Hello Andrea -
Here is the link to the review with the 480V voltage measurements
of the FL-50:
http://home.alphalink.com.au/~gfs/yaesu/Yeasu7.htm
Page one of the review says the rated voltage is 500V.
(500V at 100mA for 50w input). This would provide
a reasonable 250V buss for the low level stages.

D8 and D9 of the FL-50B are connected as for a voltage doubler.
If this were a standard full wave supply,
with half DC voltage taken from the transformer center tap,
they would not be present.

You might look at the label on multi-section capacitor C81 itself,
perhaps there is an error on the schematic which shows only 350V
for that first section.

73,
Ed Knobloch


Andrea Baldoni wrote:
Heriberto wrote:

: I not have FT-50, but I have FT-200 with 6JS6 (x2) tubes in
: amplifier outpout.- The plate voltage can be around 700 to 800 volt. , not
: 350.- It is a cause yoir problem off low power.- The idle plate current can
: be 50 or 60 ma.

Thankyou Heriberto and Edward, but I have the schematics and I confirm that
the 350V are ok. It comes from a 120 0 120 transformer rectified in full
bridge. 240*1.41 ~ 340V. The capacitor is rated 350V so it's the right
voltage. The center tap of the transformer is used to have ~ 170V to ground
for the plate of other tubes, by sharing two of the 4 diodes of the bridge
for 340V.
I never see such configuration... curious method for saving components
Anyway, that voltage is also ok, measured only +160V, but with all tubes
working.

Yes, 6JS6C could be used to 1000V, if I recall correctly, it's used such
way in a old yaesu 1000W linear amplifier, in a quartet.
But theoretically, also with +350V (say, 200VRMS) and a 125mA measured
current, the power should be at least 30W. In reality, despite the theory,
the measured RMS voltage over the cap while transmitting is more like
100V than 200, so no power.

Ciao,
AB