W6PQL amplifier is great modular amplifier design. Since I had homebrew assembled in 2015/16, it has proven very solid and reliable. I have some issues with Directional coupler and detection of signals to represent reverse power accurately as per Jim's design. However, other than this aspect, i have used the amp in many contests and activations. Last year(2022) during CQWW CW contest, I realized that sequencer is slightly slow in switching back to RX from TX mode. Some of the stations I did not copy either first character or sometimes missing dit or dashes of the first character. This was not serious issue, but anyways, once you know what adjustments to do internally, you tend to tweak it towards perfection. I tweaked the timing so that its faster switching in sequence.
During the CQWPX SSB contest i did not realize any issues. And after all SSB signals are delay start by human nature of speaking into mic. Also, problem of hot switching might have started during the WPX SSB itself , but did not come to surface. During WPX CW, My entry was bit delayed due to exhausting MQTH work till previous day late night and tr avel related fatigue. VU2VTI was the early starter at VU2REC club station for the contest. When I started on the bands, at first it seemed all ok. But, suddenly started feeling the RX is weak sometimes and delayed to full signals. I thought it was due to some ionospheric disturbance. But when it continued for some hours, i sensed it unusual. Asked VU2VTI to be on my system and run the contest for few minutes. He confirmed that it is unusual and something might be wrong with my Amp or Radio. I then disconnected amp from the path and observed no issues with RX drop. This confirmed me that Relays inside the Amplifier might be damaged. No time to fix and no spare relays on hand. I packed my amp to carry back and continued the contest with TS590 barefoot.
Back at home, after opening the amplifier lids, first thing visually checking the three LEDs in sequence i.e. Hold off ALC line, Trigger Relay line, Release ALC line. Initially it was almost instant, I adjusted PCB variable pot to have some visible lag between the events. There was no RF input given to the amplifier, all testing was done using a SPST switch to PTT in RCA plug. This allowed me to rapidly check the working. Next came checking the Input and Output Relays. While input relays typically take less than 10Watts or less in the path (my drive power), output relays handle upwards of 350W or more.
I had a hunch that output relays might be the issue due this factor. While switching PTT line, keeping my fingers on the relay, I sensed no movement in the output relay. Thanks to modular design of the amp, i could desolder the output relay PCB and test it separately. Found that relay coil was showing higher resistance and was not energizing. This is Omron G2RL-1E relay and fortunately, i had few of them in my spares. I did replace the relay and test OK.
This incident has taught me something very important about sequencer lines and never to be too greedy beyond the design specs. By properly adjusting PTT delay for Amp (i.e RF hold back after PTT switching), we can safely control the TRX path for signals. Typically 100ms is what W6PQL suggests (Hold ALC line + 50ms delay+ trigger relays+50ms delay + release ALC line).
Now will have to wait for next contest or event for my setup testing in real situation.
Hope this helps someone in similar situation.
VU2XE
