[Amps] Alpha 77D anode choke swap?
jim.thom at telus.net
Sat Apr 28 15:17:52 EDT 2018
Date: Tue, 24 Apr 2018 12:32:47 -0500
From: Rob Atkinson <ranchorobbo at gmail.com>
To: "amps at contesting.com" <amps at contesting.com>
Subject: [Amps] Alpha 77D anode choke swap?
## You are not after XL. You are after Z..and there is a big difference.
No pure resistive component to the imaginary number. Anything else?
## The 50 uh plate choke on the hb YC-156 amp is wound with 20 gauge magnet
It can handle more current. That doesn't reduce RF voltage to the
## Bypassed at the base with a 4700 pf @ 10 kv disc ceramic capacitor. Also a
@ 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.
If they are paralleled you have 6200 pF. I don't have time to do the
math but I would still want more inductance. That much capacitance
might be okay for a linear RF amplifier though.
I find your comment about the disc caps being "better," curious. With
ceramic capacitors, "better" relative to frequency usually means lower
frequency current rating, and higher current rating means lower or no
value drift. Disc ceramics don't usually do well on lower
frequencies, especially 160 m. It makes much more sense, if you need
6200 pF to get that job done with one or more doorknobs rated for a
few amps at 1000 kc.
## HV filter in the 6700 vdc supply consist of 4 x 47 uf @ 4.5 kv oil
filled caps in series parallel.
That's all you need. Get rid of the electrolytics. Too much filter
capacitance and stored energy. Oil much more reliable.
<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.
### easiest way to end this argument is to actually measure the RF current at the base of the plate choke,
using a clamp on RF ammeter...and also repeat the test on each band the choke is being used on.
A safer method would be to measure with the clamp on RF ammeter, at
the cold end of each bypass cap in question. IE: between chassis and cold end of bypass cap.
## These ceramite brand 4700 pf at 15 kv disc ceramics are huge things. 1.125 inches in diameter,
and exactly .375 inch thick. The 10 kv version is slightly smaller diameter, and slightly thinner. Trust me, they
will handle one helluva lot of RF on the lower freqs, like 160M band. Typ 2-3 are used at the base of the plate choke
of any choke thats used on 160M. Typ 2 used on any choke whose lowest freq used is 80M.
## Even a plane jane .01 uf @ 1 kv disc will handle 1 A or more on 80m. A .01 uf @ 2 kv disc ceramic handles
a lot more RF on 80m than I thought it would. .047 uf = 4700 pf. .01 uf = 10,000 pf
## The biggest value HEC 15 kv door knob is a HH-57... and its 1500 pf. Rated for 5.3 A CCS.... from 100 khz to 100 mhz.
I have 6 of em packed away. I also install some bypass caps right inside the HV supply itself.
## Those CD brand 47 uf @ 4.5 kv oil caps are 10 inches tall, 8 inches wide, and 4 inches thick. Steel cased, and weigh exactly
30 lbs each. 120 lbs + crate is a lot of weight to have shipped. They also have to isolated from each other..and chassis, when used
in the series – parallel config. One big .25 thick sheet of red micarta under all 4 of em. Then .125 thick sheet of micarta between
each oil cap. Those caps originally came from Henry radio, back in the mid 70s. I sold the completed HV supply to a buddy,
to use with his YC-156 amp. IMO, oil caps are too heavy for the amount of C you get out of them.
## No such thing as too much filter capacitance and or stored energy. As long as a HV fuse + 50 ohm glitch used, I can
cro - bar these B+ supplies all day long, been there, done that. XXX Vdc / 50 ohms = the same value of fault current, regardless
of how much C used. 3-8 kv will kill you anyway, regardless of total C used. Heck, the plate xfmr by itself, with no diode board or
HV filter will also kill you. They only use 2200 vac for the electric chair. Just use common sense, interlocks, multiple HV meters, etc,
and its all safe.
## I have experimented with various values of filter C. Aside from ripple being directly proportional to filter C being used, the dynamic
regulation when more filter C is used is astounding. It barely wiggles if that. Loads of filter C also works really good on any doubler setup ,
since the caps only get charged up every 16.6 msecs... instead of the usual 8.3 msecs.
## On these bigger HV supplies, we run into a one off unique problem. The V drop from the street is like 6-10 vac. My 200 amp
service consists of 3-000 Cu from 200 A panel to meter, and more 3-000 CU from meter to pot head. Then its spliced into 1-0 AL..
for the drop wires from the street. My drop wire terminates on a mid span..across the street, then it travels way down the street, 2 x
poles down, till it gets to the 50 kva xfmr. All the wire out on the street between poles is also Al. AL only conducts 60% as good as
Cu, then having a drop wire thats 2 x gauges smaller doesnt help regulation. So 9 homes hanging off the same 50 kva xfmr.
## That 6-10 vac sag really mucks things up..esp on a 7-8 kv no load supply. Then toss in the V drop across the 50 ohm glitch R, and
then the normal drop you get on any HV supply... and I’m not impressed. My solution was to try to compensate with loads more filter C.
## Latest experiment uses 24 x 10,000 uf @ 450 vdc lytics in series. 417 uf in total. I also have another 24 x 10,000 uf caps for
a 2nd bank. Both banks can be strapped in parallel if required. Caps were dirt cheap surplus. 3 inches diameter x 9 inches tall.
.007 ohm ESR per cap. 253 lb Dahl xfmr used. Ok, now I end up with my version of a regulated HV supply, doesnt budge.
## who the heck is gonna used a balanced network on the output of a tube amp ? However I have seen it done on a HF SW
broadcast TX....which used 2 x tubes .
### Getting a plate choke to work is not too tricky. I may well try the VE3s trick of using 2 x chokes, big and small, with cold
ends bonded together, then toggle between the top ends. SPDT vac relay wired between anode and top of each choke. Then
you can easily optimize the 2 x chokes. Like say 300 uh for lower bands.... and perhaps 50 uh for 20-10m.
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