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@mwt.net>
Date: 8/12/21 1:42 PM (GMT-05:00)
To: Nidhog <robrk@nidhog.net>
Cc: Amps group <amps@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@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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