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Re: [Amps] SB-220 Output Network

To: Joe <>, Nidhog <>
Subject: Re: [Amps] SB-220 Output Network
From: Mark Bitterlich <>
Date: Thu, 12 Aug 2021 18:15:12 -0400
List-post: <>
You might consider looking at the network design values of the Henry 3k that 
used a pair of 3-500's. Both the 3k and 3k-A ran those tubes with about the 
same plate voltage you mention. They could exceed 2K key down output with a lot 
of drive, but were also were probably into distortion. It's just a thought, but 
why reinvent the wheel?
-------- Original message --------From: Joe <> Date: 8/12/21  1:42 
PM  (GMT-05:00) To: Nidhog <> Cc: Amps group 
<> Subject: Re: [Amps] SB-220 Output Network Thanks,Will 
check it out.It's all working and has worked perfectly without any issues of 
any kind for over 2 years now. No arc's nothing at all. it is just to make it 
have a well you know the load cap is in a good spot you have to run 1400+ 
watts.And want to finally be able not to have to.Joe WB9SBDOn 8/12/2021 12:28 
PM, Nidhog wrote:> You are trying to put a 427 in a Vega.> Go read a handbook 
or go here.> I don’t have a Microslop computer to do the software.> Mouse down 
and do his Pi net design.> Bet there’s others, on the net.> <>>>> Sent from 
my iPad>>> On Aug 12, 2021, at 12:57, Joe <> wrote:>>>> Hopefully 
some of you here may remember my adventures with this SB-220.>>>> I'm the one 
that ran RTTY at full power in a RTTY Contest and >> literally melted down the 
HV transformer.>> And in the process toasted a LOT of other stuff with it.>>>> 
So a complete re-build and change of the HV section was needed.>>>> So after 
looking at what a Pair of 3-500Z's can actually do, I >> decided to try to get 
all I can from them.>> Think like a Big Henry Amp.>>>> I looked at the Eimac 
data sheets. And found a suitable HV transformer.>>>> This amp now has 3800 
volts at rest on the plates and at full load >> 3600 to 3700 volts.>>>> Problem 
is, running this much higher voltage has changed the values >> of the output 
network components needed to be to obtain a match now.>>>> It was discovered 
that on EVERY Band, until the amp is making 1400 >> watts or MORE the load 
control wants to be fully meshed, max amount >> of "C" available.>>>> Once it 
gets above 1400 watts, then you can get a peak on output >> power when 
adjusting it.>> But it is still a very small less "C" like 5% less than maxed 
out.>>>> So a simple thought was add more "C" so added a nice variable in >> 
parallel with the load cap.>> This cap was about 1/2 the value of the main load 
cap, so thought >> this should be plenty.>>>> I was amazed to see that if it 
made any change at all, it was very >> minimal.>>>> So with discussions with 
many on this group and elsewhere, it was >> decided that because of the higher 
voltage, this amp needs more "L".>>>> That is a major re-do for sure so I set 
that on the side. So >> continued to use the amp at 1400 watts or more.>>>> 
Thats been geez 2 years now? The AMP is still running great! But >> often I did 
not need or want to run 1400+ watts, So I bit the bullet >> and decided to try 
to add the More "L">>>> Now I "CAN" just do a poke and not do anything 
Scientifically.>>>> Like on the 10/15 coil, just move the 10 meter tap 1 turn 
longer.>> looking at the 80/40/20, coil, It actually looks like I can add in >> 
the coil form up to 7 or 8 more turns! The grooves in the form are there.>>>> 
Give like 15 meters one more turn,>>>> 20 meters 1 turn>> 40 2 turns>> 80 3 
turns>>>> And just see what happens?>>>> Or is anyone here great with all that 
math stuff that I probably >> learned when I took my extra exam in 1980 or so, 
but have long forgot >> how to do this kind of work to calculate the needed 
components.>>>> But thinking Ok here is a stock SB-220  a pair of 3-500Z's>> 
Stock voltage is what? 2500 & 3000 volts>>>> With stock caps and the pair of 
3-500Z's How much "L" is needed on >> each band.>> I would assume that is how 
much "L" was designed in the Kit.>>>> Now raise the voltage to 3600 to 3800 
volts.>>>> Now how much "L" is needed with the rest still stock?>> for each 
band?>>>> and using the stock 1.75" coil form, how many turns should be the >> 
best chance of working for each band segment?>>>> Anyone willing to try a 
gander at this?>>>> Joe WB9SBD>>>> 
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