Re: RD16HHF1 power curve flattening...some

K9HZ <bill@...>

Hey Nick… did you make any progress?  I’ve been dying to dig into this but work keeps getting in the way of playing with my radios.  That’s gotta stop!


Something is up.  You can actually put another secondary winding on the PA transformer for negative feedback… That’s actually preferred.


I ran a couple simulations and the whole thing is stable without the feedback though (slightly lower gain though).


I sure like the 20+ watts out of those RD16 HHF1’s though and they are bullet proof.  I’ve never blown one out, and I’ve designed a lot of amplifiers with them and made a lot of mistakes with the “ON” switch in the “GO” position.



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email:  bill@...



From: [] On Behalf Of Nik VK4PLN
Sent: Sunday, March 11, 2018 6:55 PM
Subject: Re: [BITX20] RD16HHF1 power curve flattening...some


Well, i have dont my mods and powered up. Results are mixed:
Here are the mods.
RD16 replace IRF510.
New output transformer 1:4 BN43-3321 with a 330pf cap on input.
feed back resistors. from 22ohm to 1 K ohm
piggy backed R87 and R88 with 220pf capacitor.
RV1 full drive.

So results.
80M - 20W + ( blew my 2 Amp fuse)
40M - 18W - Seems stable.
30M - 17W BUT I get BAD feedback/ oscillation by just going PPT with no voice. The watt meter goes up to 18W!
20M - 15W  -  Same feedback issue
15M -  Same feedback issue.
10M -  Same feedback issue.

I have been thinking ans looking at other RD16 schematics, in alot of cases they dont use the feedback on the finals?
Also could this issue be cuase in the driver stage?

THanks guys, I am in over my head here....

10M - Same feedback issue


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