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Muhsin,

?

Your post 111673 was a bit strong for a problem that’s only been recently solved. Yes, you were correct in the technicality and of your post. Hans has clearly indicated that all new radio shipments include the RWTST transformer. As with all new designs, reporting issues gets them fixed sooner or later. There was no shame in the original transformer design and it’s great that Ross came up with a new design that improved upon the original transformer. Chalk this up to experimentation that leads to improvement.

?

Tony

AC9QY

You might have misunderstand me

My message should be read as Ross's RWTST is "It is so good that it should be banned"?

73

muhsin TA1MHS

Plating is effective in VHF and above because the skin depth is shallower than plating thickness. Litz wire is effective from 500kHz to about 3 or 4MHz max but ineffective above. So, for a good part of HF, we really have solid copper and good construction as the only option. Those copper clad steel wires are good for VHF and above but not best for HF.

The loss of a well built capacitor is mostly determined by the dielectric loss (tan delta).

lest they desolder themselves.

The challenge for such a low impedance tank circuit is that the current flowing through the caps.

Another way to put it: silver mica 200pF 500V has twice the area of 100pF 500V but the rest is the same. In other words, 200pF is essentially the same as having two 100pF in parallel packaged as one component. The loss of a well built capacitor is mostly determined by the dielectric loss (tan delta). The Q of those two capacitors is practically the same.

Maybe I can make it in a contrasting statement for illustration. When you are dealing with RF bypass, DC block or similar purposes, you don't really care what the Q is as long as the total impedance is low enough (i.e. adequate C with low ESR). Similarly, when you are making an RFC or common mode choke, you don't really care much about the R part as long as the whole impedance is high enough (in many cases, such as EMI/RFI reduction, high R is even desirable). However, in a tank circuit, the question is Q=X/R. Putting caps or inductors in parallel always scale both X and R so there is no net change in Q.

As I said in the parentheses, the R and XC both decrease but the Q is the ratio XC/R, which remains unchanged even if more caps are put in parallel. The same thing applies to inductor's component Q, XL/R. The main point is that it is very tricky to build a very low impedance tank circuit for power amp and keep its loss reasonably low enough so that the heat dissipation is manageable.

Hans-

I’m excited to say the least. I have the assembled list open in a tab all the time and I’m looking forward to seeing my order number disappear from the #1 spot.?

Chalk this up to experimentation that leads to improvement.

Hi

I totaly agree

improvement, Yay :)

73

muhsin TA1MHS

The tricky parts of this amplifier is the output side.

First of all, they used an L-match to bring 2ohm to 50ohm. That's a very high Q for L-match. It can be done but the components must be very high Q to avoid significant loss (i.e. heat). From the photo they appear to have used a copper ribbon or similar material to reduce the loss.

Now the output transformer is a conventional transformer with 1ohm load on each transistor. That transformer must be flowing 25-35A of DC current total and RF current on top of it. The ohmic loss must be kept very low, again what appears to be copper ribbon looks good enough for it. The challenge for such a low impedance tank circuit is that the current flowing through the caps. Usually, component Q of capacitors are several times better than well constructed inductors, but when the impedance is this low, it gets tough for the caps. They used 19 caps in parallel, which certainly increases the current capacity of the combined capacitor but it does not increase the Q at all (Q is XC/R and both XC and R scale as the number of parallel components increase) so still some power is wasted as heat. That's the challenge of dealing with a very low impedance in tuned output network.

If they operate this amp with a 12V supply, even with a bad SWR, these drains probably won't see more than 50V. But that's also what's making the output network very much of a challenge. If they used a high voltage RF device and operate the amp with 48V or 36V or some higher voltage supply, things would be a lot easier (but then you wouldn't be able to use cheap transistors).

The component numbering convention in that article is confusing to say the least.

What they say L2 in the schematic (but not the caption under the schematic) and text appears to be labelled as T2 in the photo. What they say L5 in the schematic seems to be labelled as L2 in the schematic caption and also in the photo. T2 looks like 1:1 conventional transformer with a center tap on the primary.