Scott had 1-2 of em from his secret stash. They are a multronics model
90 switch. Rated for 40 amps @ 20 kv. That 40 amps is the 60 hz rating,
not RF rating. They have to be severely de-rated for RF...and as you go
up in freq, the switch assy has to be de-rated even more.
He added a complete set of contacts (including the common) on the back of
the single ceramic wafer. You can only do that stunt on a model 90 switch.
That turns it into an 80 amp switch. It's the exact same model 90 switch
that W8JI used on his 3CX15,000A7 SW AM broadcast HF amp.... and JI also
modified with contacts on both sides of the single wafer. Model 90 is 10
positions, (including common) and 36 deg indexing. To make it a
progressively shorting switch, you order it with what's called a ....' 5
pole rotor'. The 5 x rotors all converge onto the center ...'rotor hub' .
But then you end up with a 6 x position bandswitch. A 4 pole won't work,
(not enough shorts on the coil. IE: when on 10m, rotor #1 always carries
the actual current...and taps the 10m tap on the coil. The remaining 4 x
rotors just short out 15/20/40/80m. (160m always gets a short, since the
far end of 160m coil is bonded to the common..and also the load cap). A 6
pole rotor won't work. Reason is, when on 160m, rotor #6 would be sitting
back on the 10m tap.
Myself I use a triple wafer model 88 switch. Each wafer is rated for 30
amps @ 13 kv. So 90 amps @ 13 kv. I also have a 5 pole sequential rotor on
EACH wafer. Also have...'double commons' for the common contact. (rides on
both sides of the center rotor hub).
2 x buddies used a triple wafer model 85 switch...(YC-156 and a 3CX-6000).
The 85 switch is 12 positions (30 deg indexing)...and each wafer is rated
for 30 amps @ 12 kv. On the model 85 switch, 6 pole sequential rotors are
used (one per wafer). This will provide for 7 x bandswitch positions,
that's it.
All 3 x switches are reasonably priced, new, from multi-tech. (aprx
$350.00). Skip Coleman was the 'go to guy' at multi-tech. He's retired
now. I had bought a pair of new, 2 x wafer, model 88 switches from KM1H.
Skip supplied all the bits to convert switch #1 into a triple wafer
switch. Switch #2 was converted into a single wafer switch, with just a
single rotor. Switch #2 is used to change HV taps on the dahl plate xfmr.
(if only changing between 2 x taps on the sec of a plate xfmr, a SPDT vac
relay works good, provided the default (coil de-energized) is always the
lower V position).
We have all given up on roller coils using tubing for the coils. IF the
roller coil is big enough for 160m, (or even a band switched setup), it
will require at least one extra short with a vac relay, when on 20-10m...or
u will get the dreaded. ..'suck out' every time. The rolling contact is
the weak point. The tubing coil is wound like a thread on a bolt, cocked at
a slight angle. Meanwhile, the pulley that rides on the tubing also has
to be cocked slightly. And to do that, the pulley has a slightly bigger
ID than the inline shaft it rides on..which makes for a semi sloppy fit,
hence a ton of pressure required.
On 160m, temp resistor wired between anode to chassis....to simulate the
plate load Z. Tune and load caps tweaked for 1:1 swr...with analyzer on
output. Then leave caps alone... and sweep the analyzer up / down till u
find the 2:1 swr points, write it down. Then repeat for each band. You
will find that the 2:1 BW on 80m is double what it is on 160m. And double
again on 40m. Double again on 20m. Double again on 10m. Mine was 67 khz
on 160m, 140 khz on 80m, 290 khz on 40m, 600 khz on 20m...and 900 khz on
15m. With the dreaded 'suck out', typ it is fine on 160-30m. However, on
20-10m, the 2:1 swr BW is extremely narrow...that's the instant giveaway.
Note when paralleling the 3 x wafers (or 2-3-4 wafers) on the model 85 +
88 switches, to get the current to divide equally, wafer #3 (wafer closest
to the tank coil), gets the strap to each tap. Meanwhile, the COMMON of
wafer #1 (closest to the front panel) is strapped to the load cap...and
also to the far end of the 160m coil. A single strap bonds all 3 x wafers
together for each band position..and ditto with the common of each wafer.
Done this way, the total physical distance going in on the various taps on
wafer #3 and out on the common of wafer #1 is always identical..and
current divides equally between wafers. IF you instead do the taps on
wafer #3....and bond the common of wafer #3 to the load cap + far end of
160m coil, then what happens is 80% of the current flows through wafer
#3....and only 15% through wafer #2.....and 5% through wafer #1.
Jim VE7RF
On Fri, Jan 12, 2024 at 4:48 PM <donroden@hiwaay.net> wrote:
> Jim,
>
> Where are you getting your band switches ?
>
> Don W4DNR
>
>
>
> On 2024-01-12 6:38 pm, jim.thom jim.thom@telus.net wrote:
>
> 160 Meter Coil Installation, Paralleled Band Switch Contacts etc.
> Here the 10 uh, 160m coil is finally installed.....made from 1/4" tubing.
> Bandswitch contacts have been paralleled. Taps to bandswitch now being
> installed.
>
> https://www.youtube.com/watch?v=ihWAoWn339E
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
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