Post
by Albert H » Fri Aug 11, 2017 3:07 am
You're running it slightly beyond its official rating - maximum dissipation is supposed to be 17.5 Watts, with Pout=8 Watts. Collector current is meant to be 1.25A maximum. I've used them at around 10 Watts to drive a BLY90 to a little bit over 50 Watts, back in the bad old days of 12.5V bipolar transistors.
I built a series of rigs with BSX20 oscillator, BSX20 buffer, BSX20 doubler, a second BSX20 doubler, a BSX20 amplifier to about 100mW, 2N4427 for a Watt, BLY87A and a BLY90 final. The oscillator ran at ¼F to be well within the range of cheap logic ICs for the PLL. In those days, prescaler ICs that would work in Band II were expensive. Each doubler had two critically coupled tuned circuits and the output was surprisingly clean when correctly aligned. The PA had a HUGE heatsink since the amount of heat generated by the driver and output stage was enormous. The supply leads had to be pretty heavy duty, too!
I used diode programmed 74HC CMOS logic - a 74HC4060 for the crystal oscillator and divider, a 74HC4040 for the preset divider, and a phase comparator made from a 74HC7474 and a 74HC7400. There was a passive loop filter, and the phase comparator gave solid locked / unlocked output which was used to enable the PA power switch - the link receiver would switch the PA on when the link was established.
This style of 50 - 60 Watt rig was used a lot in the late '70s and early '80s.
"Why is my rig humming?"
"Because it doesn't know the words!" 
