My SX-190 has buzzed at a level just loud enough to be annoying since
I got it a couple years ago (minus a lot of time when it wasn't
working at all) even in standby. One of the things I did to the radio
is replace the electrolytic caps, including the main power supply
filter. I used the same 2200 uF the schematic called for, but the
buzz is still there. Does anyone with one of these radios have a real
quiet set, or do they all buzz like this? Would putting caps across
the rectifiers reduce the buzz, or do I need to go to a quieter
external supply? Or should I do something to the audio amp?

One more thing- where can I get a set of tuning tools that includes
the hex drivers for IF can slugs?

Thanks,

MR

P.S. Download 100+ pages of SX/AX-190 documentation in an indexed .pdf
file he
http://www.rehorst.com/mrehorst/Alli...Info-Oct02.pdf

Mark Rehorst wrote:
My SX-190 has buzzed at a level just loud enough to be annoying

quiet set, or do they all buzz like this? Would putting caps across
the rectifiers reduce the buzz, or do I need to go to a quieter
external supply? Or should I do something to the audio amp?


I had a buzzy set of that vintage, not an SX-190, and it turned out the
power xfmr was bad. Sounded just like power line noise and was worse
with an external antenna. Go figure.

One more thing- where can I get a set of tuning tools that includes
the hex drivers for IF can slugs?

Radio Shack?

-Bill

On Fri, 31 Oct 2003 00:00:33 -0400, --exray-- wrote:

I had a buzzy set of that vintage, not an SX-190, and it turned out the
power xfmr was bad. Sounded just like power line noise and was worse
with an external antenna. Go figure.

Was that mechanical buzzing of the transformer, or was there some
electrical problem? My radio buzzes through the speaker.

One more thing- where can I get a set of tuning tools that includes
the hex drivers for IF can slugs?

Radio Shack?

Really? I'll check it out. Thanks!

-Bill

Mark Rehorst wrote:
On Fri, 31 Oct 2003 00:00:33 -0400, --exray-- wrote:


I had a buzzy set of that vintage, not an SX-190, and it turned out the
power xfmr was bad. Sounded just like power line noise and was worse
with an external antenna. Go figure.


Was that mechanical buzzing of the transformer, or was there some
electrical problem? My radio buzzes through the speaker.

No, this was electrical buzzing just like receiving power line noise.
mechanically it was quiet.

-Bill

In article , --exray-- writes:

Was that mechanical buzzing of the transformer, or was there some
electrical problem? My radio buzzes through the speaker.

No, this was electrical buzzing just like receiving power line noise.
mechanically it was quiet.

Any idea of what was wrong with the power trans inside, or did you just replace
it and throw it away? Maybe the shielding between the windings was kaput.

I have a cheap AM/FM clock radio that sounds like light-dimmer power line noise
even on FM. I've tried tacking caps all over the place, to no effect. The DC
supply is clean on a scope. You have to wonder how such a sound gets into FM
-- it sounds exactly like the sort of noise that sends you reching for the ANL
switch on a real radio. --Mike K.

Oscar loves trash, but hates Spam! Delete him to reply to me.

Mike Knudsen wrote:

I have a cheap AM/FM clock radio that sounds like light-dimmer power line noise
even on FM. I've tried tacking caps all over the place, to no effect. The DC
supply is clean on a scope. You have to wonder how such a sound gets into FM
-- it sounds exactly like the sort of noise that sends you reching for the ANL
switch on a real radio. --Mike K.


A lot of that kind of noise comes from solid state rectifiers in the
powersupply. The HV rectifiers don't switch off quickly enough, and
essentially short out the supply for an instant around the zero crossing
point of the input sinewave. This always sounds like a very raucus
60Hz (half wave rect.), or 120Hz (full wave rect.) buzz, and it comes in
thru some RF or IF stage in the receiver.

This can be solved one of two ways:

1) add a series resistor to each each diode to limit how much current
can flow, 100 ohms, or some such. (Note, one for each diode!)

2) switch to fast recovery diodes.


As to why cheapy FM radios respond to this kind of AM noise, it is all
in the use of a ratio detector vs a limiter/discriminator. Ratio
detectors are pretty good at eliminating AM, but limiter/discriminator
stages are very good at eliminating AM. Ratio detectors are basically
simpler, and as such much cheaper.

-Chuck Harris, WA3UQV

Mike Knudsen wrote:

I have a cheap AM/FM clock radio that sounds like light-dimmer power line noise
even on FM. I've tried tacking caps all over the place, to no effect. The DC
supply is clean on a scope. You have to wonder how such a sound gets into FM
-- it sounds exactly like the sort of noise that sends you reching for the ANL
switch on a real radio. --Mike K.


A lot of that kind of noise comes from solid state rectifiers in the
powersupply. The HV rectifiers don't switch off quickly enough, and
essentially short out the supply for an instant around the zero crossing
point of the input sinewave. This always sounds like a very raucus
60Hz (half wave rect.), or 120Hz (full wave rect.) buzz, and it comes in
thru some RF or IF stage in the receiver.

This can be solved one of two ways:

1) add a series resistor to each each diode to limit how much current
can flow, 100 ohms, or some such. (Note, one for each diode!)

2) switch to fast recovery diodes.


As to why cheapy FM radios respond to this kind of AM noise, it is all
in the use of a ratio detector vs a limiter/discriminator. Ratio
detectors are pretty good at eliminating AM, but limiter/discriminator
stages are very good at eliminating AM. Ratio detectors are basically
simpler, and as such much cheaper.

-Chuck Harris, WA3UQV

Mike Knudsen wrote:
In article , --exray-- writes:

Was that mechanical buzzing of the transformer, or was there some
electrical problem? My radio buzzes through the speaker.

No, this was electrical buzzing just like receiving power line noise.
mechanically it was quiet.

Any idea of what was wrong with the power trans inside, or did you just replace
it and throw it away? Maybe the shielding between the windings was kaput.

Insulation breakdown.

I have a cheap AM/FM clock radio that sounds like light-dimmer power line noise
even on FM. I've tried tacking caps all over the place, to no effect. The DC
supply is clean on a scope. You have to wonder how such a sound gets into FM
-- it sounds exactly like the sort of noise that sends you reching for the ANL
switch on a real radio. --Mike K.

It has a vacuum fluorescent display, doesn't it? Disconnect the display
and it'll be quiet.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Mike Knudsen wrote:
In article , --exray-- writes:

Was that mechanical buzzing of the transformer, or was there some
electrical problem? My radio buzzes through the speaker.

No, this was electrical buzzing just like receiving power line noise.
mechanically it was quiet.

Any idea of what was wrong with the power trans inside, or did you just replace
it and throw it away? Maybe the shielding between the windings was kaput.

Insulation breakdown.

I have a cheap AM/FM clock radio that sounds like light-dimmer power line noise
even on FM. I've tried tacking caps all over the place, to no effect. The DC
supply is clean on a scope. You have to wonder how such a sound gets into FM
-- it sounds exactly like the sort of noise that sends you reching for the ANL
switch on a real radio. --Mike K.

It has a vacuum fluorescent display, doesn't it? Disconnect the display
and it'll be quiet.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In article , --exray-- writes:

Was that mechanical buzzing of the transformer, or was there some
electrical problem? My radio buzzes through the speaker.

No, this was electrical buzzing just like receiving power line noise.
mechanically it was quiet.

Any idea of what was wrong with the power trans inside, or did you just replace
it and throw it away? Maybe the shielding between the windings was kaput.

I have a cheap AM/FM clock radio that sounds like light-dimmer power line noise
even on FM. I've tried tacking caps all over the place, to no effect. The DC
supply is clean on a scope. You have to wonder how such a sound gets into FM
-- it sounds exactly like the sort of noise that sends you reching for the ANL
switch on a real radio. --Mike K.

Oscar loves trash, but hates Spam! Delete him to reply to me.