Re: QCX was OK #chat


Hi Steve
Well, your problem is very similar to mine.
However When I first powered up and aligned it all was fine.
But after probably around 1/2 hour of sporadic CW TX and WSPR TX (got signals across the pond at 20:00z)  I noticed the power was fluctuating a bit like only 0.5 a watt variation.
Any way I switched off and the following morning the same problem as yours.
After a few e-mails with Hans I got the power back. It turned out to be Q6 that had failed, I was also using a duff dummy load which didn’t help. Originally my dummy load was ok. Some how it got swapped for one O/C, FINGER TROUBLE.
I like you saw similar wave forms at the gate, Hans said that was due to the 50MHz scope I was using but he was concerned  about the levels.
I changed the MPS 2907 for an MPS751. My TX was restored. A good 5W out.  However!! at initial key down the TX draws 1.0A with about 1 watt out, re key and its fine again. I found that there was 13 v on the drains at initial key down and after keying once that returned to 0v.
I have asked Hans about this anomaly but still waiting.
However mine has gone to pot now. I decided to carry out the re-alignment process, NO 700Hz  during the alignment just a horrible noise coming from the speaker and none of the adjustments vary which you may expect. To add to the problems I can still get 5 Watts out but the CW note is terrible.
This one has taken a large amount of time and have put it on the shelf for a while.
Will look at it again with a fresh outlook on it. But to date a bit disappointed with it. Mine is the 17m version.
Hope you get sorted.

From: Steve
Sent: Sunday, October 15, 2017 12:11 AM
Subject: Re: [QRPLabs] QCX was OK #chat
Hi all, got my QCX up and running on 30m and receiving very nicely but only with about 1W power output on tx. I confirmed about 23V p-p on the drains of the PA transistors. I only get about 3.5 p-p on the gates, so it looks like low drive. The gate waveform is not a clean on-off but more of a triangular shape so that's not right either. On tx the rig draws about 350mW and the PA transistors get warm to the touch.

I've seen some similar issues in various posts, but so far nothing conclusive. Just wondering if anyone has found a fix to this.


Steve MW0KST

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