Thanks Bob.
Well, all but one amp are toast. The first one I powered up was the one
with the RF3809 chip. I had a (well tested at high frequencies) 20dB 200w
attenuator at the output followed by 30dB 3W attenuator and a 50ohm
terminator. The input was terminated. When I gave it 14V limited to half an
amp the output inductor went up in smoke. The chip was shorted. Oh well,
here goes $5...
Next one got my hopes up, because it actually worked when I gave it a
-10dBm and then 0dBm and it showed me over 1W of power (which is what I
need), at 2~3dBm and the output transistor burned up immediately :-( (this
is despite the radiator). These are rated at up to 10dBm input allegedly
and 2W of power.
The next one was a disappointment. It looked the best but it run at measly
23dBm at 450Mhz.It did show about 1W at 140mhz. So it went into a drawer.
The final one looked nicely in its cnc case and boasted 3W at 1MHz up to
750MHz. This one actually worked. I put it on a big radiator which kept the
heat down and I played with my 1W of power for 2 days. Until it just
stopped (the sdr outputs a max of 7~8dBm, I had a dc block between the
devices,to protect the sdr just in case). Upon opening it turns out the
output transistor burned up.
And now I did some research and I found all the devices essentially use the
same output transistor marked K2 or KB or K5 in sot-89 package. It is a
Mitsubishi RD01MUS1-T113 or MUS2-T513. All of them are rated at "over 0.8W"
with maximum power dissipation of 3.4W and efficiency of 60% to 70%. So no
surprise they burn up very quickly when the entire device runs at 500mA at
14V. Let's subtract 150 for the first stage. That leaves almost 5W of
thermal power for the output. No wonder it burned up when it was asked to
go over 1.x W
All if these 2W, 3W even 4W sellers are scammers sadly.
73, Lukasz
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