I have a PDF op/service manual for the 2701C which Valhalla gave to me a few years back. It mentions the -LNF option but gives no circuit details. PM me if you can use it.
The manual I have , and have attached here, also mentions this option but has no further detail either . What I find odd is that Valhalla themselves say they don't have the details.
Or some one couldn't be bothered hunting through a filing cabinet
I'm beginning to think that the -LNF variants were hand adjusted, potentially by a very small number of people (1?); and those people/person isn't with them anymore, so the information is lost. Honestly, the only differences I see, other than removing a lot of the HV path is 7 capacitors. 4 across each of the pairs of terminals, and 3 in parallel with R42A/R42B/R41 -- 0.1uF 5% 100V caps that might be custom rolled (yellow, paper? unsure, can't take a picture at the moment).
Valhalla told me to check the output voltages and all of the rails match the schematic, except the HV rail between I and J on sheet 1 of the schematics.... that one simply isn't specified. I'm getting 376V potential across I/J which appears to simply match TR201's output between E20 and E21 (280V) plus TR202's E9-E10 (93V). I asked them to confirm what voltage should exist there and was told that they don't know --- they don't have an LNF to check.
As an aside, on sheet 1, TR6, part of the output drive, is listed as a TIP29A in the parts list; is a TIP31A a reasonable substitute there? I *THINK* it is based on the specs of each... but the TIP29A I pulled from the board seems to be fine according to this peak atlas DCA75.
I sat down with a "real" EE and the schematics a couple of days ago to look at the output drive section and at this point I'm wondering if the zener, D3, isn't misbehaving. In circuit, it is ~1.5MOhm in 1 direction, and ~55kOhm in the other... but in circuit could be lying to me.
Incidentally, I sent the same pictures from earlier in this thread to Valhalla asking if they could verify if that is what an LNF was supposed to look like, or if it was someone else's butcher job... They didn't appear to know, at least, they didn't answer that question, which was the only real question in my email.
Eventually this thing will work again....
-j