1.5 KW SolidState AMP

Pair of BLF189 LDMOS in Push Pull Class AB

July 2018 1.5 KW Amp Project

Started collecting parts for a Legal limit solid state amp:

3 KW AMP deck purchased on EBay.
I drilled and tapped the 1/4 inch thick copper heat spreader they supplied
and mounted it on an aluminum heat sink.

Surplus 50 VDC 60 Amp power supply $60 on EBay, Bought 2 so I have a spare.
They were originally intended for 48 volt power system used in Data Centers. they can be paralled for higher current or or connected in series for higher voltage. VERY well made!

Inside the 50V 60 amp Power supply:

I added this box with a 12v control relay to switch the 240V on and off from a switch on the Amplifier front panel.
Also it has the 50v enable circuitry for the PPT signal; the 240V power cable and 50V 60 Amp cable to the Amplifier:

Amplifier control board built from kit from W6PQL. (Jim Klitzing https://www.w6pql.com/parts_i_can_provide.htm)
Provides PTT power up staging for amplifier, fan control, Hi Temp and Hi SWR lockout, ALC lockout while switching.
It also drives front panel LED indicators to show status states. I learned that I COULD build boards with SMD parts.

This Hot Air SMD rework station along with the Chipquick Solder Paste (Sn42/Bi57.6/Ag0.4 in 5cc Syringe)
This makes building circuit boards with SMD parts MUCH easier!!!

160 - 6 meter 2 KW low pass filter board I built from a kit supplied by W6QPL. (Jim Klitzing http://w6pql.com/images/hf/lpfgen2.pdf)
Here I am testing it to make sure that it meets specs.

Pair of 100 Amp meters with shunt,
I'll convert one of then to 100 VDC to monitor my 50 Volt 60 Amp power supply feed to the amplifier deck.

January 2019

I finished debugging the amp, and got it set up along with the rest of the station so I could try it out.
Here it is next to my ALS-500 and MFJ IntelliTuner.
Made my first contact, Don NT5Q and a signal report from Charlie KG5WTQ. Charlie said the audio sounded OK!

Here are some more pictures of the Amp:

Here after a test where I blew out 2 of the BLF188, and I found the SWR detection circuit wasn't working properly.
I replaced the BLF188's with BLF189's, a little more rugged version of the LDMOS part. "A 1900 W extremely rugged LDMOS power transistor" from the AMPELON web site.

The filter board is mounted under the heat sink.

3/20/2019 It became apparent the fan / heat sink arangement was inadequate to cool the transistors at full power.

I moved the fan from the end of the heat sink to directly under the middle to get the maximum cooling in the area below the BLF189 LDMOS transistors. The fan is a 4000 RPM 200CFM high pressure fan, so it blows amost a gale out of each end of the heat sink. It also makes noise like a jet engine!!! I added a three stage fan speed control. The fan runs at low speed when PTT is active. If the heat sink temp gets up to 115° f, the speed increases to medium. If the temperature reaches 140° f (60° C), the fan increases to maximum speed and the transmit is suspended until the drops to 130° f.

I also added a low speed low noise fan to the top of the cabinet to remove the hot air from the interior. This fan runs whenever the power is turned on.

Back Panel

Here is the completed amplifier in use. The Scope on top is showing the rf output from the previous SSB transmission (yellow trace) and DC representation of the envelope (magenta trace).

In early 2019 I decided to add a Data Aquisition module to better understand the operation of the internal circuitry.

Here is a screen shot of the info from the Data Aquisition module: