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Evan,
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I wasn't shooting for the correct inductance for each winding of T501.
All that matters is that the ratios of those inductances are correct.
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> The inductance value affects the power output compared with and without L502.?
> I suspect this is due to the flux storage in the higher-inductance cores.
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I might expect that to be an issue on 160m and 6m, but not something I'd expect?
on 80m.? What frequency are you testing at???
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Here's data on the BN43-202:? ??
Says inductance of a winding in uH is:? 2200*(turns**2)/1000
But they don't specify what a turn is.
That dual aperture core works as two independent toroids, so they could figure?
one turn to be one pass through one hole, or one pass through both holes.
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I got lost in the weeds a bit figuring out how to find the inductance of a center tap winding for LT-Spice
given the inductance of the secondary winding.? Best to just do what you are doing,
take the number of turns for that winding and the AL value for the core and compute the inductance.
You will arrive at the same inductance ratios as I did.?
The AL value is not critical for simulating a transformer in LT-Spice so long as the reactance
is an order of magnitude greater than any loads hanging off of it.
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I did notice that the inductance ratios you had in the adjusted T501 of QMX_L502_sim01_w3_2.asc
were correct for?a 3:1 turns ratio transformer, not a 3:2 transformer:? ? 2*sqrt(4.2)/sqrt(1.9)=2.97
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The reactance of T501 windings varies by considerably more than an order of magnitude?
when we try to use the same T501 from 1.8mhz to 54mhz.
What's more, things work best if it can pass the first few harmonics.
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Anyways, the big news is that blowing the BS170's from over-voltage on a 12v build
may be cured by going to the same 1:1 T501 that is used on the 9v build, but removing L502.
This is shown in the "Stock without L502" simulation in QMX_sim04.asc that I posted yesterday.
I'll try that out in hardware when I get a chance, see what blows up.
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There are lots of other things we could try, but that's the most painless solution
that I see possible.
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A clean push-pull RF amp would be either VMCD or CMCD as demonstrated in the last two
simulations in QMX_sim04.asc.? What we have now is a VMCD getting force-fed a constant
current through L502, which will indeed cause Vds voltages to get out of hand.
But there are all sorts of compromises to be made in getting something to work at all
from 1.8mhz to 54mhz, and I can believe that the current design was found to work better
on the bench than a clean VMCD.? The current design may well turn out to work better than
what I am suggesting, will be interesting to see how this sorts out.
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Jerry, KE7ER
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On Fri, Feb 28, 2025 at 12:00 PM, Evan Hand wrote:
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