Hello!
I'm trying to repair a Sommerkamp(Yaesu) FL-50B. It does power up and transmit
but the output power is just 13W. I tried to replace final 6JS6C without any
adwantage, also replace the driver tube with same result.

The B+ is 350V, dropping to 325V while transmitting... Already tried to
exchange the plate voltage filter condenser, but apart slightly minor ripple,
no result in power output increase.

The transmitter is fully tuned, by me who may be not the best man for that,
but hovever, I have a good oscilloscope and anyway, the power output before
tuning was a (little little) less.

The antenna relay is ok. By measuring with oscilloscope the grid of the
6JS6C, I notice increasing in signal amplitude while rotating full scale
"carrier" control from 0 to 8. After 8, signal no more increase and there
is a little derive in 5.12.. Mhz carrier frequency. I think this is normal
for this kind of transmitter. The strange fact instead is that despite
driver signal is increasing, output power no further increase after carrier
control position 4.

I have regulated bias to 60mA, I suppose it's good for 6JS6C, I have not the
manual of the transmitter so I don't know exactly. Anyway, this has no
strong influence over power output. While at full power, I never see IC
more than 125mA, that's half the scale of the instrument. In PO measure,
it signs slightly more than .2

Well, no more. Someone who has more experience than me, please give me
his help!

....and also, I need to know what's (in Vpp) the right output of the carrier
quartz oscillator measured at the input of the balanced modulator.
While tuning, I forgot to record the previous amplitude... Now, if I recall
correctly, is 2.5Vpp... More than 3.5Vpp, the oscillator become unstable and
may not start oscillating, less than 2.5, output power further decrease...
So I may be right, but I would like to know if there is an exact value to
regulate on.

The power is more or less the same in every band, I use an FR-50B as VFO,
but with a 9MHZ quartz I have, the results are unchanged. All measure are
on a 50R dummy load with wattmeter. A Osker Block SWR/Wattmeter inserted
hovewer sign the same output and no SWR.

Ciao,
AB

I think I would be looking for a manual for it . The people that
designed it probably know more about it than anyone else.. HS
Andrea Baldoni wrote:
Hello!
I'm trying to repair a Sommerkamp(Yaesu) FL-50B. It does power up and transmit
but the output power is just 13W. I tried to replace final 6JS6C without any
adwantage, also replace the driver tube with same result.

The B+ is 350V, dropping to 325V while transmitting... Already tried to
exchange the plate voltage filter condenser, but apart slightly minor ripple,
no result in power output increase.

The transmitter is fully tuned, by me who may be not the best man for that,
but hovever, I have a good oscilloscope and anyway, the power output before
tuning was a (little little) less.

The antenna relay is ok. By measuring with oscilloscope the grid of the
6JS6C, I notice increasing in signal amplitude while rotating full scale
"carrier" control from 0 to 8. After 8, signal no more increase and there
is a little derive in 5.12.. Mhz carrier frequency. I think this is normal
for this kind of transmitter. The strange fact instead is that despite
driver signal is increasing, output power no further increase after carrier
control position 4.

I have regulated bias to 60mA, I suppose it's good for 6JS6C, I have not the
manual of the transmitter so I don't know exactly. Anyway, this has no
strong influence over power output. While at full power, I never see IC
more than 125mA, that's half the scale of the instrument. In PO measure,
it signs slightly more than .2

Well, no more. Someone who has more experience than me, please give me
his help!

...and also, I need to know what's (in Vpp) the right output of the carrier
quartz oscillator measured at the input of the balanced modulator.
While tuning, I forgot to record the previous amplitude... Now, if I recall
correctly, is 2.5Vpp... More than 3.5Vpp, the oscillator become unstable and
may not start oscillating, less than 2.5, output power further decrease...
So I may be right, but I would like to know if there is an exact value to
regulate on.

The power is more or less the same in every band, I use an FR-50B as VFO,
but with a 9MHZ quartz I have, the results are unchanged. All measure are
on a 50R dummy load with wattmeter. A Osker Block SWR/Wattmeter inserted
hovewer sign the same output and no SWR.

Ciao,
AB

Hi:
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.
I suspect that to his problem this in power supply.-

Regards
Heriberto
LU6DBU

escribió en el mensaje
oups.com...
I think I would be looking for a manual for it . The people that
designed it probably know more about it than anyone else.. HS
Andrea Baldoni wrote:
Hello!
I'm trying to repair a Sommerkamp(Yaesu) FL-50B. It does power up and
transmit
but the output power is just 13W. I tried to replace final 6JS6C without
any
adwantage, also replace the driver tube with same result.

The B+ is 350V, dropping to 325V while transmitting... Already tried to
exchange the plate voltage filter condenser, but apart slightly minor
ripple,
no result in power output increase.

The transmitter is fully tuned, by me who may be not the best man for
that,
but hovever, I have a good oscilloscope and anyway, the power output
before
tuning was a (little little) less.

The antenna relay is ok. By measuring with oscilloscope the grid of the
6JS6C, I notice increasing in signal amplitude while rotating full scale
"carrier" control from 0 to 8. After 8, signal no more increase and
there
is a little derive in 5.12.. Mhz carrier frequency. I think this is
normal
for this kind of transmitter. The strange fact instead is that despite
driver signal is increasing, output power no further increase after
carrier
control position 4.

I have regulated bias to 60mA, I suppose it's good for 6JS6C, I have not
the
manual of the transmitter so I don't know exactly. Anyway, this has no
strong influence over power output. While at full power, I never see IC
more than 125mA, that's half the scale of the instrument. In PO measure,
it signs slightly more than .2

Well, no more. Someone who has more experience than me, please give me
his help!

...and also, I need to know what's (in Vpp) the right output of the
carrier
quartz oscillator measured at the input of the balanced modulator.
While tuning, I forgot to record the previous amplitude... Now, if I
recall
correctly, is 2.5Vpp... More than 3.5Vpp, the oscillator become unstable
and
may not start oscillating, less than 2.5, output power further
decrease...
So I may be right, but I would like to know if there is an exact value
to
regulate on.

The power is more or less the same in every band, I use an FR-50B as
VFO,
but with a 9MHZ quartz I have, the results are unchanged. All measure
are
on a 50R dummy load with wattmeter. A Osker Block SWR/Wattmeter inserted
hovewer sign the same output and no SWR.

Ciao,
AB

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

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

wrote:

: I think I would be looking for a manual for it . The people that
: designed it probably know more about it than anyone else.. HS

Yes, I had looked in all internet sites, but no one seems to have that manual
scanned.
Anyway, I have the schematic.

If anyone out there has the manual and a scanner... I'll be happy to receive
it

Ciao,
AB

Hi,

It sounds like your High Voltage is quite low.
A review of the FL-50 says the HV is 480 VDC key open,
dropping to 440 VDC at c.w. full power output.
Look for a bad rectifier diode in the HV supply.

73,
Ed Knobloch

Andrea Baldoni wrote:
Hello!
I'm trying to repair a Sommerkamp(Yaesu) FL-50B. It does power up and transmit
but the output power is just 13W. I tried to replace final 6JS6C without any
adwantage, also replace the driver tube with same result.

The B+ is 350V, dropping to 325V while transmitting... Already tried to
exchange the plate voltage filter condenser, but apart slightly minor ripple,
no result in power output increase.

The transmitter is fully tuned, by me who may be not the best man for that,
but hovever, I have a good oscilloscope and anyway, the power output before
tuning was a (little little) less.

The antenna relay is ok. By measuring with oscilloscope the grid of the
6JS6C, I notice increasing in signal amplitude while rotating full scale
"carrier" control from 0 to 8. After 8, signal no more increase and there
is a little derive in 5.12.. Mhz carrier frequency. I think this is normal
for this kind of transmitter. The strange fact instead is that despite
driver signal is increasing, output power no further increase after carrier
control position 4.

I have regulated bias to 60mA, I suppose it's good for 6JS6C, I have not the
manual of the transmitter so I don't know exactly. Anyway, this has no
strong influence over power output. While at full power, I never see IC
more than 125mA, that's half the scale of the instrument. In PO measure,
it signs slightly more than .2

Well, no more. Someone who has more experience than me, please give me
his help!

...and also, I need to know what's (in Vpp) the right output of the carrier
quartz oscillator measured at the input of the balanced modulator.
While tuning, I forgot to record the previous amplitude... Now, if I recall
correctly, is 2.5Vpp... More than 3.5Vpp, the oscillator become unstable and
may not start oscillating, less than 2.5, output power further decrease...
So I may be right, but I would like to know if there is an exact value to
regulate on.

The power is more or less the same in every band, I use an FR-50B as VFO,
but with a 9MHZ quartz I have, the results are unchanged. All measure are
on a 50R dummy load with wattmeter. A Osker Block SWR/Wattmeter inserted
hovewer sign the same output and no SWR.

Ciao,
AB