Always good to read your comments John.
Many moons ago I worked for a company making 100-250KV supplies for
industrial use such as permanent pressed clothes. The PS was basically a
many, many stage multiplier right off the AC line.
Id love to find iron rated at 1000-1500W audio, they seem to be gobbled up
by speculators and opportunists who scrap the BC rigs and get top dollar on
Ebay, etc. I wound up with a beast rated at 7400W audio for cheap that sits
on the basement floor and I built the PP 304TL deck and PS on top of it. Its
still in the oil and weighs 385#, a simple task for my 2T cherry picker and
lawn tractor to remove from the pickup bed and lower down the bulkhead
stairs.
The 115V primary, 6000/7500 VAC CT @ 1.5ACCS iron got in the same way, thats
around 275# and came from a defunct shoe manufacturer. Thats fed from the
main breaker at 240V into a 240/440V 5 KVA step up, across the basement thru
#8's into an identical xfmr and then into a 28A 240V variac which drops it
down to the range needed for the tubes. Voltage drop under load is nil with
a pair of 250TH's running bright orange on voice peaks and the 304TL
modulator. The big xfmr was Free and the other pair were around $20-25 some
years ago that took up room until I found a use for them.
I also run 10KVA iron at 240/660V to feed up to 250' to outbuildings where
there are welders, compressors, machinery, etc. I think I got all 3 for
$100.
Carl
KM1H
----- Original Message -----
From: "John Lyles" <jtml@losalamos.com>
To: <amps@contesting.com>
Sent: Friday, March 26, 2010 12:41 PM
Subject: [Amps] building your own amplifier again
> VE7RF makes a pretty strong argument towards using bigger tubes like
> YU156, instead of trying to squeeze a kW or 2 out of an 8877 or pair of
> glass triodes. I think he is on to something as far as dollars per watt
> goes. I prefer the Almost All Digital LCR meter, and have been going to
> SK widow's yard/sales around here for years, to accumulate a decent
> stash of iron. Just keep in touch with the local hams and you'll find
> 'em. Also, EPAY does come up with decent iron every few months, if you
> don't mind paying twice (for the item and for shipping it). I've gotten
> quite a bit of audio iron this way, for AM projects and ideas.
>
> Broadcast stations are one my best sources of HV power and inductive RF
> components for HF projects. Many have dumped or are in progress of
> dumping their tube 1 kW rigs, AM and FM stations, so these usually have
> something around 2500-3500 volts at just under an amp. And most are
> tapped on the primary to give a range of voltages. And the best part is
> that they were designed for class B or H, with 24/7 operation for years,
> made by decent manufacturers like Basler, SNC, Electro/Stangenees, NWL,
> Magtran and others. You can find them on ebay (take the whole
> transmitter and gut it) or by meeting with the local station engineers.
>
> One opinion that Jim and I differ on is the amount of capacitance for
> filtering the HV, and that is basically a difference in design
> philosophy, which has been beat to death the past week here. I build
> pulsed RF amplifiers for a living, so high stored energy is a norm, when
> you need 200 amps of plate current 10% of the time. But it really sucks:
> the protection circuitry, always wondering if this will be the big bang
> moment at turn on, 20 page safety procedures on shorting out the caps,
> and annual training for all the technicians and engineers for the thing.
> I can tolerate a little power droop or ripple, if I can get away with
> it, in a continuous carrier RF system (or modulated). I have already
> stated that having three phase primary power is quite a wonderful thing
> for power supples. There is no concrete rule, to each his own on how far
> one carries things. If you are making something commercial, then there
> are overlying rules that the corporation will have that limit the amount
> of over-design that an be tolerated, cost and time wise.
>
> Carl's suggestion about thinking out of the box and looking a
> line-operated doublers is another way. Be sure to breaker or fuse the
> line properly so that if you get fireworks you don't cause a fire, since
> you don't have the impedance of a transformer in there anymore. At work,
> we have two VERY LARGE 750 kilovolt DC power supplies, that power the
> proton injectors for accelerator. They are just large room-sized voltage
> multipliers. We have a ~8 KHz audio power amplifier (pair of something
> like 3CX20,000's push pull) feeding a Haefly oil-filled output
> transformer about 4 feet tall. This outputs about 50,000 volts of audio,
> which then feeds the multiplier stack. You may have seen it on Nova or
> Bill Nye the Science Guy, seriously, they filmed it in the 1990s - big
> science...that thing won't supply amperes, but will do milliamperes.
>
> If you started with a 220/440 step down transformer (very common at junk
> houses, building tear downs, and electrical suppliers) run backwards,
> and then have a big multiplier stack with diodes, capacitors and
> resistors, you got some plate voltage with plenty of current. And it is
> isolated from the line in this case.
>
> My pole pig is 10 KVA, 13.8 kV to 220. It is destined for a big tesla
> coil, spark excited, when I retire. It is frothing with PCB oil! It does
> take a tractor with loader to move such things (Kubota 22 hp in my case).
>
> Start building amplifiers again, darn it! I hate seeing this craft
> fading away with (us) old timers. There will always be a need for high
> power RF to cut the mustard at some point. Hams were pioneers in this
> art, and its sad to see people snapping up $5000-10,000 amplifiers
> instead of whipping up something a little ugly in the basement with $500
> worth of materials or less. Despite what we infer here, it ain't rocket
> science at all! They are certainly a lot easier to design and build than
> receivers and even exciters.
>
> One caveat for me, has been finding time to build things at home
> anymore, but thats another story. And having time to use radios.
>
> 73
> K5PRO
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