An SB-200 question - high SWR

[VE3FMC]

I have an SB-200. The input SWR is about 3:1 on 80 Meters. The other bands are fine. This amp has new tubes, so that is not the issue.

The tech who put in the Harbach mods before I bought the amp told me he tried adjusting the input slug for 80 meters and could not get the swr much lower.

I use a tuner between the rig and amp to satisfy the rig. I realize this is not the best fix but it works.

Maybe during the winter I will try to adjust that input swr on 80.

As someone said, this amp was designed and built when tube final rigs were being used. The Pi Network in the older tube final rigs were a lot happier with a higher input swr than the modern rigs are.

I ran this amp with a TS-520 and after tuning the amp I would reload the rig and all was fine.

[N7DM]

Boy... I had a SB-200 on a ship in 1-9-7-1 !!!  Bullet proof, as long as I could 'dip the plate'.  Of course, Pi-Nets were famous for loading Nails and Locomotives; lousy for Ham Antennas. Balanced feeders common then. I never had the finals 'go flat'... just drive it and DIP THE PLATE.

73  ...

[N7DM]

Sure hope your '200' is working out for you, OM. Brings back a lot of memories. Mine fed around 60 feet of 'vertical' wire, up to the Main Yard. Loaded to 'the mark', against the ships hull floating in all that nice salty warm water. The 'Pi' loved it and I ran hundreds of phone patches back to 'the land of the big PX and the multi-colored taxi-cabs', both on 20 and 15. Good Ham times...

Tnx for the 'remind'... ES  73

dm

[WA6NEQ]

An update for all who replied. I was able to find two supposedly NOS Cetron tubes from separate sources. Installed them in the amp, turned the amp on and let it sit for about 8 hours (I've heard that this is a good practice for tubes that haven't been used for some time, not really sure why). Tuned it up on 80m and have 600W into my dummy load. SWR of 2:1 seems a bit high still, although an improvement from before. I had previously tweaked the coil slug and didn't try to tweak it again. I haven't had the chance to check other bands.

Thanks to all for their comments  - 73 - Bill