set - a Chinese rectifier, RCA clear tops, and a set of Psvane HiFi KT88's. I figure to hold off a bit on the KT120's, my special set of drivers, and a high end rectifier until I'm sure the amp is right.
Everything biased stable at 55mv, and got sound. Left it running full power into dummy loads for about an hour and transformers weren't heating at all. Wahoo!
Couple fiddlybits to take care of ...
- I got the volume pots bass ackwards. Simple wire swap end to end should take care of that.
- Ditto on the bias pots on the right bank. Same fix.
The panel meters are WAY off ... with 55mv on two different VOMs, those are showing 70. Have to dig into those and see what I got for adjustment. No biggie - even if I can't get them adjusted properly, they're consistent, so I can just remember the error level. Still glad I also included the test taps. Oh, yeah ... two of the test taps are mighty tight, so I'll ream those out a bit when I dig into the rest.
I do have an issue with the input wiring. Had a helluva hummmm in the left channel when I first powered up. Played around with the easy stuff first, and found that I could get good sound out of both channels by holding the center pin of the RCA cable to the outer jacket of the socket. So, once again ... should be a simple wire swap. I expect the reversed wiring on the volume pots have something to do with it. Good news is there's no hum and I get a clean signal when I fudge the connectors, so the long runs to the back of the box should work fine.
Having taken some ... er ... uh ... "liberties" with the original design, I'm surprised that's all that's wrong. My biggest concern was the PT network, but both sides are working, and I do get the expected watt drop in triode mode.
PS ... even when I figured out the input issue, the left channel was still tinny. Huh? Come to find out the el cheepo speaker I got tacked up into the rafters had fallen out of the case. dOH! A bit of duck tape took care of that. Would all life's problems be so simple.
Done for now ... I'll dig in tomorrow and take care of the short list. Can't wait to see what it sounds like on REAL speakers ...