[SPAM] [BITX20] LTSpice simulation of uBitx Power Amp

K9HZ <bill@...>

Jerry… thanks for doing this.  I had intended to do this same thing but so many things kept getting in the way.  Since you uploaded the .asc I’ll try some of my favorite PA transistors in place of the 510s when I get back from vacation and see how they look.  The 3904s should be good above 50 mhz. also I suspect the stages are coupled a bit too tightly at higher frequency where something smaller would be more appropriate.  Anyway, nice work.


This does point out a few “oh yeah” things though.  The 510 miller cap loading at the higher frequencies is very high.  I guess you see that in the smith chart of the spec sheet too so no surprise.  Also, I think we see a lot of variation in the 510 parts…as some people report them working well at 20+ MHz and some not so much.


Yes agree.  I’d love to see a sim of the WA2EBY amp.  Dying to know the efficiency at 30 MHz.



Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ


Owner - Operator

Big Signal Ranch – K9ZC

Staunton, Illinois


Owner – Operator

Villa Grand Piton – J68HZ

Soufriere, St. Lucia W.I.

Rent it:

Like us on Facebook! facebook icon



email:  bill@...


From: [] On Behalf Of Jerry Gaffke via Groups.Io
Sent: Thursday, February 01, 2018 3:24 AM
Subject: [SPAM] [BITX20] LTSpice simulation of uBitx Power Amp


I've uploaded an LTSpice simulation of the uBitx Power Amplifier from Q90 on out through the IRF510's
but not including any of the transmit low pass filters, can be found here:
A pdf of the LTSpice schematic is here:

I ran several simulations, all with a 0.05 volt pk-to-pk sine wave driven into C80 at the base of Q90.
Anything much higher and there was some definite gain compression going on.

With the IRF510 gates clipped out of the circuit, I saw 7.7v p-p of drive for each gate at 30mhz, 10.0v p-p at 7mhz.
Note that these signals were still loaded by the 47ohm resistors at R97 and R98

With the gates restored and the IRF510's powered from 12v, the gates had 3.0v p-p at 30mhz, 8.0v p-p at 7mhz.
Simulated power out (computed from the unfiltered p-p voltage into 50 ohms) was 5W at 7mhz and 0.9W at 30mhz. 
Will be interesting to see what this does if the gates are driven harder.
Also interesting to try a simulation of the WA2EBY amp using the same IRF510 models.

Jerry, KE7ER