I took delivery of a Micro PA50+ amplifier this week and have given it a couple of tests in the shack. Early reports posted here about this amp were not favourable but I think the latest version is much improved although it isn’t fully sorted.
My first impressions were not good as I thought it was broken. I couldn’t manually select 30m and on 15m it acted as if it was turned off and just let the few watts from the IC-705 pass straight through to the antenna. On the little screen BYP appeared when 15m was selected which I guessed meant bypassed but the very thin manual makes no mention of this.
Fortunately, there is a Facebook group for this amp created by the designer who posts advice on how to sort issues. From this I learned 15m and 30m are turned off by default for some reason. Pressing the Fn button 8 times and then turning it off and on again enables these bands. It still won’t allow me to manually select 30m but it switches to this band automatically if you give it a 10MHz signal. I suspect this is a firmware issue which will be addressed at some point. I’m not looking forward to updating the firmware as the procedure isn’t very user friendly. The 8 presses of the Fn button are not mentioned in the current manual which has not been updated to reflect the latest firmware version, which is 2.8.5 in my case. In the manual 8 presses does something very different.
Having destroyed a LiFePo4 battery earlier this year on an activation by drawing too much current from it I made up a shunt rig to monitor the current. It isn’t for field use but it has told me that at around 30W the Micro PA50+ is drawing a little over 4 amps which is well within the 9 amps limit the 6Ah battery I have now claims for continuous discharge. I forgot to see what it drew on 50W today, just sticking to 30W but I will try 50W soon.
My 30W tests so far using SSB (a 59 from Italy - although this might have been a contest 59 
) were encouraging. CW was, as you might expect, reaching out well according to RBN but occasionally the IC-705 showed a very high SWR for the briefest moment on first touching the key. Increasing the Bkin delay to 500ms seemed to tame this but this is something to keep an eye on. I saw the same when using a dummy load so this wasn’t down to the antenna but something between the radio and the amp.
I ran FT8 and FT4 today and managed a QSO into South Africa and was heard in Singapore according to Pskreporter.
The fan on the amp is noisy and runs continuously when using a digital mode. This shouldn’t be a problem on an activation but it would be irritating if this was your shack amplifier.
The latest firmware seems to have overcome the high SWR problem reported by others with earlier versions. One of the photos shows it running without problem with an SWR of 1.6. This was because the coax from the dipole was running almost parallel to one of the dipole legs and when I changed to 20m the SWR shot up to over 3 which triggered the SWR protection built into the amp. I didn’t intend to do this but it was useful to know it shuts down with high SWR but not at lower figures.
I will emerge from my winter hibernation and give it a try on a summit soon.
Random photos of today’s test are enclosed. The Facebook group is:
