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

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:
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

Mark Rehorst wrote:
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?

If it is a buzz, it is probably not a cap. If it is a hum, it is probably
a cap. What stage is the buzz from? If you pull the mixer tube, does it
still buzz? If you pull the IF stages? What if you pull the detector?
At what stage is the buzz getting into the signal?

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

Cain Electronics in Hampton, VA still has TV tuning sets.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Mark Rehorst wrote:
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?

If it is a buzz, it is probably not a cap. If it is a hum, it is probably
a cap. What stage is the buzz from? If you pull the mixer tube, does it
still buzz? If you pull the IF stages? What if you pull the detector?
At what stage is the buzz getting into the signal?

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

Cain Electronics in Hampton, VA still has TV tuning sets.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

I tried adding caps across the rectifiers- no good.
I tried bypassing the main filter cap with a 20nf ceramic cap. No
good.
I tried swapping out the rectifiers. No good.
I added a 3 terminal voltage regulator, reducing the audio amp supply
voltage to about 10V. Buzz all but gone. I have to press my ear to
the speaker to hear any buzz now.

The distortion in the audio seems to have gone up a bit, so maybe an
amp that can operate from a lower voltage would be better. I'll look
into audio amp chips and see if I can find a suitable device.

Thanks for all input.

MR

Mark Rehorst wrote:

I added a 3 terminal voltage regulator, reducing the audio amp supply
voltage to about 10V. Buzz all but gone. I have to press my ear to
the speaker to hear any buzz now.

The distortion in the audio seems to have gone up a bit, so maybe an
amp that can operate from a lower voltage would be better.

Killing the audio amp is a very effective way of eliminating all sorts
of QRM/QRN. Just kidding, good luck with it.

-Bill

Mark Rehorst wrote:

I added a 3 terminal voltage regulator, reducing the audio amp supply
voltage to about 10V. Buzz all but gone. I have to press my ear to
the speaker to hear any buzz now.

The distortion in the audio seems to have gone up a bit, so maybe an
amp that can operate from a lower voltage would be better.

Killing the audio amp is a very effective way of eliminating all sorts
of QRM/QRN. Just kidding, good luck with it.

-Bill

Mark Rehorst wrote:
I tried adding caps across the rectifiers- no good.
I tried bypassing the main filter cap with a 20nf ceramic cap. No
good.
I tried swapping out the rectifiers. No good.
I added a 3 terminal voltage regulator, reducing the audio amp supply
voltage to about 10V. Buzz all but gone. I have to press my ear to
the speaker to hear any buzz now.

Try replacing that one cap with a larger valued cap. Or make a pi filter
with a resistor and another cap.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

I tried adding caps across the rectifiers- no good.
I tried bypassing the main filter cap with a 20nf ceramic cap. No
good.
I tried swapping out the rectifiers. No good.
I added a 3 terminal voltage regulator, reducing the audio amp supply
voltage to about 10V. Buzz all but gone. I have to press my ear to
the speaker to hear any buzz now.

The distortion in the audio seems to have gone up a bit, so maybe an
amp that can operate from a lower voltage would be better. I'll look
into audio amp chips and see if I can find a suitable device.

Thanks for all input.

MR