On Sun, 04 Jan 2004 23:42:21 GMT, "author" wrote:

The power supply in my radio has audible hum in the background
and bypassing the diode rectifiers with capacitors does not eliminate the
hum. There is no hum when using battery power. The solution is to
build my own power supply. Does anyone have a design for a compact 6V
supply that I could build for this purpose?

Do you mean the dc output was bypassed i.e. capacitors were
paralleled with the dc output? Bypassing rectifiers will
increase or create hum. I would suggest replace all the
rectifiers (could be leaky) and capacitors (could be leaky too)
first. One can add too much capacitance too by the way. They
become the load instead of the actual load. What is the voltage
and current requirement and the actual under load? That too can
be the source of hum.

"Frank Dresser" ) writes:
"Gray Shockley" wrote in message
.com...
On Tue, 6 Jan 2004 19:44:01 -0600, Charles Hawtrey wrote


I'm in the middle of slightly rebuilding a couple of old radios and I
need a
very few parts (our only electronics store is gone because of the
health of
the owner [sigh].


What are y'all's recommendations for a component mail order house?

I'm specifically looking for one where there won't be a $15 shipping
charge
on five dollars worth of parts.

As always/Thank you very much.



Gray Shockley

Here's a few places I've done business with:

http://www.danssmallpartsandkits.net/

Dan has great prices and usually has a good turnaround time. I've been
100% satisfied. However, it's a one man operation, and there have been
times when he's been so backlogged that there have been newsgroup
threads wondering if Dan is still in business or even still alive.

One advantage (or disadvantage) of him is that he's focused on radio
related parts, and mainly long standard common items. So he's not
a good place to get the latest widget, and he is lacking in some things
that would be nice to order from him (such as a better selection of IF
filters), but for projects using common items you should be able to
get all the parts from him. You can get the semiconductors, the bypass
capacitors, the variable capacitors and the toroids. I'm not sure
a place like Digikey or Mouser carry toroids or variable capacitors (if
they do the latter, likely the prices would be high) so ordering elsewhere
might require multiple orders.

Michael

"H. Dziardziel" wrote:

On Sun, 04 Jan 2004 23:42:21 GMT, "author" wrote:

The power supply in my radio has audible hum in the background
and bypassing the diode rectifiers with capacitors does not eliminate the
hum. There is no hum when using battery power. The solution is to
build my own power supply. Does anyone have a design for a compact 6V
supply that I could build for this purpose?

Do you mean the dc output was bypassed i.e. capacitors were
paralleled with the dc output? Bypassing rectifiers will
increase or create hum. I would suggest replace all the
rectifiers (could be leaky) and capacitors (could be leaky too)
first. One can add too much capacitance too by the way. They
become the load instead of the actual load. What is the voltage
and current requirement and the actual under load? That too can
be the source of hum.

The purpose of bypassing (in parallel) the power supply diodes
(rectifiers) with capacitors (.010-mfd) is to remove RF switching
transients (caused by the diodes) from the DC output. This can often
eliminate the kind of hum which is heard when the radio is tuned to a
strong station but the hum goes away when the volume is turned down all
the way. Regular AC hum caused by a problem with the power supply filter
capacitor(s) can still be heard when the volume is down.


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In article , "starman"
wrote:

The purpose of bypassing (in parallel) the power supply diodes
(rectifiers) with capacitors (.010-mfd) is to remove RF switching
transients (caused by the diodes) from the DC output. This can often
eliminate the kind of hum which is heard when the radio is tuned to a
strong station but the hum goes away when the volume is turned down all
the way. Regular AC hum caused by a problem with the power supply filter
capacitor(s) can still be heard when the volume is down.

There's a third pssibility: the hum may be coming from the AC line itself
(as 60 or 120 Hz modulated RF in common mode). The design of the power
supply has little influence on this. Common mode chokes are sometimes
helpful, but not terribly effective. Measures to reduce common mode
coupling to the receiver's antenna input (balanced antenna, grounded coax
feed) are more effective in this case.

--
| John Doty "You can't confuse me, that's my job."
| Home:
| Work:

On Thu, 08 Jan 2004 00:02:45 -0500, starman
wrote:



The purpose of bypassing (in parallel) the power supply diodes
(rectifiers) with capacitors (.010-mfd) is to remove RF switching
transients (caused by the diodes) from the DC output. This can often
eliminate the kind of hum which is heard when the radio is tuned to a
strong station but the hum goes away when the volume is turned down all
the way. Regular AC hum caused by a problem with the power supply filter
capacitor(s) can still be heard when the volume is down.



Hmmnnn...no pun intended of course....
http://home.computer.net/~pritch/shortwav.htm
This occurred to me too but if in fact the diodes were bypassed
and there was no effect I dismissed that source -- too quickly on
second thought, thanks.