>Here is an update on my 80 meter dilemma on my SB-200. Originally, I posted
>that my SB-200 was working great on 40-10 meters but not good on 80. I had a
>high swr and any noticeable power output above 150-200 watts immediately
>dissipated.
** This suggests that your drivermight be throttling back to protect
itself.
>
>The load and tune Caps (both the 100 pf and 500 pf caps) test good. No
>apparent damage to bandswitches. The Plate choke looks good.
>
>I inspected the tuned input C30 cap and added an additional 200 pf to the
>470
>pf mica cap. My swr on 80 meters is now much improved. I now have noticeably
>greater output power BUT the power still quickly dissipates or diminishes
>while keyed down. It peaks then quickly drops.
>
** strange
>Are my grid-ground caps off both tubes suspect? I do have two well worn
>tubes that show excessive heat damage. Can the 572B tube work great on 40-10
but
>become dysfunctional on 80?
** No.
- I would try a Pi-network 80m tuned-input with a Q of 2. (Xc!=25-ohms)
good luck, Don
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