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Re: [Amps] SB-220 Output Network

To: Joe <>
Subject: Re: [Amps] SB-220 Output Network
From: Nidhog <>
Date: Thu, 12 Aug 2021 13:28:41 -0400
List-post: <>
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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