[Amps] SB-220 Output Network

[Joe]

I looked at their schematic. and it's totally different.

Joe WB9SBD

On 8/12/2021 5:15 PM, Mark Bitterlich wrote:
> 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 <nss at mwt.net>
> Date: 8/12/21 1:42 PM (GMT-05:00)
> To: Nidhog <robrk at nidhog.net>
> Cc: Amps group <amps at contesting.com>
> 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 WB9SBD
>
> On 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.
> > http://www.ifwtech.co.uk/g3sek/ <http://www.ifwtech.co.uk/g3sek/>
> >
> >
> > Sent from my iPad
> >
> >> On Aug 12, 2021, at 12:57, Joe <nss at mwt.net> 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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>
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