Kaito KA-2100 upgrade
 

The built in AC power supply on this radio has quite a bit of switching
noise. Each of the diodes are bypassed, but they neglected to bypass the
secondary of the power transformer.
Place a 1uF ceramic cap across the secondary (input to the diode rectifiers)
and this will eliminate that "light dimmer" type of buzz on the MW band.

Pete

Kaito KA-2100 upgrade
 

On Aug 24, 4:11*am, "Pete KE9OA" wrote:
The built in AC power supply on this radio has quite a bit of switching
noise. Each of the diodes are bypassed, but they neglected to bypass the
secondary of the power transformer.
Place a 1uF ceramic cap across the secondary (input to the diode rectifiers)
and this will eliminate that "light dimmer" type of buzz on the MW band.

Pete

Nice work Pete - that mains connection sure is a pest on MW.
Wish I lived near you to send it for that upgrade (unfortunately if I
try it I will ruin the radio and burn the house down)

JP

Kaito KA-2100 upgrade
 

On Aug 24, 4:15*pm, "Pete KE9OA" wrote:
I understand John.................actually, the power supply/regulator board
is a separate board that is held down with three small screws. The secondary
of the power transformer connects to two large pads on the board. The 1uF
100V non polarized cap can be soldered on the underside of the board.
Normally, the power supply diodes have a radiated power density that decays
pretty quickly above 600kHz or so. The manufacturer must have been using
some pretty fast switching diodes when they built this radio. The difference
after the mod is day and night.......it is as if a switch was turned off on
the interfering source.
When I had the radio open, I took a look at the loopstick antenna. It
appears to be the same type of twin coil ferrite that is used in the CCRadio
Shortwave. One of these days, I will dismantle it further and see if there
are any alignment points for the MW range. My unit droops in sensitivity
below 540kHz. This is typical of many radios when the loopstick is aligned
at 600kHz for the low end of the band. I also noticed this with the Sony
6800W.
If you could find a tech in your area, that person would be able to do the
power supply mod in about 10 minutes. If you need any more details, feel
free to e-mail me anytime at


Pete

Thanks so much Pete, that's really useful and kind of you. I do have a
local ham in the village that is as good as an Olympic swordsman with
a soldering iron, so I shall go and ask him.

BTW that "The 1uF 100V non polarized cap"
that you mention - my set is a RP2100 from China with 240v AC mains,
does that alter the value?

best of 73's
JP in Montagu South Africa

Kaito KA-2100 upgrade
 

I understand John.................actually, the power supply/regulator board
is a separate board that is held down with three small screws. The secondary
of the power transformer connects to two large pads on the board. The 1uF
100V non polarized cap can be soldered on the underside of the board.
Normally, the power supply diodes have a radiated power density that decays
pretty quickly above 600kHz or so. The manufacturer must have been using
some pretty fast switching diodes when they built this radio. The difference
after the mod is day and night.......it is as if a switch was turned off on
the interfering source.
When I had the radio open, I took a look at the loopstick antenna. It
appears to be the same type of twin coil ferrite that is used in the CCRadio
Shortwave. One of these days, I will dismantle it further and see if there
are any alignment points for the MW range. My unit droops in sensitivity
below 540kHz. This is typical of many radios when the loopstick is aligned
at 600kHz for the low end of the band. I also noticed this with the Sony
6800W.
If you could find a tech in your area, that person would be able to do the
power supply mod in about 10 minutes. If you need any more details, feel
free to e-mail me anytime at


Pete

wrote in message
...
On Aug 24, 4:11 am, "Pete KE9OA" wrote:
The built in AC power supply on this radio has quite a bit of switching
noise. Each of the diodes are bypassed, but they neglected to bypass the
secondary of the power transformer.
Place a 1uF ceramic cap across the secondary (input to the diode
rectifiers)
and this will eliminate that "light dimmer" type of buzz on the MW band.

Pete

Nice work Pete - that mains connection sure is a pest on MW.
Wish I lived near you to send it for that upgrade (unfortunately if I
try it I will ruin the radio and burn the house down)

JP

Kaito KA-2100 upgrade
 

Hi John,

A 100V cap should be fine. A mylar, polyester, ceramic, or any other film
type should be ok. I modified a friend's old Radio Shack TRF radio many
years ago with this same mod; this way, the low end of the MW band was
useful. Let me know if you have any problem getting ahold of the part.

Pete

wrote in message
...
On Aug 24, 4:15 pm, "Pete KE9OA" wrote:
I understand John.................actually, the power supply/regulator
board
is a separate board that is held down with three small screws. The
secondary
of the power transformer connects to two large pads on the board. The 1uF
100V non polarized cap can be soldered on the underside of the board.
Normally, the power supply diodes have a radiated power density that
decays
pretty quickly above 600kHz or so. The manufacturer must have been using
some pretty fast switching diodes when they built this radio. The
difference
after the mod is day and night.......it is as if a switch was turned off
on
the interfering source.
When I had the radio open, I took a look at the loopstick antenna. It
appears to be the same type of twin coil ferrite that is used in the
CCRadio
Shortwave. One of these days, I will dismantle it further and see if there
are any alignment points for the MW range. My unit droops in sensitivity
below 540kHz. This is typical of many radios when the loopstick is aligned
at 600kHz for the low end of the band. I also noticed this with the Sony
6800W.
If you could find a tech in your area, that person would be able to do the
power supply mod in about 10 minutes. If you need any more details, feel
free to e-mail me anytime at


Pete

Thanks so much Pete, that's really useful and kind of you. I do have a
local ham in the village that is as good as an Olympic swordsman with
a soldering iron, so I shall go and ask him.

BTW that "The 1uF 100V non polarized cap"
that you mention - my set is a RP2100 from China with 240v AC mains,
does that alter the value?

best of 73's
JP in Montagu South Africa

Kaito KA-2100 upgrade
 

wrote in message
...
BTW that "The 1uF 100V non polarized cap"
that you mention - my set is a RP2100 from China with 240v AC mains,
does that alter the value?


No, in power supplies the transformer secondary is the low voltage side.

Kaito KA-2100 upgrade
 

As long as you use a cap that has twice the peak to peak rating of the
voltage at the secondary, you are fine. Since this is a 9V regulated supply
with a 3-pin regulator, I would expect at least 12VAC at the transformer
output. Multiply that by 2.828, double it again, and you have the required
voltage for the cap to be within its safe operating area. A 100V cap is fine
in this case.
As this poster mentioned, the primary voltage isn't the determining factor,
but the secondary voltage is the one you want to look at. Make sure you use
either a ceramic or film cap. A non-polarized electrolytic cap wouldn't be
suitable.

Pete

"bw" wrote in message
...

wrote in message
...
BTW that "The 1uF 100V non polarized cap"
that you mention - my set is a RP2100 from China with 240v AC mains,
does that alter the value?


No, in power supplies the transformer secondary is the low voltage side.