In article , Chuck Harris
writes:

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.

Right, and I am amazed that the top-of-line Heathkit AR-15 FM receiver used a
ratio detector. Supposedly they can sound just as good, but I've always
associated ratio dets with "cheap." --Mike K.

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In article , (Scott Dorsey)
writes:

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.


OK, so it was arcing internally, and getting ready to let smoke out, in great
puffs :-)

I have a cheap AM/FM clock radio that sounds like light-dimmer power line
noise
even on FM.

It has a vacuum fluorescent display, doesn't it? Disconnect the display
and it'll be quiet.

Kinda spoils the fun of a clock radio, especially when the radio sux but the
clock is very reliable (keeps perfect time during power outages).
Seriously, this is a big red LED display. The vacuum flourescent jobs are
actually electron tubes, were used back in late '70s on clocks and Gottlieb
pinball machines.

Most good SW portable radios do have s wticht to kill the digital readout,
though -- good idea. --Mike K.


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In article , (Scott Dorsey)
writes:

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.


OK, so it was arcing internally, and getting ready to let smoke out, in great
puffs :-)

I have a cheap AM/FM clock radio that sounds like light-dimmer power line
noise
even on FM.

It has a vacuum fluorescent display, doesn't it? Disconnect the display
and it'll be quiet.

Kinda spoils the fun of a clock radio, especially when the radio sux but the
clock is very reliable (keeps perfect time during power outages).
Seriously, this is a big red LED display. The vacuum flourescent jobs are
actually electron tubes, were used back in late '70s on clocks and Gottlieb
pinball machines.

Most good SW portable radios do have s wticht to kill the digital readout,
though -- good idea. --Mike K.


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Mike Knudsen wrote:


2) switch to fast recovery diodes.


How would these be specified in a catalog? "Fast recovery power diodes"?
Thanks, Mike K.

Yes. A number like 1N5407 rings a bell but I'm saying that on memory.
Actually I've never seen a case where the diodes caused any audible
noise in a regular ole radio although I hear this recommendation often.
Tunable hum at times maybe.

If this set is making a racket like powerline noise as opposed to a 60
cycle hum it pretty much has to be some leakage in the AC
components...plug, switch, xfmr, etc.

Remotely possible is some sort of weird rf oscillation. Should be easy
to sort between the two by powering it up on DC.

-BM

Mike Knudsen wrote:


2) switch to fast recovery diodes.


How would these be specified in a catalog? "Fast recovery power diodes"?
Thanks, Mike K.

Yes. A number like 1N5407 rings a bell but I'm saying that on memory.
Actually I've never seen a case where the diodes caused any audible
noise in a regular ole radio although I hear this recommendation often.
Tunable hum at times maybe.

If this set is making a racket like powerline noise as opposed to a 60
cycle hum it pretty much has to be some leakage in the AC
components...plug, switch, xfmr, etc.

Remotely possible is some sort of weird rf oscillation. Should be easy
to sort between the two by powering it up on DC.

-BM

Moonman wrote:
In article , (Scott Dorsey)
wrote:


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."



Can someone please, please explain to me what you're talking about here. Of
course I know that IF cans have holes in the top through which to turn the
ferrite slugs inside to screw them up or down for tuning purposes. What I
don't know is where to get the tuning wands for old radios (or even if they
are any different from those for new radios, like I presume I might buy at
Radio ****). I also don't know why when the query is made about finding
tuning tools for "IF can slugs" (obviously talking about radios), the
response is the contact an outfit that "still has *TV* tuning sets". I'm
about to start working on three old ('30s and '40s) radios that I bought on
eBay, and I don't have ANY tuning slugs. I also have some old boatanchors
to work on. Where should I get my set of tuning tools?
A somewhat ignorant person

Most alignment tool sets will have a variety of sizes
included...everything from the tiny hex common in later vintage oriental
gear to the larger hex size found in older equipment. The alignment
tool set at RS has (had) 6 or so double-ended tools.
If none are found, Antique Electronic Supply has a wide variety of them
in sets and single. http://www.tubesandmore.com

-Bill

Moonman wrote:
In article , (Scott Dorsey)
wrote:


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."



Can someone please, please explain to me what you're talking about here. Of
course I know that IF cans have holes in the top through which to turn the
ferrite slugs inside to screw them up or down for tuning purposes. What I
don't know is where to get the tuning wands for old radios (or even if they
are any different from those for new radios, like I presume I might buy at
Radio ****). I also don't know why when the query is made about finding
tuning tools for "IF can slugs" (obviously talking about radios), the
response is the contact an outfit that "still has *TV* tuning sets". I'm
about to start working on three old ('30s and '40s) radios that I bought on
eBay, and I don't have ANY tuning slugs. I also have some old boatanchors
to work on. Where should I get my set of tuning tools?
A somewhat ignorant person

Most alignment tool sets will have a variety of sizes
included...everything from the tiny hex common in later vintage oriental
gear to the larger hex size found in older equipment. The alignment
tool set at RS has (had) 6 or so double-ended tools.
If none are found, Antique Electronic Supply has a wide variety of them
in sets and single. http://www.tubesandmore.com

-Bill

Hi Mike,

I was posting that reply to the side topic of the cheapy
AM/FM that buzzed like a bee.

I don't have a schematic or other info on the SX190. Is is
vacuum tube rectifiers, or selenium?

If it is selenium, they tend to get noisy when they go bad. It could
be they are arcing internally (or breaking over) when they are under
the stress of the peak inverse voltage.

-Chuck, WA3UQV


Mike Knudsen wrote:
In article , Chuck Harris
writes:


A lot of that kind of noise comes from solid state rectifiers in the
powersupply.


But why would the SX-190 suddenly develop this problem, unless it's something
else? --Mike K.

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

Hi Mike,

I was posting that reply to the side topic of the cheapy
AM/FM that buzzed like a bee.

I don't have a schematic or other info on the SX190. Is is
vacuum tube rectifiers, or selenium?

If it is selenium, they tend to get noisy when they go bad. It could
be they are arcing internally (or breaking over) when they are under
the stress of the peak inverse voltage.

-Chuck, WA3UQV


Mike Knudsen wrote:
In article , Chuck Harris
writes:


A lot of that kind of noise comes from solid state rectifiers in the
powersupply.


But why would the SX-190 suddenly develop this problem, unless it's something
else? --Mike K.

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

For fast recovery diodes and bridges, look in your mouser catalog under
rectron, or ST. They both make gobs and gobs of the beasts.

If the unit was ok, and now suddenly buzzes, it might mean that the
bridge has one diode that is breaking down. First try replacing the
bridge with most anything silicon with at least 2x the HV as a PIV.

If that doesn't work, then look at the cap that goes from the power line
to the chassis. These are supposed to keep power line noise out of
the insides of the chassis. They also take a beating, and are usually
cheap wax paper caps.

Another thing you can do is run the antenna of another radio as a coax
and a 1-2 inch loop of a few turns. bring this loop around to various
parts of the SX, and listen for the noise. If your SX can hear it,
another receiver should also.

-Chuck

Mike Knudsen wrote:
In article , Chuck Harris
writes:


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!)


Would shunt caps help? What if it's a bridge unit and I can't get in series?
Replace with discrete diodes and Rs?


2) switch to fast recovery diodes.


How would these be specified in a catalog? "Fast recovery power diodes"?
Thanks, Mike K.



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