Yes, loss in the transformer turns into heat. But that's a different mechanism than what I think is stressing the finals.

On Sep 29, 2023, at 20:54, Paul - AI7JR <paul.hanchett@...> wrote:

If it'll fix it I'll do it. I like building things, but don't like undoing things if there's any way around it.

Copy that! I managed to melt my CPU while doing intial testing on my QMX (I think some clippings got where they didn't belong), so I ordered a second kit.

Built it this last week, except that my ADHD wouldn't tolerate going step by step through the instructions in the assembly manual. I think I got all the right parts in the right places (yet to be seen...), but I exchanged the male and female connectors for JP304/JP206 and JP303/JP205. And in the midst of it all, somehow I knocked C107 off the board (and I can't find it anywhere!)

I thought building a second time would be a snap, though winding the torroids would be tedious. I WAS WRONG!

Good luck with that transformer-- Could you spray it with cold when it's hot, to see if that's whats causing the power decrease?

Just a thought!

73, Paul -- AI7JR

On 9/29/23 18:39, Cliff wrote:

Paul,

Could be. It gets pretty hot, but I've read that is normal, but maybe not.

As a desperate move I've thought about winding the new type.

Let's see now, new finals, drive IC and output transformer. Hmmmm... If it'll fix it I'll do it. I like building things, but don't like undoing things if there's any way around it.

73,

Cliff, AE5ZA

I wouldn't change the transformer unless it's broken. A new transformer of the same type wouldn't change much. (I'm talking about a different design in my previous post.) Same for the driver IC. It's probably ok if you see the output coming.

The Curie temperature of Amidon 43 ferrite is about 150C. I wouldn't worry about it. (I would worry more about the loss in the transformer. BN43-202 should be able to handle 20W easily but it gets this hot with just a couple of Watts.)

Paul,

Could be. It gets pretty hot, but I've read that is normal, but maybe not.

As a desperate move I've thought about winding the new type.

Let's see now, new finals, drive IC and output transformer. Hmmmm... If it'll fix it I'll do it. I like building things, but don't like undoing things if there's any way around it.

73,

Cliff, AE5ZA

On Sep 29, 2023, at 20:33, Bob Parr <parr@...> wrote:

on 2.12 Wind and install trifilar toroid T2.? I followed the instructions and thought I had it right.? The instructions in the last paragraph of page? 34 says to check continuity between each pair of pins A_A, B_B, C_C.? I have continuity there but ALL the pins are connected.? A-C on the same side, A-B across the toroid.? I uninstalled, checked my three wire cable and no shorts.? Then I looked at the schematic and it looks like all 6 pins do have a direct connection... at least to a DMM.? Am I missing something?

Bob
KG5GTE

On Sep 29, 2023, at 20:32, Paul - AI7JR <paul.hanchett@...> wrote:

Could it have something to do with heating in the final's output transformer?

On 9/29/23 17:30, Cliff wrote:

Hey Y'all,

My QMX has been doing well for a few days and quite a bit of use after fixing some solder joints, but now I notice something that bothers me.

The power will stay up for a while until it gets really warm. Then power will reduce somewhat, I expect hot finals will lose some power, that's normal in regular rigs in my experience, however after a while it will lose even more, up to a watt and a half, sometimes more. Cool things off and it's back up.

Measuring the drive to the finals I get 2.505v on one pair and a 2.534v on the other pair. This isn't at the maximum heat, but was showing low power when I shut it down to test.

Obviously the drive should be the same on both sides, and it has other times. Could the issue be the driver IC or one set of BS170s?

Maybe some before the driver? I'm wondering if this is a clue to my issue of blowing finals far too often.

I can change both the IC and the finals, but before I do I wanted to get opinions from the experts in case we can find the "real" issue.

Thanks all for your comments.

73,
Cliff, AE5ZA

Hey Y'all,

My QMX has been doing well for a few days and quite a bit of use after fixing some solder joints, but now I notice something that bothers me.

The power will stay up for a while until it gets really warm. Then power will reduce somewhat, I expect hot finals will lose some power, that's normal in regular rigs in my experience, however after a while it will lose even more, up to a watt and a half, sometimes more. Cool things off and it's back up.

Measuring the drive to the finals I get 2.505v on one pair and a 2.534v on the other pair. This isn't at the maximum heat, but was showing low power when I shut it down to test.

Obviously the drive should be the same on both sides, and it has other times. Could the issue be the driver IC or one set of BS170s?

Maybe some before the driver? I'm wondering if this is a clue to my issue of blowing finals far too often.

I can change both the IC and the finals, but before I do I wanted to get opinions from the experts in case we can find the "real" issue.

Thanks all for your comments.

73,
Cliff, AE5ZA

On Sep 29, 2023, at 20:01, Ryuji Suzuki AB1WX <ab1wx@...> wrote:

I would replace all final transistors. If you routinely experience very hot finals, you might want to consider inserting a bit of thermally conductive foam between the board and the aluminum case. Good ones are about 15 W/mK if I believe the catalog spec. Those good ones are loaded with heavy minerals and it's quite heavy and cool to touch.

Which transformer configuration did you use? What's your supply voltage?