CHN transceiver update

I did some rpairs on the CHN transceiver.

• -X/RX relais was wired incorrectly. Fixed that
• It contains a variable capacitor at the front. It is used to peak output for the 80 meter band.This capacitor was not working correctly. Fortunately I had a similar capacitor in the junkbox box.That one worked OK.
• The IF board needed alignment. Fixed that.
• Improved decoupling of PA board.

HF PA's usually causes head ages. This one is no exception.
I can get 14 watts CW on 80 meters. On 20 meter it was just 4-5 watts. SSB PEP is lower.
at 80 meter I can get 6 watt. on 20 meter it is about 2 Watt max.
In CW mode the signal does not go through the xtal filter. It is much stronger than the SSB signal.
So I need to get some more gain of the ssb signal.

The PA suffered from some strange distortion. At full power It works for 1 second. then the sinus starts to deteriorate. It does not seem to be oscillation. After a small pause I can get another second with a clean signal.
I tried to solve  it using forced cooling. It helped but it is was not enough.

The power transistors  6xBD137 were mounted on a small heatsink. No cooling paste was used.
I think this causes the problem. A hotspot temperature is getting to high. That may be the reason for the deteriorated signal. So I applied some paste.
I also mounted two 10 Ohm resistors in series over the input transformer of the PA.
This reduces the power to 7-8 Watt but the signal is clean. It looked OK even when the dummyload was removed. Usually PA's start to oscillate when I try this.
I don't need a lot of power though. I need only a few watts as input for a bigger amplifier. So I won';t try to getr max power out of it

Things to do.

• Get more gain for SSB.
• Carrier is not suppression is not good om 20 meter. It is quite allright on 80 meter though.
• RIT works but I can not tune  to the same frequency I had when RIT is off.
• Find an enclosure for the set.