I have a Heathkit SB-102 that I have used for a couple of years primarly on
CW, but I had wanted to use it some on SSB. On CW it puts out a good solid
100Watts.. But on SSB it only puts out about 10W unless I whistly loudly
into the mic. I tested the tubes on a tester, not sure if it works or
not, but they appeared to be good.. and i've replaced all of the
resistors I could see that might have lost value over the years. Anyone
have specific experience with a SB-102 and the SSB audio input going soft ?



--
Registered Linux User #346565

On CW it puts out a good solid
100Watts.. But on SSB it only puts out about 10W unless I whistly loudly
into the mic.

Jeremy-

I had two SB-102s and an HW-100 about 25 years ago. Neither had low audio,
although there were numerous other problems.

From the wording of your message, I assume the radio did have good audio, but
now doesn't, using the same microphone et cetera. As with most tube rigs, the
first thing to do was to check the tubes. Your tester would probably have
shown up a problem that would have caused your low audio, even if it wasn't a
conductance-type tester.

The microphone must be high impedance. If you are using a low impedance
microphone, you just might not have noticed the low output before.

Is the microphone from Heath? They supplied a hand microphone with a high
impedance ceramic element, similar to the Turner 350-C. If you happen to have
a non-Heath microphone with a crystal element, it is possible the element is
going bad. A Rochelle Salts crystal element must be kept at just the right
humidity level. If it gets too humid, the crystal absorbs moisture and
dissolves. If it gets to dry, its "waters of crystalization" evaporate and the
crystal turns to powder!

When you replaced resistors, did you refer to the manual for the correct value?
Some of the old resistors can be misread. Mistaking red or yellow for orange
in the third band, would make a ten-fold error.

Beyond tubes, microphones and resistors, there may be an electrolytic capacitor
that has either developed leakage or has dried out. Most of the lower value
capacitors are probably OK, but no guarantee.

If you have the manual, there are probably voltages marked on the circuit
diagram. It might help isolate the problem if you checked them with a high
impedance meter.

73 & Good Luck
Fred, K4DII

On CW it puts out a good solid
100Watts.. But on SSB it only puts out about 10W unless I whistly loudly
into the mic.

Jeremy-

I had two SB-102s and an HW-100 about 25 years ago. Neither had low audio,
although there were numerous other problems.

From the wording of your message, I assume the radio did have good audio, but
now doesn't, using the same microphone et cetera. As with most tube rigs, the
first thing to do was to check the tubes. Your tester would probably have
shown up a problem that would have caused your low audio, even if it wasn't a
conductance-type tester.

The microphone must be high impedance. If you are using a low impedance
microphone, you just might not have noticed the low output before.

Is the microphone from Heath? They supplied a hand microphone with a high
impedance ceramic element, similar to the Turner 350-C. If you happen to have
a non-Heath microphone with a crystal element, it is possible the element is
going bad. A Rochelle Salts crystal element must be kept at just the right
humidity level. If it gets too humid, the crystal absorbs moisture and
dissolves. If it gets to dry, its "waters of crystalization" evaporate and the
crystal turns to powder!

When you replaced resistors, did you refer to the manual for the correct value?
Some of the old resistors can be misread. Mistaking red or yellow for orange
in the third band, would make a ten-fold error.

Beyond tubes, microphones and resistors, there may be an electrolytic capacitor
that has either developed leakage or has dried out. Most of the lower value
capacitors are probably OK, but no guarantee.

If you have the manual, there are probably voltages marked on the circuit
diagram. It might help isolate the problem if you checked them with a high
impedance meter.

73 & Good Luck
Fred, K4DII

Fred McKenzie wrote:

On CW it puts out a good solid
100Watts.. But on SSB it only puts out about 10W unless I whistly loudly
into the mic.

Jeremy-

I had two SB-102s and an HW-100 about 25 years ago. Neither had low
audio,
although there were numerous other problems.

From the wording of your message, I assume the radio did have good audio,
but
now doesn't, using the same microphone et cetera. As with most tube rigs,
the
first thing to do was to check the tubes. Your tester would probably have
shown up a problem that would have caused your low audio, even if it
wasn't a
conductance-type tester.

The microphone must be high impedance. If you are using a low impedance
microphone, you just might not have noticed the low output before.

Is the microphone from Heath? They supplied a hand microphone with a high
impedance ceramic element, similar to the Turner 350-C. If you happen to
have
a non-Heath microphone with a crystal element, it is possible the element
is
going bad. A Rochelle Salts crystal element must be kept at just the
right
humidity level. If it gets too humid, the crystal absorbs moisture and
dissolves. If it gets to dry, its "waters of crystalization" evaporate
and the
crystal turns to powder!

When you replaced resistors, did you refer to the manual for the correct
value?
Some of the old resistors can be misread. Mistaking red or yellow for
orange
in the third band, would make a ten-fold error.

Beyond tubes, microphones and resistors, there may be an electrolytic
capacitor
that has either developed leakage or has dried out. Most of the lower
value
capacitors are probably OK, but no guarantee.

If you have the manual, there are probably voltages marked on the circuit
diagram. It might help isolate the problem if you checked them with a
high
impedance meter.

73 & Good Luck
Fred, K4DII

Yes, I referred to the manual for the values of the resisters. To explain.
When i upgraded to General in 1997 or 1998, a friend donated the radio to
me in "non-working" condition.. and another friend fixed it. In his fixing
of the radio he said all he had to do was replace some resisters and it
started working nicely.

Upon closer inspection he didn't replace the resisters but he patched them.
As in he added a resister in parallel to the existing resister to get it to
the resistance it was supposed to be instead of removing it and putting in
a totally new one. What I did was take both out and put in a totally new
one on all of them i could find.

As far as i know the entier time i had the rig it was low on output on SSB,
but i didn't notice until i had had the rig for a year since i was a
tech-plus and used the rig only on CW.

First off I tryed the stock heathkit mic that i believe came with the radio
and it was even worse, it would barely put our 5 - 8 watts. I found a high
impedance amplified microphone that i wired up and hooked up to the radio,
which then got its output up to around 10 watts.. with peaks if i whistle
into it loudly. I read the manual and attempted to match the impedance of
the mics to what the rig wanted.

The capacitors is something i never thought about until i was reading your
message. I've restored a old AM broadcast band radio once and I had to
replace all the capacitors, but I never thought about it on the SB-102.




--
Registered Linux User #346565
WA5K

Fred McKenzie wrote:

On CW it puts out a good solid
100Watts.. But on SSB it only puts out about 10W unless I whistly loudly
into the mic.

Jeremy-

I had two SB-102s and an HW-100 about 25 years ago. Neither had low
audio,
although there were numerous other problems.

From the wording of your message, I assume the radio did have good audio,
but
now doesn't, using the same microphone et cetera. As with most tube rigs,
the
first thing to do was to check the tubes. Your tester would probably have
shown up a problem that would have caused your low audio, even if it
wasn't a
conductance-type tester.

The microphone must be high impedance. If you are using a low impedance
microphone, you just might not have noticed the low output before.

Is the microphone from Heath? They supplied a hand microphone with a high
impedance ceramic element, similar to the Turner 350-C. If you happen to
have
a non-Heath microphone with a crystal element, it is possible the element
is
going bad. A Rochelle Salts crystal element must be kept at just the
right
humidity level. If it gets too humid, the crystal absorbs moisture and
dissolves. If it gets to dry, its "waters of crystalization" evaporate
and the
crystal turns to powder!

When you replaced resistors, did you refer to the manual for the correct
value?
Some of the old resistors can be misread. Mistaking red or yellow for
orange
in the third band, would make a ten-fold error.

Beyond tubes, microphones and resistors, there may be an electrolytic
capacitor
that has either developed leakage or has dried out. Most of the lower
value
capacitors are probably OK, but no guarantee.

If you have the manual, there are probably voltages marked on the circuit
diagram. It might help isolate the problem if you checked them with a
high
impedance meter.

73 & Good Luck
Fred, K4DII

Yes, I referred to the manual for the values of the resisters. To explain.
When i upgraded to General in 1997 or 1998, a friend donated the radio to
me in "non-working" condition.. and another friend fixed it. In his fixing
of the radio he said all he had to do was replace some resisters and it
started working nicely.

Upon closer inspection he didn't replace the resisters but he patched them.
As in he added a resister in parallel to the existing resister to get it to
the resistance it was supposed to be instead of removing it and putting in
a totally new one. What I did was take both out and put in a totally new
one on all of them i could find.

As far as i know the entier time i had the rig it was low on output on SSB,
but i didn't notice until i had had the rig for a year since i was a
tech-plus and used the rig only on CW.

First off I tryed the stock heathkit mic that i believe came with the radio
and it was even worse, it would barely put our 5 - 8 watts. I found a high
impedance amplified microphone that i wired up and hooked up to the radio,
which then got its output up to around 10 watts.. with peaks if i whistle
into it loudly. I read the manual and attempted to match the impedance of
the mics to what the rig wanted.

The capacitors is something i never thought about until i was reading your
message. I've restored a old AM broadcast band radio once and I had to
replace all the capacitors, but I never thought about it on the SB-102.




--
Registered Linux User #346565
WA5K

Jeremy Salch ) writes:
Fred McKenzie wrote:

On CW it puts out a good solid
100Watts.. But on SSB it only puts out about 10W unless I whistly loudly
into the mic.

Jeremy-

I had two SB-102s and an HW-100 about 25 years ago. Neither had low
audio,
although there were numerous other problems.

From the wording of your message, I assume the radio did have good audio,
but
now doesn't, using the same microphone et cetera. As with most tube rigs,
the
first thing to do was to check the tubes. Your tester would probably have
shown up a problem that would have caused your low audio, even if it
wasn't a
conductance-type tester.

The microphone must be high impedance. If you are using a low impedance
microphone, you just might not have noticed the low output before.

Is the microphone from Heath? They supplied a hand microphone with a high
impedance ceramic element, similar to the Turner 350-C. If you happen to
have
a non-Heath microphone with a crystal element, it is possible the element
is
going bad. A Rochelle Salts crystal element must be kept at just the
right
humidity level. If it gets too humid, the crystal absorbs moisture and
dissolves. If it gets to dry, its "waters of crystalization" evaporate
and the
crystal turns to powder!

When you replaced resistors, did you refer to the manual for the correct
value?
Some of the old resistors can be misread. Mistaking red or yellow for
orange
in the third band, would make a ten-fold error.

Beyond tubes, microphones and resistors, there may be an electrolytic
capacitor
that has either developed leakage or has dried out. Most of the lower
value
capacitors are probably OK, but no guarantee.

If you have the manual, there are probably voltages marked on the circuit
diagram. It might help isolate the problem if you checked them with a
high
impedance meter.

73 & Good Luck
Fred, K4DII

Yes, I referred to the manual for the values of the resisters. To explain.
When i upgraded to General in 1997 or 1998, a friend donated the radio to
me in "non-working" condition.. and another friend fixed it. In his fixing
of the radio he said all he had to do was replace some resisters and it
started working nicely.

Upon closer inspection he didn't replace the resisters but he patched them.
As in he added a resister in parallel to the existing resister to get it to
the resistance it was supposed to be instead of removing it and putting in
a totally new one. What I did was take both out and put in a totally new
one on all of them i could find.

As far as i know the entier time i had the rig it was low on output on SSB,
but i didn't notice until i had had the rig for a year since i was a
tech-plus and used the rig only on CW.

First off I tryed the stock heathkit mic that i believe came with the radio
and it was even worse, it would barely put our 5 - 8 watts. I found a high
impedance amplified microphone that i wired up and hooked up to the radio,
which then got its output up to around 10 watts.. with peaks if i whistle
into it loudly. I read the manual and attempted to match the impedance of
the mics to what the rig wanted.

The capacitors is something i never thought about until i was reading your
message. I've restored a old AM broadcast band radio once and I had to
replace all the capacitors, but I never thought about it on the SB-102.

But you need to look at what's different when the rig moves from CW
to SSB.

There are a number of methods that are used to generate CW in an SSB
rig, and how it's done will help to isolate the problem. You can
feed an audio tone into the AF amplifier feeding the balanced modulator,
and there there is very little different. You can unbalanced the
balanced modulator. You can feed the carrier oscillator around the
balanced modulator, and maybe someties it's even fed around the IF
filter. I have no idea which scheme is used in your rig.

The audio tone method would suggest the microphone, or something
in the first audio stage or so (depending on where the audio tone
is injected). It can't be the balanced modulator, or anything that comes
later.

Unbalancing the balanced modulator would suggest the problem lies
in the stage or stages between the mic jack and the balanced modulator,
unless the microphone is faulty. The balanced modulator should be fine,
as well as anything that comes later.

Feeding the carrier oscillator around the balanced modulator, and
I'm not sure how common this scheme was, would leave the problem with
those audio stages or the balanced modulator.

If you had an audio generator of some kind, you could try applying
it right where the audio goes into the balanced modulator. I'm not
sure what audo voltage level should be there, but if you applied
that same audio voltage and you get full power, you know the
problem lies before that. Then you move the AF generator
a stage closer to the mic jack, and see if there's a drop-off
in power output (one is expecting that you have a dummy load
on the output for this testing). Then move the AF generator
to the mic jack and see if there's a drop-off.

At some point as you move towards the mic jack, there will be
a drop-off, and that will be the stage that needs work. Maybe
the tube, maybe a resistor, or maybe a coupling capacitor or
bypass capacitor.

If you still get a low output with the signal generator
feeding into the balanced modulator, then the problem lies
in the balanced modulator.

Or, the IF filter has gone bad (not likely, and you should
notice a deterioration on receive), or the carrier oscillator
is not on frequency. Again, I'm not sure of the rig's
scheme, but the carrier oscillator crystal may be changed
when going to CW. It's possible the SSB crystal is off frequency,
and so the IF filter isn't passing the signal properly. Scratch
that, since you'd be noticing a problem in receive. Feed
the AF generator into the balanced modulator, and vary it's
frequency to see if the output changes significantly as
the audio frequency changes.

The problem can be broken down, but one has to start by
looking at the schematic to see what could
be the problem.

Michael VE2BVW

Jeremy Salch ) writes:
Fred McKenzie wrote:

On CW it puts out a good solid
100Watts.. But on SSB it only puts out about 10W unless I whistly loudly
into the mic.

Jeremy-

I had two SB-102s and an HW-100 about 25 years ago. Neither had low
audio,
although there were numerous other problems.

From the wording of your message, I assume the radio did have good audio,
but
now doesn't, using the same microphone et cetera. As with most tube rigs,
the
first thing to do was to check the tubes. Your tester would probably have
shown up a problem that would have caused your low audio, even if it
wasn't a
conductance-type tester.

The microphone must be high impedance. If you are using a low impedance
microphone, you just might not have noticed the low output before.

Is the microphone from Heath? They supplied a hand microphone with a high
impedance ceramic element, similar to the Turner 350-C. If you happen to
have
a non-Heath microphone with a crystal element, it is possible the element
is
going bad. A Rochelle Salts crystal element must be kept at just the
right
humidity level. If it gets too humid, the crystal absorbs moisture and
dissolves. If it gets to dry, its "waters of crystalization" evaporate
and the
crystal turns to powder!

When you replaced resistors, did you refer to the manual for the correct
value?
Some of the old resistors can be misread. Mistaking red or yellow for
orange
in the third band, would make a ten-fold error.

Beyond tubes, microphones and resistors, there may be an electrolytic
capacitor
that has either developed leakage or has dried out. Most of the lower
value
capacitors are probably OK, but no guarantee.

If you have the manual, there are probably voltages marked on the circuit
diagram. It might help isolate the problem if you checked them with a
high
impedance meter.

73 & Good Luck
Fred, K4DII

Yes, I referred to the manual for the values of the resisters. To explain.
When i upgraded to General in 1997 or 1998, a friend donated the radio to
me in "non-working" condition.. and another friend fixed it. In his fixing
of the radio he said all he had to do was replace some resisters and it
started working nicely.

Upon closer inspection he didn't replace the resisters but he patched them.
As in he added a resister in parallel to the existing resister to get it to
the resistance it was supposed to be instead of removing it and putting in
a totally new one. What I did was take both out and put in a totally new
one on all of them i could find.

As far as i know the entier time i had the rig it was low on output on SSB,
but i didn't notice until i had had the rig for a year since i was a
tech-plus and used the rig only on CW.

First off I tryed the stock heathkit mic that i believe came with the radio
and it was even worse, it would barely put our 5 - 8 watts. I found a high
impedance amplified microphone that i wired up and hooked up to the radio,
which then got its output up to around 10 watts.. with peaks if i whistle
into it loudly. I read the manual and attempted to match the impedance of
the mics to what the rig wanted.

The capacitors is something i never thought about until i was reading your
message. I've restored a old AM broadcast band radio once and I had to
replace all the capacitors, but I never thought about it on the SB-102.

But you need to look at what's different when the rig moves from CW
to SSB.

There are a number of methods that are used to generate CW in an SSB
rig, and how it's done will help to isolate the problem. You can
feed an audio tone into the AF amplifier feeding the balanced modulator,
and there there is very little different. You can unbalanced the
balanced modulator. You can feed the carrier oscillator around the
balanced modulator, and maybe someties it's even fed around the IF
filter. I have no idea which scheme is used in your rig.

The audio tone method would suggest the microphone, or something
in the first audio stage or so (depending on where the audio tone
is injected). It can't be the balanced modulator, or anything that comes
later.

Unbalancing the balanced modulator would suggest the problem lies
in the stage or stages between the mic jack and the balanced modulator,
unless the microphone is faulty. The balanced modulator should be fine,
as well as anything that comes later.

Feeding the carrier oscillator around the balanced modulator, and
I'm not sure how common this scheme was, would leave the problem with
those audio stages or the balanced modulator.

If you had an audio generator of some kind, you could try applying
it right where the audio goes into the balanced modulator. I'm not
sure what audo voltage level should be there, but if you applied
that same audio voltage and you get full power, you know the
problem lies before that. Then you move the AF generator
a stage closer to the mic jack, and see if there's a drop-off
in power output (one is expecting that you have a dummy load
on the output for this testing). Then move the AF generator
to the mic jack and see if there's a drop-off.

At some point as you move towards the mic jack, there will be
a drop-off, and that will be the stage that needs work. Maybe
the tube, maybe a resistor, or maybe a coupling capacitor or
bypass capacitor.

If you still get a low output with the signal generator
feeding into the balanced modulator, then the problem lies
in the balanced modulator.

Or, the IF filter has gone bad (not likely, and you should
notice a deterioration on receive), or the carrier oscillator
is not on frequency. Again, I'm not sure of the rig's
scheme, but the carrier oscillator crystal may be changed
when going to CW. It's possible the SSB crystal is off frequency,
and so the IF filter isn't passing the signal properly. Scratch
that, since you'd be noticing a problem in receive. Feed
the AF generator into the balanced modulator, and vary it's
frequency to see if the output changes significantly as
the audio frequency changes.

The problem can be broken down, but one has to start by
looking at the schematic to see what could
be the problem.

Michael VE2BVW

The capacitors is something i never thought about until i was reading your
message. I've restored a old AM broadcast band radio once and I had to
replace all the capacitors, but I never thought about it on the SB-102.

Jeremy-

I've been through that with old radios as well. Back in the late 50s or early
60s, there was a major improvement in capacitor construction. They introduced
a layer of plastic film (mylar?) with the paper, and drasticaly reduced leakage
as the capacitor aged. That is why I wouldn't just replace capacitors without
some other symptom.

Another thing to check, is whether the microphone amplifier tube is the correct
one. If a 12AU7 had been installed in place of a 12AX7, the gain would be
somewhat lower, but the tube might check 100%.

73, Fred, K4DII

The capacitors is something i never thought about until i was reading your
message. I've restored a old AM broadcast band radio once and I had to
replace all the capacitors, but I never thought about it on the SB-102.

Jeremy-

I've been through that with old radios as well. Back in the late 50s or early
60s, there was a major improvement in capacitor construction. They introduced
a layer of plastic film (mylar?) with the paper, and drasticaly reduced leakage
as the capacitor aged. That is why I wouldn't just replace capacitors without
some other symptom.

Another thing to check, is whether the microphone amplifier tube is the correct
one. If a 12AU7 had been installed in place of a 12AX7, the gain would be
somewhat lower, but the tube might check 100%.

73, Fred, K4DII

Michael Black wrote:
Jeremy Salch ) writes:

Fred McKenzie wrote:


On CW it puts out a good solid
100Watts.. But on SSB it only puts out about 10W unless I whistly loudly
into the mic.

Jeremy-

I had two SB-102s and an HW-100 about 25 years ago. Neither had low

audio,

although there were numerous other problems.

From the wording of your message, I assume the radio did have good audio,

but

now doesn't, using the same microphone et cetera. As with most tube rigs,

the

first thing to do was to check the tubes. Your tester would probably have
shown up a problem that would have caused your low audio, even if it

wasn't a

conductance-type tester.

The microphone must be high impedance. If you are using a low impedance
microphone, you just might not have noticed the low output before.

Is the microphone from Heath? They supplied a hand microphone with a high
impedance ceramic element, similar to the Turner 350-C. If you happen to

have

a non-Heath microphone with a crystal element, it is possible the element

is

going bad. A Rochelle Salts crystal element must be kept at just the

right

humidity level. If it gets too humid, the crystal absorbs moisture and
dissolves. If it gets to dry, its "waters of crystalization" evaporate

and the

crystal turns to powder!

When you replaced resistors, did you refer to the manual for the correct

value?

Some of the old resistors can be misread. Mistaking red or yellow for

orange

in the third band, would make a ten-fold error.

Beyond tubes, microphones and resistors, there may be an electrolytic

capacitor

that has either developed leakage or has dried out. Most of the lower

value

capacitors are probably OK, but no guarantee.

If you have the manual, there are probably voltages marked on the circuit
diagram. It might help isolate the problem if you checked them with a

high

impedance meter.

73 & Good Luck
Fred, K4DII

Yes, I referred to the manual for the values of the resisters. To explain.
When i upgraded to General in 1997 or 1998, a friend donated the radio to
me in "non-working" condition.. and another friend fixed it. In his fixing
of the radio he said all he had to do was replace some resisters and it
started working nicely.

Upon closer inspection he didn't replace the resisters but he patched them.
As in he added a resister in parallel to the existing resister to get it to
the resistance it was supposed to be instead of removing it and putting in
a totally new one. What I did was take both out and put in a totally new
one on all of them i could find.

As far as i know the entier time i had the rig it was low on output on SSB,
but i didn't notice until i had had the rig for a year since i was a
tech-plus and used the rig only on CW.

First off I tryed the stock heathkit mic that i believe came with the radio
and it was even worse, it would barely put our 5 - 8 watts. I found a high
impedance amplified microphone that i wired up and hooked up to the radio,
which then got its output up to around 10 watts.. with peaks if i whistle
into it loudly. I read the manual and attempted to match the impedance of
the mics to what the rig wanted.

The capacitors is something i never thought about until i was reading your
message. I've restored a old AM broadcast band radio once and I had to
replace all the capacitors, but I never thought about it on the SB-102.


But you need to look at what's different when the rig moves from CW
to SSB.

There are a number of methods that are used to generate CW in an SSB
rig, and how it's done will help to isolate the problem. You can
feed an audio tone into the AF amplifier feeding the balanced modulator,
and there there is very little different. You can unbalanced the
balanced modulator. You can feed the carrier oscillator around the
balanced modulator, and maybe someties it's even fed around the IF
filter. I have no idea which scheme is used in your rig.

The audio tone method would suggest the microphone, or something
in the first audio stage or so (depending on where the audio tone
is injected). It can't be the balanced modulator, or anything that comes
later.

Unbalancing the balanced modulator would suggest the problem lies
in the stage or stages between the mic jack and the balanced modulator,
unless the microphone is faulty. The balanced modulator should be fine,
as well as anything that comes later.

Feeding the carrier oscillator around the balanced modulator, and
I'm not sure how common this scheme was, would leave the problem with
those audio stages or the balanced modulator.

If you had an audio generator of some kind, you could try applying
it right where the audio goes into the balanced modulator. I'm not
sure what audo voltage level should be there, but if you applied
that same audio voltage and you get full power, you know the
problem lies before that. Then you move the AF generator
a stage closer to the mic jack, and see if there's a drop-off
in power output (one is expecting that you have a dummy load
on the output for this testing). Then move the AF generator
to the mic jack and see if there's a drop-off.

At some point as you move towards the mic jack, there will be
a drop-off, and that will be the stage that needs work. Maybe
the tube, maybe a resistor, or maybe a coupling capacitor or
bypass capacitor.

If you still get a low output with the signal generator
feeding into the balanced modulator, then the problem lies
in the balanced modulator.

Or, the IF filter has gone bad (not likely, and you should
notice a deterioration on receive), or the carrier oscillator
is not on frequency. Again, I'm not sure of the rig's
scheme, but the carrier oscillator crystal may be changed
when going to CW. It's possible the SSB crystal is off frequency,
and so the IF filter isn't passing the signal properly. Scratch
that, since you'd be noticing a problem in receive. Feed
the AF generator into the balanced modulator, and vary it's
frequency to see if the output changes significantly as
the audio frequency changes.

The problem can be broken down, but one has to start by
looking at the schematic to see what could
be the problem.

Michael VE2BVW

Let me add one other possibility based on experience with an old SB110

which I think uses similar circuitry. I was using the rig in a VHF
contest
and not getting through to a station about 200 miles away that I
normally worked easily. Switched to CW and got a 599 and that made me
realize the SSB output was down. I went through the same reasoning that
it must be something that was different in SSB mode. However the
problem turned out to be the tuning in an IF stage; it had drifted far
enough off resonance to drop the drive way down. However in CW the
unbalanced balanced modulator normally produced much more drive than
mike audio so it made up for the mistuned stage. With the stage
retuned, SSB was now full power and the drive control had to be reduced
for CW use. Bottom line - it is worth checking the tuning on each of
the IF stages.
73, John