Geoff/W5OMR wrote:
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
When you reduce the drive for AM operation you want to reduce the OUTPUT
to 1/4 power, not the input power. The input power will be somewhere
around 1/2 of full power when properly setup for AM.
73
Gary K4FMX
