Here, some updates. This is the beginnings of the elaborate chain drive
assy. 2 x more chains, yet to be installed, plus tensioner's....( for the
vac tune + load caps).
Note on the big model 90 switch, there is a tall, rhombus shaped black end
plate....at both ends of the switch assy....(oriented vertically).
In the normal configuration, the black end plate, at the FRONT of the
switch, is mounted on the INSIDE of the panel (along with the spring detent
/ nylon assy). In normal configuration, only the 1/4" steel shaft sticks
out the front of the panel....through a panel bearing.
In this amplifier, the switch was taken apart, and the FRONT end plate was
mounted on the OUTSIDE of the front (inner) panel....( along with the
spring detent assy).
Done like this so the switch wafer assy doesn't stick as far back on the
inside of the RF deck. There are severe space constraints on the inside of
the RF deck.
Ferrite loaded plate choke finally fabricated...(and tweaked)....and tested
on the VNA. It will be shipped out to Scott later this week. I had to make
new, narrower copper straps ( 1/2" vs 3/4") so I could get an extra 8 turns
onto the assy. The winding is now 5.5" long (vs 5.0") . Final choke config
is now 405 uh. This dropped the 1st series resonance freq down to where I
want it. (1st series resonance now at 17. 125 mhz...midway between top of
20m..and bottom of 15m..so choke won't work on 17m). The amp only works on
160-80-40-20-15m. NO 17/12/10m on this amp. It only has a 5 position
bandswitch...with 4 x sequential rotors.... to make it into a shorting
style bandswitch. And no, we can't re-use the 15M tap on 17m. Reason is,
with the L coil inserted between the plate block cap assy, and the C1 vac
tune cap, it's designed to lower the loaded tank on 15M. In software, if
15m tap re-used on 17m, the loaded tank Q skyrockets to an unacceptable
value. Without the extra '"L" coil installed, the Q is too high on 15M.....
BUT if re-used on 17M, would only increase the tank Q by another 17%. So L
coil installed, low Q on 15m, and no 17m operation. Since no 17m operation,
having the plate choke resonate near the 17m band is a non issue. The model
90 switch is a 10 position, 36 deg switch. The max you can do with that
switch is a 5 pole sequential rotor...which results in a 6 position
bandswitch. Scott is re-using an old model 90 switch, and it only came with
a 4 pole sequential rotor...so only 5 x bands.
Original loaded plate choke with it's 5" winding, was 305 uh, and resonated
at 19.750 mhz....(and also 33 mhz). Interestingly enough, as an experiment,
I removed 3/4" of turns so 12.5 turns were removed...and the winding was
now only 4.25" long. Inductance dropped to 249 uh....and 1st series
resonance shifted up to 23.3 mhz.... ( and 2nd series resonance shifted up
to 39.990 mhz). Ok, winding completely removed....and new, narrower straps
installed. This time, winding length increased to 5.5". Choke is now 405
uh. 1st series resonance is now 17.125 mhz.... ( and 2nd series resonance
is now 29 mhz).
I believe this latest, and last config will work well. It will also
minimize the residual RF current through the choke on 160m.
Stay tuned for more.
https://www.youtube.com/watch?v=exY4_UBmhsI
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