[Amps] Need Smarter Than I Am Help.

[Joe Subich, W4TV]

<http://www.arrl.org/files/file/QEX_Next_Issue/2015/Sep-Oct_2015/Kaune.pdf>

73,

    ... Joe, W4TV


On 2021-10-08 11:10 AM, Joe wrote:
> As many of you here know, I have been making some MAJOR changes to this 
> Heathkit SB-220 amp.
> 
> Many here, and many other places, have helped me both on these E-Mail 
> lists as well as directly.
> I am extremely grateful for all this help!
> These awesome people have given this guy that sometimes just does not 
> understand something a LOT of help.
> 
> I won't waste space here, unless people here want the details.
> 
> But I need help with the final last steps on bringing this AMP back to 
> life.
> The AMP works, I just want to make sure it is working correctly or in 
> it's best way.
> 
> The help I need with is because of the last major change I have made to 
> this amp was the High voltage section.
> It is totally re-built, with a Major change. The High Voltage is now 
> roughly 3600 volts.
> This increase of voltage has thrown The Pi-Output network all out of 
> whack, because of the Plate load impedance has changed sooo much.
> 
> So the first thing I want to confirm, is my calculated value of what the 
> plate load resistance
> will be for a pair of 3-500Z's running at that voltage. For when running 
> the reverse path output network testing.
> You know, lift the plate caps off the tubes, and at their common 
> connection where the two parasitic suppressors join,
> Run this value of resistance to ground. Then you can activate the T/R 
> relay, and using a VNA, or like an antenna analyzer,
> you can actually adjust the Pi-Output network to get a min SWR, so now 
> you know where the whole system matches and is happy.
> 
> Obviously to make this test meaningful, I need to be positive, what the 
> value of the resistance to ground should be.
> So Looking for these second opinions of what that value should be. And 
> if you wish, explain how you got that value?
> 
> Now, at least that above question, I am fairly confident on the value I 
> have calculated is right,
> or at least close enough it won't make that much difference.
> 
> But this next one, or two, kind of co-related, I am 100% confused about. 
> A few have tried to help,
> but it is like they are speaking a space alien language.
> 
> OK the amp has Standard old Eimac 3-500Z's a pair of course.
> Stock Caps on both Plate and Load.
> 
> The Inductor Now is a 0 to 18uH Roller Inductor.
> 
> The output side of the bandswitch, the ONLY thing it does now is to add 
> the C56 Cap to ground when on 80 Meters.
> 
> Now here is the confusion.
> 
> I have had Tube gear all my Amateur life since 1975, Drakes, Heathkits, 
> etc. And amps, Drakes, Heath's, Henry's etc.
> 
> And when tuning them up it has always been that the Plate cap amount of 
> "C" always depended on the frequency of use.
> 
> On 10 meters it was hardly any "C" at all. And as you went down in Freq, 
> you would have more and more "C" being used.
> 
> And that's the issue! On 10 meters, With that Roller Inductor, I can get 
> a perfect SWR and I mean PERFECT, 1 to 1, Not even 1.01 to 1, but 1.00 
> to 1.
> 
> BUT..... and there always is a BUT isn't there?
> 
> I can get this perfect match, with a Plate load Cap fully un meshed (min 
> capacitance) and easily as far as 50% meshed (like where it would 
> normally be for 40 meters) and anywhere in-between! just by using a 
> different amount of "L".
> 
> What is the "BEST" setting? I mean it is a perfect match, but running it 
> with the cap like it would be for 40 meters doesn't seem right even tho 
> the match is perfect.
> 
> So then I am told this is correct, but it all depends on the amount of "Q"
> 
> UG! "Q" This I have spent countless hours trying to understand and still 
> can not seem to grasp what "Q" is?
> 
> What makes a "Q" of 10 a "Q" of 10.
> 
> If you want a different value of "Q" What do you change to make the "Q" 
> change?
> 
> How about even a simple question,,  How do you measure to learn what 
> amount of "Q" is happening?
> 
> And I guess a Important question,,, What level of "Q" does someone want 
> to have in an AMP like this?
> 
> I hope someone is willing to try to help this old fart to try to either 
> understand this, or at least help me be an appliance op and just get it 
> set right so I can use it safely for the amp he he he.
> 
> Anyone?
> 
> Joe WB9SBD
> 
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