Thanks for the lead!
Now can anyone scan those page(s) and e mail them to me?
I do not have access to any of the Handbooks. I had the CD version, but
can not seem to find it.
Joe WB9SBD
On 10/11/2021 10:26 AM, gudguyham wrote:
As far as Q, most ARRL handbooks have charts based on plate impedance
and show C1 L C2 values for a Q of around 10-12. Look at the chart
that fits your plate impedance. Set C1 and C2 to the values on the
bands and adjust L for maximum output or a peak in output at those
settings. When you find the peak for L that is where you want L to
be. Then tweak C1 and C2 for maximum output, they should only need a
small tweak. Note the L setting. Your Q will be very close to 10-12
that way. Q is not overly important unless it’s totally out of the
realm of reality. Too many stress out about this. Most amps believe
it or not take whatever Q they can get on the lowest and highest band
and leave it at that. Some amps suck big time on the high and low
ends. The best 3-500 amp I’ve seen with very good low and high band
operation is the Kenwood 922. Worst I’ve seen is Ten Tec Centurian.
The 922 is miles ahead of anything in its class.
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On Monday, October 11, 2021, 10:34 AM, Joe <nss@mwt.net> wrote:
This IS a valid question.
I am not sure about others, In my case it was 90% Cost. With side
effect
benefits.
I knew that for high duty cycle modes you should run this amp at
reduced
power.
I was using the SB-220 at 500 watts output in a RTTY contest. But I
guess even that low was not low enough for about 4 hours into the
contest the magic smoke that makes this stuff work escaped from
the HV
transformer.
Shopping around for a replacement transformer gave me a major case of
sticker shock. I bet the cost of all the replacements I was
finding was
close to the cost of the AMP when it was bought new! I was ready to
either shelf the amp or sell it.
Then thought, well voltage is voltage, is there anything else out
there
that can make the same or similar voltages and would work.
And there is, Yes it is considerably larger than the original
transformer, so it required some modifications of the chassis of
the amp
to allow it to fit. But it does fit. Barely!
And it cost 25% of what all the replacement transformers were wanting.
And yes with the raised voltage and the cost savings I decided to
make
changes to the whole HV section too. Changed to safely handle the new
parameters. Whole new caps and resistors, New Harbach HV board
etc. I do
not know if it is the new cap bank, or the transformer itself, but
it is
incredibly stiff compared to the stock one that was in there. The HV
voltage drop from no load to max out is not even 100 volts! like
3700 no
load to 3600 at 2Kw.
The AMP runs stone cold, it is HARD I mean HARD to get the plates to
even turn red, never mind the orange that people say it should
often do
to "Getter". At 1500 Watts OUT, Even with it transmitting a dead
carrier, after minutes of making RF, the plates were still gray.
At 2Kw+
out, during a normal like Sweepstakes exchange of length, you may get
some Red plates. Orange needs the same 2Kw AT A SOLID CARRIER for
about
a solid minute to get to the orange state.
Yes the output network needs work. Unless I run 1400+ watts all the
time. Then the network runs fine!
I have learned that I need more "L"
But that is a work in progress.
Trying to find good new taps was a pain. So in the amp now is a 18uH
roller inductor.
So now the only thing the output bandswitch is now doing is add
that cap
when on 80 meters.
Now I am still lost when it comes to this "Q" thing.
And what are the optimal settings for this network. That roller
changes
everything.
I can get a perfect 1 to 1 match, with the Plate cap at absolute
minimum
meshed state, and I also can get a perfect match, with the cap
like 50%
meshed, like where it would be normally on 40 meters, but still on
ten.
By the roller being in a different place. And of course anywhere
in-between.
I am learning this combo of different values of plate cap and the
inductor, is what determines the level of that mysterious "Q" but
then
again I may be wrong here.
The AMP is like 99% ready to be put into service,. Just need the help
with this "Q" Stuff, and to discover what to do with the plate cap
and
"L" values for optimal performance.
Joe WB9SBD
On 10/11/2021 4:49 AM, Rob Atkinson wrote:
> Why do some of you guys want to jack up the plate v. on your 3-500s?
> The power difference won't be noticed and you'll create a cascade of
> problems. You still have the same plate dissipation and plate
current
> limits. The pi network won't work, the DC blocking caps may become
> marginal, the power supply filter cap bank may get stressed and the
> IMD spec. gets worse. If you want to jack up the B+ get a 3-1000Z.
>
> 73
>
> Rob
> K5UJ
> _______________________________________________
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> Amps@contesting.com <mailto:Amps@contesting.com>
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>
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