Help... SB-200 behaving badly
 

Okay, all you linear amplifier experts...
put yer thinking caps on...

I have a Heath SB-200 amp that's behaving badly.
It works just fine on 80m through 15m, putting
out over 750 Watts PEP on 80m and 600 Watts PEP
on 15m. On 10m, it's not working right at all.
Instead of the plate current dipping at maximum
output, it's peaking at maximum output, and it's
very low when off resonance. This is just the
opposite of what I'd expect, and of what happens
on the other four bands. Maximum output on 10m
is only about 150 Watts PEP, with 100 Watts of
drive. There are no signs of arcing going on.
This amp lived a questionable life before I got
it, which made me think that perhaps the PA tank
coil had been hacked for 11m use. Nope, it's
fine. The band switch contacts are in fine shape
as well. I've rebuilt the entire RF deck, so all
of the wiring is correct and the soldering is
professional-grade. The circuitry is all stock
and completely matches the original schematic.
Since each band has its own input tank circuit,
is it possible that I have a bad component in the
10m input tank circuit that's hosing things up?

Thanks in advance for any help you can provide!

73,
Dean K5DH

I have a Heath SB-200 amp that's behaving badly.
It works just fine on 80m through 15m, putting
out over 750 Watts PEP on 80m and 600 Watts PEP
on 15m. On 10m, it's not working right at all.
Instead of the plate current dipping at maximum
output, it's peaking at maximum output, and it's
very low when off resonance. This is just the
opposite of what I'd expect, and of what happens
on the other four bands. Maximum output on 10m
is only about 150 Watts PEP, with 100 Watts of

While probably not the problem, some later modle Heathkit amps were made so
they would not operate on 10 meters. You have to change some wiring around
the input tuned circuits or filtering. Not sure exectlly what, but a friend
of mine had to do this and he was telling me about it. All that junk about
not making amps that would work in and around the CB frequencies.

I have a Heath SB-200 amp that's behaving badly.
It works just fine on 80m through 15m, putting
out over 750 Watts PEP on 80m and 600 Watts PEP
on 15m. On 10m, it's not working right at all.
Instead of the plate current dipping at maximum
output, it's peaking at maximum output, and it's
very low when off resonance. This is just the
opposite of what I'd expect, and of what happens
on the other four bands. Maximum output on 10m
is only about 150 Watts PEP, with 100 Watts of

While probably not the problem, some later modle Heathkit amps were made so
they would not operate on 10 meters. You have to change some wiring around
the input tuned circuits or filtering. Not sure exectlly what, but a friend
of mine had to do this and he was telling me about it. All that junk about
not making amps that would work in and around the CB frequencies.

On Wed, 10 Dec 2003 19:46:33 -0500, "Ralph Mowery"
wrote:


I have a Heath SB-200 amp that's behaving badly.
It works just fine on 80m through 15m, putting
out over 750 Watts PEP on 80m and 600 Watts PEP
on 15m. On 10m, it's not working right at all.
Instead of the plate current dipping at maximum
output, it's peaking at maximum output, and it's
very low when off resonance. This is just the
opposite of what I'd expect, and of what happens
on the other four bands. Maximum output on 10m
is only about 150 Watts PEP, with 100 Watts of

While probably not the problem, some later modle Heathkit amps were made so
they would not operate on 10 meters. You have to change some wiring around
the input tuned circuits or filtering.

I seem to recall it was around '78 or '79 when they stopped selling
amps that were 10 meters capable, right out of the box.

Bob
k5qwg

Not sure exectlly what, but a friend
of mine had to do this and he was telling me about it. All that junk about
not making amps that would work in and around the CB frequencies.

On Wed, 10 Dec 2003 19:46:33 -0500, "Ralph Mowery"
wrote:


I have a Heath SB-200 amp that's behaving badly.
It works just fine on 80m through 15m, putting
out over 750 Watts PEP on 80m and 600 Watts PEP
on 15m. On 10m, it's not working right at all.
Instead of the plate current dipping at maximum
output, it's peaking at maximum output, and it's
very low when off resonance. This is just the
opposite of what I'd expect, and of what happens
on the other four bands. Maximum output on 10m
is only about 150 Watts PEP, with 100 Watts of

While probably not the problem, some later modle Heathkit amps were made so
they would not operate on 10 meters. You have to change some wiring around
the input tuned circuits or filtering.

I seem to recall it was around '78 or '79 when they stopped selling
amps that were 10 meters capable, right out of the box.

Bob
k5qwg

Not sure exectlly what, but a friend
of mine had to do this and he was telling me about it. All that junk about
not making amps that would work in and around the CB frequencies.

On 10-Dec-2003, (K5DH) wrote:

on 15m. On 10m, it's not working right at all.
Instead of the plate current dipping at maximum
output, it's peaking at maximum output, and it's
very low when off resonance. This is just the

That sounds like what happens with parasitic oscillation. Maybe the neutralization?? needs fixing
or adjustment.

Ken Fowler, KO6NO

On 10-Dec-2003, (K5DH) wrote:

on 15m. On 10m, it's not working right at all.
Instead of the plate current dipping at maximum
output, it's peaking at maximum output, and it's
very low when off resonance. This is just the

That sounds like what happens with parasitic oscillation. Maybe the neutralization?? needs fixing
or adjustment.

Ken Fowler, KO6NO

"Ralph Mowery" wrote in message
...

I have a Heath SB-200 amp that's behaving badly.
It works just fine on 80m through 15m, putting
out over 750 Watts PEP on 80m and 600 Watts PEP
on 15m. On 10m, it's not working right at all.
Instead of the plate current dipping at maximum
output, it's peaking at maximum output, and it's
very low when off resonance. This is just the
opposite of what I'd expect, and of what happens
on the other four bands. Maximum output on 10m
is only about 150 Watts PEP, with 100 Watts of

While probably not the problem, some later modle Heathkit amps were made
so
they would not operate on 10 meters. You have to change some wiring
around
the input tuned circuits or filtering. Not sure exectlly what, but a
friend
of mine had to do this and he was telling me about it. All that junk
about
not making amps that would work in and around the CB frequencies.



He said he had a SB-200, which by definition is 80-10. A SB-221 did not
operate on ten.

It is possible you are not tuning it correctly. On ten meters, things can
become quite 'squirly'. Put it into a good dummy load and experiment a bit.
Try reducing the load. Bring it up slow. Go between load and plate, see
how that goes.

Dan/W4NTI

"Ralph Mowery" wrote in message
...

I have a Heath SB-200 amp that's behaving badly.
It works just fine on 80m through 15m, putting
out over 750 Watts PEP on 80m and 600 Watts PEP
on 15m. On 10m, it's not working right at all.
Instead of the plate current dipping at maximum
output, it's peaking at maximum output, and it's
very low when off resonance. This is just the
opposite of what I'd expect, and of what happens
on the other four bands. Maximum output on 10m
is only about 150 Watts PEP, with 100 Watts of

While probably not the problem, some later modle Heathkit amps were made
so
they would not operate on 10 meters. You have to change some wiring
around
the input tuned circuits or filtering. Not sure exectlly what, but a
friend
of mine had to do this and he was telling me about it. All that junk
about
not making amps that would work in and around the CB frequencies.



He said he had a SB-200, which by definition is 80-10. A SB-221 did not
operate on ten.

It is possible you are not tuning it correctly. On ten meters, things can
become quite 'squirly'. Put it into a good dummy load and experiment a bit.
Try reducing the load. Bring it up slow. Go between load and plate, see
how that goes.

Dan/W4NTI

Possibly it's not neutralised correctly?

Cheers.
Murray vk4aok

Dan/W4NTI wrote:

"Ralph Mowery" wrote in message
...

I have a Heath SB-200 amp that's behaving badly.
It works just fine on 80m through 15m, putting
out over 750 Watts PEP on 80m and 600 Watts PEP
on 15m. On 10m, it's not working right at all.
Instead of the plate current dipping at maximum
output, it's peaking at maximum output, and it's
very low when off resonance. This is just the
opposite of what I'd expect, and of what happens
on the other four bands. Maximum output on 10m
is only about 150 Watts PEP, with 100 Watts of

While probably not the problem, some later modle Heathkit amps were made
so
they would not operate on 10 meters. You have to change some wiring
around
the input tuned circuits or filtering. Not sure exectlly what, but a
friend
of mine had to do this and he was telling me about it. All that junk
about
not making amps that would work in and around the CB frequencies.



He said he had a SB-200, which by definition is 80-10. A SB-221 did not
operate on ten.

It is possible you are not tuning it correctly. On ten meters, things can
become quite 'squirly'. Put it into a good dummy load and experiment a bit.
Try reducing the load. Bring it up slow. Go between load and plate, see
how that goes.

Dan/W4NTI