[Bret Ludwig[_2_]]

The Marantz OPT takes most of its LF NFB from the 4 ohm tap on the
sec. But there is an additional NFB winding with its live end connectd
to the 16 ohm tap via 10 ohms, and the NFB winding feeds HF NFB to the
V1 cathode via 1.2nF. I'd guess the NFB winding does not experience
the same phase shift caused by LL and the load at HF, so Marantz
manages to apply NFB over a wide BW without trying to fix the phase
lag at HF. But without having a Marantz here to examine, I cannot say
exactly how well the arrangement works, or understand exactly how
Marantz wound its OPTs. How can I endorse something I have never
examined properly? Impossible. But if Marantz had used a 5P x 4S
interleaving pattern with 6 secondary sections each for 16, 8 &4 ohms
and all paralleled, there would have been no need for a NFB winding
because such interleaving with paralleled secs give wide BW for this
sort of amplifier as Williamson and McIntosh have so so clearly
established over the last 60 years. Tapped secondaries usually have
higher winding resistance than *where 4 sec sections are strapped in
different patterns for the load match variations.

That's called "British Secondaries". Americans went with the 16/8/4
arrangement because that was more convenient for the USER. The
Mercury Magnetics VTO100 in the old VTLs uses this as well. I think a
lot of Partridges and the Radford used this as well. My guess is the
VTO100 is a Radford copy.


Most manufactuers
have used appallingly thin wire in OPT secs and rarely ever have 4 Sec
sections; two if you are lucky, and often the two will each be a match
for 4 ohms, so that the two series S sections give 16 ohms, a tap
along one section gives 8 ohms, and only one section is then used for
the 4 ohm match and it is with 4 ohms that there is the highest LL and
worst BW and highest instability and highest winding losses. As i
said, for good performance for a 50W OPT, you'll need 5P x 4S, and
each Sec section should be a match for 16 and so with 4 ohms you still
have 5P x 4S interleaving, even though 1/2 the sec turns are unused.
The strapped method of changing Z match on OPTs is often done poorly.
For example, in Quad-II there are only two link changes needed for 8
or 16 ohms, but no official match for 4 ohms. Walker must have
pondered how to set up the OPT and its strapping method long and hard
to satisfy a Nation Full of Dumbos who are confused if forced to count
beyond 3. Quad-II would be a MUCH better amp if it were possible to
strap *all OPT secs to get a wasteless arrangement of secs so that
every length of secondary wire had the same current density.
Then the Quad-II would have allowed a P-S load match of 4k0 : 4 ohms
which would better suit most modern LS, and of course using 8 ohms on
the 4 ohm outlet gives 8k0 : 8 ohms and nearly all class A which suits
the old junk circuit best. See why I say old junk is OLD JUNK?
Its because I can see that the old gizas who designed all that old
junk *could* have made masterpeices with an extra 2 hour's thought and
4 hour's more labour. *But alas, the designers were addicted to
mediocrity.

Well Patrick, you are just so much smarter than those old
guys.......No one did that then because it was not necessary.

You are a crank, is the bottom line.