I have done a bit more testing now using an RD16HHF1 pair in the final although expediency meant i used the final section of the G6ALU 20W pa design.
I also found oscillation problem (about 110MHz). It seemed to be coming from the 1st and maybe the 2nd stages of the MPSH10 stages. I removed the 330pF from the 1st stage and it's now pretty tame. BUT, the response is nothing like as flat as I had hoped it would be. I have no feedback on the RD16HHF1 stages as yet. I don't run the drive control flat output though as looking at the output on a scope, it's severely flat topping with this level. Around 16-17W is about max. level.
But I did plot the response of an original complete G6ALU amp and it falls away badly at the 80M end of the HF bands. In the PicaStar where this pa is used, it's no problem as Star has software drive control on each band since its DSP based.
Not much time to investigate further at this stage.
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.
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