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

Edward Knobloch wrote:

: 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.

Thankyou for made me note this. I saw that page many times without never
noting the voltage chart. Hovewer, it's for the 50 and not 50B, even if
they have probably mostly the same circuit.

: 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.

In full wave rectifiers with center tap, we have only two diodes BUT the gnd
is in the center tap. Well, you could use the center as GND and have a
positive supply from the diodes, or also the opposite (inverted): put
diodes on GND and have the center tap at positive. So, with a 120 0 120
transformer, we have a +120V (*1.41).
If we ignore the center tap, we need 4 diodes to have a full
bridge and the transformer is like a 0 240, so +240V.
In that schematic, we have the two cases superimposed at the same time:
the center tap is not connected to GND at all, instead is used to form
another supply, the +160. It is a (inverted) full wave
rectifier with center tap and two diodes, D8 and D9. The +350 is a 4 diode
bridge, reusing D8 and D9 again but ignoring the center tap.

As I stated, I never see that way before, but do you agree with my analysis?

: 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.

I'll look and report. Anyway, I suppose the problem is not there.

Ciao,
AB

Hi, Andrea

Yes, you are right! Sorry about the confusion here.

It sounds like your rig should only make 10W at that low plate voltage.
It could be that they reduced the power of the original FL-50
to 10W in the FL-50B for use by the Japanese "fourth class amateur radio
operator", who did not need to pass a telegraphy examination.
This was easily done by reducing the plate voltage through a change
in power supply transformer.

73,
Ed



Andrea Baldoni wrote:
Edward Knobloch wrote:

: 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.

Thankyou for made me note this. I saw that page many times without never
noting the voltage chart. Hovewer, it's for the 50 and not 50B, even if
they have probably mostly the same circuit.

: 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.

In full wave rectifiers with center tap, we have only two diodes BUT the gnd
is in the center tap. Well, you could use the center as GND and have a
positive supply from the diodes, or also the opposite (inverted): put
diodes on GND and have the center tap at positive. So, with a 120 0 120
transformer, we have a +120V (*1.41).
If we ignore the center tap, we need 4 diodes to have a full
bridge and the transformer is like a 0 240, so +240V.
In that schematic, we have the two cases superimposed at the same time:
the center tap is not connected to GND at all, instead is used to form
another supply, the +160. It is a (inverted) full wave
rectifier with center tap and two diodes, D8 and D9. The +350 is a 4 diode
bridge, reusing D8 and D9 again but ignoring the center tap.

As I stated, I never see that way before, but do you agree with my analysis?

: 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.

I'll look and report. Anyway, I suppose the problem is not there.

Ciao,
AB

Edward Knobloch wrote:

: It sounds like your rig should only make 10W at that low plate voltage.
: It could be that they reduced the power of the original FL-50
: to 10W in the FL-50B for use by the Japanese "fourth class amateur radio
: operator", who did not need to pass a telegraphy examination.

I heard of the power reduced versions in the australian site (about the
FL-10/40), but elsewere (rigpix database for instance) it's indicated as a
75W input. Now I'm sending mail to everyone I could find in Internet that
seems to have a FL-50B. Who has used it, must know at least the power
output! Hope someone will reply.

Anyway, if that's the case, it's a good and a bad news at the same time: I
worked for almost a week in troubleshooting a perfectly working transmitter,
I bought some spare tubes and a tube checker, etc...
But I discovered again the vacuum tube world so much in this week!
....that I decided to seek more old radio and I posted an announce for
buying an Hallicrafters SX-88 and/or a SX-28!!!

And again, I got acquainted with this newsgroup

Ciao,
AB

Edward Knobloch wrote:

: It sounds like your rig should only make 10W at that low plate voltage.
: It could be that they reduced the power of the original FL-50

New informations.
I had been able to receive a response from a FL-50B owner. He told me
he no more has any manual, but the output power should be 30/40W.
Hovewer, his transmitter, bought used from a CB, never output more than 15W,
also after realignment and changing final tube.
Wherever the problem is, it seems to be a common problem. I promised to
told him how to fix it, if I'll ever be able to fix mine...

How should be the output impedance of the 6JS6C? I'm beginning to suspect
it's not correctly loaded...

Ciao,
AB