Interesting journey, it keeps evolving!
Aye, it has certainly changed out of all recognition from the original ideas. At the start I was after power, hence the desire to use KT120s or even KT150s. But that all fell by the wayside and I ended up in a dead end. It took a conscious decision and quite a bit of mental effort to try and actually
design the thing for low distortion rather than merely hope for a low distortion end point. I got there eventually. A couple of Watts of trioded EL34 will do me.
Today I fitted a pair of never-been-used, Russian military, K72-n teflon coupling caps. Simon gave me these, sometime around 2007, but I couldn’t think of anywhere to use them, due to their 0.033uF value.
Because of the very high value grid leak resistors on the El34s, with these low value caps, I was still able to get the LF -3dB point to a reasonable 9Hz ish; higher than the 1Hz ideal yes, but it’s only a two stager and the slightly worse LF phase shift performance is not a problem subjectively. These caps are the icing on the proverbial.
Also the very high grid resistor values (500K in reality, rather than the 470K on the schematic) mean that KT
anything apart from KT77 which below 25W plate dissipation allows 1Meg, is completely out of the question, so fiddling is pretty much prevented.
It’s actually a great amp now. I was up until turned 3am the other day playing records (see the edit time on post 466.) That has only happened twice before, in the last 40 years, so I must have got
something right.
I mean, the thing is, Hi-fi component designers and some reviewers like to talk about realism as their ultimate goal, but that’s not a thing for me. OK, so when playing the 0.1% of very high quality recordings on a super-linear, wide bandwidth, low distortion system, situated within a properly treated listening space, you
might just about be fooled into thinking people are playing music in your room, but I don’t care about that. In the end, all I want is for things to sound good.
Sgt. Baker started talkin’ with a Bullhorn in his hand.