Warren, at 50 mhz the neutralization on 572b tubes?is way out in outer space. ?It¡¯s bad enough on 10 meters let alone on 50mhz. ?That said, you can¡¯t expect a dip in the plate at maximum output¡¯. So the proper way to load it is to peak the load and tune for maximum output then try to reduce the grid current a bit and repeak the plate fo maximum output. ?You came much too late to late to this party. ?Both myself and Carl converted many of those SB200¡¯s to 6 meters. ?The trick is to?make it stable at the maximum output point and as Carl said, LEAVE?IT ALONE. ?As long as the plates keep?from getting cherry red you¡¯ll be fine. ?There¡¯s quite a bit of regeneration but the skill in?building them was to keep them from taking off when loaded for maximum output. ?Carl kept his recipe for getting SB200¡¯s to work on ?6 meters as much of a sectet as Mrs. Paul¡¯s cheesecake. ?I¡¯ve probably converted?half as many as Carl did and 18-20 watts gave you?about as much output as you¡¯d dare. ?Keep the output peaked and the plates dark and you¡¯ll be fine. ?This is just another mystery of faith. ?Lou
On Wednesday, December 20, 2023, 7:55 PM, Chuck Neal <cdoneal@...> wrote:
This is interesting¡was this amp modified for grid drive instead of grounded grid??
?
Another possibility is that there could be a bit of positive feedback, not enough to cause self oscillation but enough to generate more gain.
?
Agreed, 18W for 600 W out isn¡¯t possible for a normal functioning grounded grid amp with 572B¡¯s.? Their gain at best in GG is perhaps 12 dB. which would yield maybe 270 watts with 18W drive.? An unintentional positive feedback of 3+ dB would do it though¡.and the tuning would be VERY sensitive.
?
-Chuck
?
From: [email protected] [mailto:[email protected]] On Behalf Of NI5L
Sent: Wednesday, December 20, 2023 7:40 PM
To: [email protected]
Subject: Re: [ham-amplifiers] SB-206
?
Steve,
With no REL PWR function, I have just been peaking everything up using a watt meter. Like you, I am a little bit curious as to why it only takes 18 watts of drive to get 600 out. I just wrote it off to this being a 6-meter VHF amp.? It has a VERY narrow bandwidth... 50.000 to 50.500 according to the plate on the amp's face., which is perfect for me. I have tried peaking the grid and dipping the plate but I come up with some pretty hairy plate current when I do that. I'm just really nervous about killing the tubes or the tank circuit. After reading what Lou said, now I am even more puzzled as to what references to use when tuning this thing. Carl said that once it is tuned, leave it alone and that the frequency range would be covered if tuned at 50,200 or so. I will try what you said next time i get the amp online. Currently it is going to be an off-desk amp when I need power on 6 meters since we have very few 6 mete DX openings like the east coast does. Spotlight openings are few and far between out here in southeast Arizona.
Thanks and 73
Warren / NI5L
