Date: Mon, 16 Apr 2018 08:05:46 -0500
From: Rob Atkinson <ranchorobbo@gmail.com>
To: "amps@contesting.com" <amps@contesting.com>
Subject: Re: [Amps] Alpha 77D anode choke swap?
>50 uh will also work just fine on 80-10m. A buddy uses a 50 uh choke on his
>hb YC-156, which is a 80-10m amp.
<I have doubts about 50 microhenries being adequate for 80 m. Well, it
<might be okay if you used a tremendous amount of bypass capacitance
<but I'd prefer more inductance, less capacitance. A couple
<questions: How much bypass capacitance does your buddy use, and how
<much RF voltage is he willing to subject his power supply to? I'm
<assuming his filter is a bank of electrolytic caps.
<The best way to not have to sweat the h.v. power supply plate choke is
<to use a balanced output network with the choke in series with the
<center of the output network coil where the RF v. is already low.
<73
<Rob
<K5UJ
## You are not after XL. You are after Z..and there is a big difference.
The 50 uh plate choke on the hb YC-156 amp is wound with 20 gauge magnet
wire.
Bypassed at the base with a 4700 pf @ 10 kv disc ceramic capacitor. Also a
1500 pf
@ 15 KV HEC doorknob cap. The 4700 pf cap does a better bypassing job on
the lower freqs.
The 1500 pf doorknob does a better bypassing job on the higher freqs.
## HV filter in the 6700 vdc supply consist of 4 x 47 uf @ 4.5 kv oil
filled caps in series parallel.
That plus a an external box, with 20 x 2000 uf @ 450 vdc lytics in series
for an additional 100 uf. Total
of 150 uf used. I think additional bypass caps were used inside the box
with the string of lytics.
## In any of these 2 piece plate choke setups, like used by creative
electronics, bear-electronics in japan,
my hb versions etc, they typ use a 135 / 180 uh large choke in series with
a 45 –50 uh smaller choke.
2-3 x 4700 pf bypass disc ceramics used at base of large choke. At the
junction of the chokes, the junction
is fed to the hot end of some 500 pf bypass caps. Cold end of the 500 pf
bypass caps is wired to one side of
a spst mech relay. Other side of mech relay contact is bonded to chassis.
3-4 1 meg @ 3 watt series resistors
are wired between cold ends of 500 pf bypass caps..and chassis. The
resistors ensure the cold end of the 500 pf
bypass caps are DC grounded, so the 500 pf caps are in B+ blocking mode.
The larger choke is typ would with 22 gauge
magnet wire. The smaller choke is typ wound with 18 gauge magnet wire.
## with relay de-energized, both chokes are effectively in series... and
used on 160m only. On 80-10m, relay is
operated and cold ends of the 500 pf caps are now RF grounded. This
effectively switches out the larger 135/180 uh choke.
IF both chokes are used on 80m band, you end up with extreme high voltage at
the junction point, and all hell breaks loose.
Ditto if both chokes used on 40m band. After seeing the flame thrower show,
then I understood why the commercial makers
used the smaller choke on 80-10m.
## If you check W8JIs notes, where he uses an analyzer on his Ameritron
choke, you will see that the Z is sky high on several bands,
esp 40M. RF current is just a few microamps flowing through the choke on
40m... and only slightly more on 80m.
Worse case for that choke is 160m..and also 10M.
## Get close to a series resonance point..and Z drops like a rock. The
B+W 800 choke is 90 uh, but typ resonates either at the top
end of 15M band, or slightly above. The fix for that..back in the day was to
remove 4 turns from the top of the choke, to move the resonance
point up a bit, but back then we did not have a 12M band. EG: XL = 2 X
PI X FL. 90 uh = 11,869 ohms of XL on 21.0 mhz.
Well the 11.869 K ohm of XL does not do any good, when the Z is through the
floor, cause the 90 uh choke just happens to resonate on 15M band.
## A good plate choke will exhibit a Z of at least 500 k ohms..and higher,
this is what you want.
## You also have to factor in the DC plate current flowing through the plate
choke. I tested several hb chokes in the shop, using my 0-60 vdc @ 5A
current limited lab supply. The 27 gauge magnet wire used on the 180 uh
large choke, like used in the henry 8 K ultra, was fine up to aprx 1.3 amps.
Above that, it would go into thermal runaway..and fast, and run extremely hot.
With 22 gauge, I could run 5 A CCS for 30 mins and zero temp rise.
## On another buddys YU-148 amp, it too used the 2 piece plate choke setup,
with the smaller 45 uh choke mounted at right angles at the top of
the larger 180 uh choke. We still had problems with extreme HV at the
junction point, even using a vac relay between cold end of 500 pf caps..and
chassis.
The concept was the 500 pf caps at the junction point would dc block the 8kv
B+.... so any junk box spst mech relay could be used to ground the the cold
ends
to the chassis. The fix was the inclusion of the 3-4 megohms between cold
end of 500 pf caps...and chassis. Only then is the 500 pf caps really in B+
blocking mode.
We found that out in the alpha 87A manual, etc. They used 3 x resistors in
series to DC ground the cold ends of the junction caps. These days, alpha
uses the same gapped choke
as what you see in the ameritron chokes..and also sold by RF parts. All 3 x
chokes are identical. So no more 2 x piece choke + relay + resistors.
## The ameriton / rf parts choke is superb, but its wound with puny 28
gauge wire, so has its limitations, esp if high plate currents are used... and
/ or higher B+ voltages
are used. The higher the B+ voltage, the higher the RF voltage is on the
choke..which will result in higher RF current through the choke.
## On a side note, while having all the problems with the YU-148 choke setup,
the 45 uh smaller choke was used by itself for a few days. The 45 uh choke
worked just
fine on 160M, albeit, a lot more tune C was required. The B+ supply for
the YU-148 amp used 24 x 3900 uf lytics in series. The Z was still high
on 160M..even with just
45 uh. The 180 uh large choke was reduced to just 135 uh.... with the same
flame thrower show going on. Later on, with the resistors added, all was well,
provided both chokes only used
on 160m. Since the YU-148 amp only covers 160-15m, I decided to increase the
value of the smaller choke from 45 uh... up to 70 uh. The 18 gauge magnet
wire was removed from the
small 45 uh choke..and replaced with 22 gauge wire. With the smaller gauge
wire, more turns on the same teflon form resulted, so the uh was increased
from 45 up to 70 uh. And that
was using the same form as b4. We could have gone even higher, but time
constraints didnt allow for a lot of experimentation. 70 uh resonates well
above the 15M band....and 70 uh works
just fine on 80-15M. 135 + 70 = 205 uh..which is what is currently being
used on 160M. 180+ 70 = 250 uh, which will also work good on 160M.
## The CERAMITE brand of disc ceramics in the 4700 pf size, are available
in both 10 kv..and also 15 kv size. Sold by both mouser...and henry radio.
In the henry 8k ultra, they used
a 180 uh + 20 uh setup...with the larger choke being completely shorted out
end to end on the higher bands. At the base of the large choke, 3 x 4700 pf,
10 kv disc ceramic caps used...and also
3 x 500 pf, 15 kv HEC doorknobs. The last production runs of 8K ultra
used an entirely different plate choke setup. The last production 8K ultras
also did not use the 1 turn chrome parasitic
suppressor. No suppressor was used at all in the last production runs. The
secret is to NOT feed B+ though any parasitic winding. The plate choke setup
sits off to one side of the tube..and any
parasitic suppressor sits off to the other side of the tube. If no suppressor
used, the RF still exits the tube well away from the plate choke to anode
connection.
Jim VE7RF
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