On Thu, Feb 27, 2025 at 10:18 AM, Joe WB9SBD wrote:

Made simple, the two wires are 12 ga copper, about 6 inches long.? Open at the far end.
Simple center conductor goes to one wire, Braid to the other.

I was a contractor to Fort Monmouth, home to the Army's E-Labs until the fort closed.??

They had a megawatt-level dummy load for testing power supplies.? It was essentially a swimming pool filled with copper sulfate solution, with a pair of huge graphite electrodes.

There was a crane which moved the electrodes in and out of the water to vary the load resistance.? Just a bigger version of WB9SBD's.

73, Don N2VGU

Very clever!? I'd love to see some details for the transformer build and maybe some pic's of the details of the chalk box build, if you have time.? No counterpoise?

Evan,

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You are correct, I missed the 100pF cap.

Thanks.

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I had noticed that computed values for L508 and L512 were different than the ones Hans had said he simulated with.

I figured since I was simulating may as well go with those, and that final windings got adjusted when he was looking at hardware.

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I have made both adjustments to the simulation in the attached file QMX_sim03.asc

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Will try your 3:2 12v transformer, but haven't yet.

In simulation it may not make too much difference, I'd expect that all the voltages after the transformer just go down by that ratio.

From forum posts, it seems people have fewer failures of the BS170's with a 9vdc build, so I figured I'd start with that.

However, perhaps that's only because most people have built for 12vdc.

It does seem that with the higher currents of a 9vdc build we would have more trouble with overheating in digital modes.

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Here's the voltage readings from LT-Spice for my original QMX_sim01.asc simulation before and after your changes.

Curious that adding changing the L508 and L512 values brings the output down, but adding the 100pF cap brings it most of the way back up

Output: ?

? ? ? ? ?18.6v as in sim02
? ? ? ? ?15.6v when adjusting L508 and L512 to AL*(t**2) values of 1.875uH and 1.452uH
? ? ? ? ?18.4v when 100pF added
? ? ? ? ?18.4v when both changes made

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I then looked at that final version with both of your changes, and compared it with the same but without L502,

and also my VMCD and CMCD versions as in the attached file QMX_sim03.asc.

Since Vds-peak values can blow the BS170's, I also looked at peak voltage on one of the drains.

Note how much lower Vds-max is for L1-removed and VMCD.?

L1-removed is effectively VMCD, but using the stock LPF which I am still unsure of.

L1-removed and VMCD both also have low output power, which is a function of the square of the output voltages recorded above.

If we were to increase the transformer ratio of the L1-removed version such that Vds-max was equal to that of the stock QMX,

it seems the output voltage should increase to a value of 13.8*(33.8/18.4) = 25.35, which is way beyond the stock output voltage of 18.4

That's the reason I was sucked into this, removing L502 may help with the over-voltage issue at the BS170's

though this may bring on issues due to higher peak currents.

Like all things around RF amps, it's considerably more complicated than one might think at first glance.

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Anyways, I was up half the night here with a hacking cough, which is why I got that simulation done.

Probably time to get some sleep.

Given my current state, could well be plenty more errors in my attempts at simulation and in the above discussion.

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Jerry, KE7ER

On Thu, Feb 27, 2025 at 08:57 AM, ajparent1/kb1gmx wrote:

Generally using that amp at the output of a radio that does

3-5W is barking up the wrong tree.? IT also does not increase the

power enough to be significant (20W wold be a marginal increse)..

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And thank you verry much also AkI. This was exactly what I was looking for.

vy 73 Michael DB2GM

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Hello all

thank you very much for your inputs and comments. The links help me also for future calculations.

vy 73 de Michael DB2GM

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I bought a couple of Hans' dummy load kits (because of their great design) and populated them with different values of resistors.

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For a 100 Ohm load: 10ea. 1K 1% 2W resistors.

For a 200 Ohm load: 10ea, 2K 1% 2W resistors.

Final update...

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I sent it off to Jeff (W1NC)and he turned it around in a couple days. The main problem was the CPU. My guess is the two bad SMPS boards were the root cause, but Jeff did clean up some soldering as well, so I can't rule out the low budget guy working in my assembly lab ;).

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After replacing the CPU he gave it the white glove treatment and got everything working just right.?

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Hey Hans,

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Looking at the , one can be very pleased with the scrolling speed. Your "elves" assemble our much-wanted radios very quickly! We are at the end of February, and they are beginning to assemble the January orders. That's great news—thank you, and keep up the good work!

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73, Joe, DJ0CHE

On Thu, Feb 27, 2025 at 08:08 AM, Dean - KC9REN wrote:

This one addressed both those issues: ?

What is the spare tip situation?? Much of the Chinese stuff uses Hakko tips, if this one does I might look into it.?

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I am also considering this one, which has the temperature sensor embedded near the tip;? it uses proprietary, but inexpensive, tips.??

iron

shorter tips

73, Don N2VGU

On Wed, Feb 26, 2025 at 04:07 PM, Jeff Koenig wrote:

May I ask the name of the font you used for the lettering??

Not the intended recipient, but I use this for my MIL and test equipment builds.?

It is a variation on DIN17, from 1938: ?

The DIN standard, "" has been withdrawn but it is still very usable.

Extremely legible and should be easy to print.

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73, Don N2VGU

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On Wed, Feb 26, 2025 at 04:02 PM, @Ludwig_DH8WN wrote:

I realized changing a STM32 with 100 pins is more fun then a PCM1804 with only 28 pins.

It is a nice feeling of accomplishment when the part "snaps" perfectly into alignment with the PCB lands, almost like magic.

73, Don N2VGU

I should of added, connect your dummy load to the antenna port of the ATU.

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Mel. M0KMD.