Micro PA100 users...

[John Shoffner]

Question for those who may be using the PA100 ;

Just put one in-line today with the HL2.  My particular amp delivers 100w at 2.3w in. It makes 37w at .7w in (Hermes min power).  It will for sure go toward 200amps at full Hermes power.  

Also, watching the temps of the four mosfets on the PA100 board,  three run identical temps.  The fourth (far right when looking down with rf connectors at top) runs 20deg less.

In an act of bravery, I swapped out all four fet's with fresh versions and got the same results .

Any body else seeing this?  Otherwise, the amp seems fine.

73, y'all

 John 

Ko4mjc

[randol...@gmail.com]

Good deal on the new 100 watt flavor. I have been using a modified Micro PA50+ for over a year. I need 30 watts to drive a dual LDMOS amp. I had to change out the Mosfets to real RF parts since the PCB was aready laid out for them and MRF186 parts play well and you can run AM and FM without any heat deaths. I see many deaths reported ojn the Facebook support site. The Mosfets are designed for switching powe supplies and AM/FM duty is not wise.

Randy

[Jim KD4YLQ]

Hey Randy,

                   my pal Mike KM4KY has been using a PA50 for FT8, but it burned up a day or two ago. Can you share more about what you did (i.e. new MOSFETs) or where you found the details of to make yours more reliable? I'll pass it along to Mike , or you could do that yourself if you'd prefer. Thanks!

73  de Jim KD4YLQ

[randol...@gmail.com]

I wrote this up on his Facebook with a picture of the single BLF86 change to a real RF transitor -beautiful overkill and the PCB was laid out to support this LDMOS.

https://www.facebook.com/groups/6090995314269480/user/61559698417691

[randol...@gmail.com]

Correction, MRF186 not BLF186.

From Facebook post:

The most excellent PCB design supports this easily. All I had to do is change R1 and R4 to 100 ohms, 3 watt and set gate voltage to 5.000 vdc. I had to drill and tap the heatsink for the flange mounting screws. I did not have to add additional drain-to-drain capacitance for 10m and 15m.

The MRF186 data sheet shows IDQ values for 100 watt, 900MHz 28vdc so operation at 13.6vdc required some testing. I found that a gate voltage of 5.000 vdc plays well, nice and linear from .2 watt to 5 watt input. Indicated temp can now raise 5-15C and output only raises 0.3 watt vs previous 2x.