One of your 6146B tubes may be gassy. Remove one tube completely
(don't just lift the plate connector), key the rig with no drive
and check that you have 20mA plate current with the remaining tube.
Add drive, tune and load for 125mA with the single tube,
and see if you still get 50W output. Repeat tests with other tube.

If the tubes are balanced, each will draw 20mA quiescent current
with the same setting of final bias adjustment.

73,
Ed Knobloch K4PF

Angel Vilaseca wrote:
When trying to tune the final amp on my Kenwood TS-820, I get little or no
plate dip.
The amp can be tuned though, but I only get 50 W HF out, instead of 100 W.
Plate current is nominal at 250 mA and 800 V on the 6146B anodes.

I made these measurements with the rig connected to a 50 ohms dummy load
and the HF output was confirmed with a HP 432A power mwter.

So I get 50 W HF out for 200 W DC in. Efficiency is terrible at only 25%.
All the missing HF power must be dissipated in the anodes because they glow
red after a few seconds.

The same thing happens on all bands. Sometimes, when trying to tune on 7
MHz, plate current gets higher than 350 mA and the rig fuse blows.

I suspect there must be something wrong in the tank circuit.

Upon visual inspection, nothing looks charred in there. No arcing noises.

I checked the plate capacitor, which is OK. I unsoldered it and measured it
@ .001 uF, as it should be.

So I am wondering where to look next. Any ideas?

many tnx in advance

Angel Vilaseca HB9SLV