I don't see a manual online for this variant of the ots. There are 2 trimmers in the layout - the FET one and the phase inverter one. The FET one you set to taste I think - start out with it in the middle. The Phase inverter one is set with a DMM once you have everything else running, and it isn't critical where it is when you power up the thing, so set it in the middle for now. Email Nik for specific instructions about how to set the phase inverter for this amp, although I suspect it's pretty much the same as the other amps - look at the standard ots manuals.

Thanks Sduck and boldaslove6789
very informative, wish I had an Oscilloscope and a weathergirl now LOL.
Since I do not have either I will probably just set it to 12:00 and then tweak it gradually by ear.
I did ask Nik this same question, his response was much shorter than the amp garage. But he didn't include pics of his weathergirl!

just set it to the middle.

This one, you wont kill anything, really even if set to extremes.

Then adjust it so that it's slightly off than each other, or to your liking.

Thanks again
Todd

I've been reading the same PI balancing thread as you Hywell.

I had originally fitted a 'balanced' tube from Watford Valves, think it was one of their standard Harma (JJ) type.

I changed it last week to a Harma Retro ECC83, not specified as balanced and I have to say that I noticed the difference and prefer this new valve without doing any more PI adjustment - my pot is pretty much at the midpoint.

I have read that some rave about the Long plate Sovtek in the PI position so I've bought one of those to try as well, again the non balanced version.

I found this post on that thread at Ampgarage which seems to sum it up in very non technical way.

I think starting with a matched/balanced tube is probably the best place to begin. Atleast I hoping cuz I just received my tubes today, which I spent extra 5 bucks to get a balanced one.

Got all Tung Sol 12AX7's and TAD 6L6WGC-STR I hope they sound good!!

When you say "shoty" do you mean microphonics or something else? I normally use JJ's in my other amps, but it seems they are not as popular with the dumble clones. we'll see, I guess.

 Sorry what I mean is that a lot of them I've tried have malfunctioned or simply didn't work (even when I bought them from a place that tested them). I had to pick through a bunch to get one that  sounded decent & wasn't microfonic. When I got that good one it sounded great but it isn't worth the hassle. I then switched to the Mullard reissue ECC83's which are consistent and sound great in just about all position's even in the PI. I've been using them ever since.

Before posting on that ampgarage thread and exposing my utter ignorance I thought I post here and see if I am even in the right ball park. Any help apreciated.

I set up to generate a 440Hz signal from (yes I know) a file played on my mobile phone (mylaptop wouldn't do signal out and in concurrently, I need my external sound module back from my son!) in at FX loop return. Presence to 0.  Speaker out to my Hotplate set to load and the line out of the Hotplate to my laptop running that software I mentioned in an earlier thread. Line level set to minimise distortion.  This gives me a nice spectrum analysis of the amp output. I am able to capture the spectrum and save it. So far so good.

So I got this Sovtek LPS, supposedly balanced. DC across pins 1 and 6 measures from 4.5 to -2.3. When I measure AC i get 3.1volts. The trimmer makes no effect on the AC balance, however the trimmer does make a difference to the waveform, the second harmonic being minimised at 4.5 volts DC( trimmer full anticlock)

Next I try a Harma, DC 21.7 to 14.5. AC nearly in balance at 0.3volts. Second harmonic the smallest of all the valves I test.

Various other JJ tubes give quite varying results but no nearer than 2.2 vAC. In all cases the second harmonic is lowest at trimmer set fully anticlockwise. I now wonder whether I need to change one of the resistors?

So I try by ear and it does seem the HArma has something the Sovtek doesn't but its minimal and I now am beginning to suspect I'm chasing shadows and I too am wishing I hadn't read the ampgarage thread. 

I suspect the Sovtek and now need to ask more questions at Hotrox about what they mean by balanced. It seems transconductance balance is whats required here but I'm not sure thats what I got. The Harma seems to be getting closer to AC balance but the voltages are way different from what I was lead to believe was correct (Nik says 6vDC, others 6-10) I also check the two 3.3k grid resistors and find 3.66 on V4 and 3.46 on V5. Way off spec, by 10% and 4% so I wonder if I need to change those at least to get them to match?

Where to go next? Any guidance  welcome, including 'stop bothering', and 'you're out of your depth' or 'take it to a tech'