Hardware finished?

I think the hardware is more or less finished now but my projects are seldom ever completely finished, especially when it comes to software. Here's some pictures of the finished article

 

 

There are still various "improvements" to make but most of these are in the software and it's tricky to take pictures of software...

• Removal of the tacho monitoring software - I can't find a way to keep RF out of the fans, which are, after all, right up against the "hot" parts of the amp. This is no great loss - I had vague plans of monitoring fan speed to create a control feedback loop but that is provided perfectly well by monitoring the heatsink temperature and setting fan speed accordingly.
• Consolidation of fan speed control to a single output for both front and rear fans. In the end I couldn't think of any situation where I would want to control them separately, so the code can be simplified. If I do produce Mk II controller PCB it too can be simplified somewhat with the removal of a couple of transistors and associated passive components.
• Removal of bias control. In fact I never wrote any code for this as in the end I couldn't see any situation when I would want to have the amp powered up (50V supply on) but not biased. There would be a small reduction in power consumption on receive if the bias was turned off but then there is the question of stabilisation of the bias at the same instant as RF is being applied. I don't feel the need to go there.
  
• Calibration of the power meter. This really needs me to gain access to a calibrated RF power meter somehow because I have nothing that can measure 400W at 144MHz. If needs be I will rent one some time. It's not really too important, as I have an approximate indication, probably within 10% derived by measuring input power and multiplying by device gain. The 50V power input current provides a useful cross check and seems to be consistent.
  
• General ongoing software improvements as I get more experience with actually using the amp - probably a never-ending project!

I fixed the problem of RF getting into temperature sensor logic by cutting a track on the PCB and inserting a 100uH choke with 10nF to ground. Good as gold now. Not worth commissioning a new PCB for that!

So I think I have a usable amplifier. It runs reasonably quiet and cool and local reports are that it is clean, so I shall install it as part of the station once I can find a space for it!

Updates to this Blog will likely be rather less frequent from now on, though I will try to remember to provide occasional updates as the software changes or other improvements come along.

I hope you have found the Blog interesting and comments are always welcome.