NFB shielding?

[tedmich]

I just picked up a PV Ultra 60 212, a +70lbs beast for very little off C list. The fellow had just had it re-tubed with JJ 12ax7s and Ruby 6L6's and "paid extra to have it biased" (LOL it has no adjustment!)

I opened it up first thing as is my habit, removed a moth nest from the high gain input jack, tightened things down and was amazed at the extra room in this huge chassis (for 2 more 6L6s and the bigger PCB).

I noticed the NFB comes from the OT to the front panel "resonance control" (3rd toggle from right) and that the lines in and out, while shown in the schematic to be shielded, and the having the ground pin present, are only single wires. Its shielded in my Bravo too! And the NFB send and return were all bundled up with the AC lines.


I unbundled them and stuck them down with some 3M Cu tape to the chassis, any ideas on this? It sounds great, very quiet and none of the reverb feedback some others mention in these. I didn't A/B it so it may be spurious, but I am curious as to what other would do.

[Albert Kreuzer]

Can't hurt, although probably not necessary (NFB coming from the OT is very low impedance).
If it sounds good, leave it that way.

Cheers,
Albert

[Gaz]

i thought if it sounded good you were supposed to mess with it 'til it sounded bad so you could make it sound good again

personally, i've never had problems with an isolated unshleided nfb wire. can't speak for one near other sensitive wires though...