> > When you tune up you tune it for max output at the 200 watt level with > > full drive. At that tune setting the tube will be around 60% efficient. > > Assuming Class C about 60 to 70% yes.
No. Class C is typically 70 to 75%. 60 to 65% is more likely for linear (AB1/AB2) operation. > I have run a P&H Linear amplifier at these levels and even the > 837s didn't glow red. But it may have been a little below 200 watts > carrier. I only had it for a few weeks so it would not be a fair test. > > Thanks for explaining it in more detail for me. > > I just remember QST articles where a single 811A was run at 200 > watts input as a linear amplifier or CW final and it did fine. The QST articles were probably talking about SSB or CW out of a single 811A at the 200w area. More than likely, it AM wasnn't considered in that test (*noting that QST is a publication of the ARRL, who would for a l-o-n-g time would NOT recognize AM as a valid mode of operation.) > Maybe it was more than 30% efficient... that part still mystifies me! > Sometimes I am dense though. Plate Voltage (Ep) * Plate Current (Ip) = DC Input. So, your quad 811A amp is running 1500v @ 400mA, you're running 600w DC input to the final. 150W per tube. That's to the max. When you tune the amp up for AM operation, leaving the amp at that -exact- tuning range, reduce the drive until you see only 150w, and probably a little less, to handle any asymmetry/transients in your voice*. 150W, modulated to 100% is around 600wPEP, but we're still talking DC INPUT, when you look at the 150W. So, 150 * 60% = around 90w of carrier output, which would be around 360W PEP output. Your mileage may vary, depending on Ep and Ip. If you just -have- to run a linear amplifier, instead of building up a plate modulated rig, at a MUCH higher efficiency rating, then build something with BIG tubes in it, that would handle the dissipation. like a pair of (or 3) 450TH's. 450W of plate dissipation, each. That'd bring you back up to the 1.5kW PEP level. That just might be a nice project... I could make a quad 450TL amp, and drive it with my Kenwood TS-680S I use mobile. (what a waste of a good tube!) 73 = Best Regards, -Geoff/W5OMR (*See: http://www.qsl.net/wa5bxo/asyam/aam3.html for more info on asymmetric voice patterns, and a few hams ideas for working WITH the 1500wPEP Output nonsensical FCC ruling.)
