Somehow I screwed up my last response to Carl's reply (KM1H). I meant no disrespect, I should have looked back and noted who recommended the resistor change. My apologies.
Some people have said that 572Bs don't need much air flow . . . Well as posted previously, I would personally recommend having PLENTY of air flow if you want the 572Bs and other components to last. In my FL2000B (same as FL2100) there is a fan under each valve that keeps the air circulating past each valve. But during a contest the anodes end up getting red hot and never get the chance to cool down properly . . . so the whole case also becomes like an oven. Sitting a nice powerful 5 inch fan on top of the case stops the anodes getting that hot, and stops the whole case getting hot and cooking the other components too. If you think about it, you need to get rid of 600 watts of heat (actually MORE with the filaments) . . . think what the air flow from a hairdryer is and that gives you an idea of why you need a decent fan!
In the OP's case, there aren't any other components he needs to keep cool...the RF deck and power supply are separate and the filament transformer on the RF deck chassis looks very beefy, it won't be getting hot. Also, the tubes are vertical and the sides of the deck are open to allow far more air circulation than the Yaesu amp, or the SB-200, could ever have. Using the world's biggest fan won't keep the anodes from getting red, that makes no sense. The thermal impedance from the anodes to the air outside the tubes is close to infinity. You could operate the tubes immersed in cooling oil which keeps the glass at room temperature and the anodes would still get red.
A question somewhat related. Was measuring output power on all 5 bands. Dropped pretty hard on 10 (below 200w) and then realized my 520se was only putting out 25-30w on 10, maybe 50 on 15m and 100 or so 20 thru 80. Also noticed max output on the 520 was not at the deepest dip in the plate current so I realized it's time to go thru the 520, do an alignment and neutralize the finals. Possibly the 6146's are starting to get a tad soft so I'll find that out when I do the alignment. This is an old rig but in nice condition. So that brings me to the question.......is there maintenance that an amp requires periodically (like alignment on an old hf rig) to get it up to snuff? (other than tube replacement and/or cleaning)
The "someone" scenario just irks me as Ive seen it happen way too many times, to others and myself. Yours just caught me at a bad time and sorry I reacted that way. Yep In your amp for sure. Besides your not understanding thermal dynamics which was covered yesterday in Post 14 that is the poorest designed amp Ive ever seen for air flow and the RF circuit also promotes instability. The external fan is another example of the help that amp needs. When it sold here it was a 1000W INPUT amp, not 1200W as in the manual and even at 600W out it was marginal. And since the UK rules say 400W PEP why are you even discussing this?? Many complain about the Dentron Clipperton L but even at 2000W Input it is a better designed amp than the Yaesu family and its known flaws are easily correctable.
Nope. But check the 12BY7A driver tube in the TS-520 also...when that tube starts to go soft it produces similar symptoms to the final tubes getting soft.
I agree the driver is the first to go. "Dropped pretty hard on 10 (below 200w) " If you are reading close to 200 watts out on a 520SE, I would test into a dummy load. And buy a better meter, Not just use the internal one, If it says 200 Watts out on any band. That radio would have to be FM if it does 200 out. Maybe that radio has the FM mod ?
