ID an old part please

Archived from groups: rec.audio.tech (More info?)

ok wrote:
> In the AC input to a child's RCA record player. (model 6-emp-2b,
> couldn't find a schematic on line). It has 6, roughly 1/2" square
> plates, mounted perpendicularly on a tube with a small amount of space
> between each plate. It is painted a bright red- about an inch long.
> Selenium Rectifier? It measures 2Mohm one direction and 1Mohm the
> other. It has a screw which might be some type of adjustment or might
> just be a fastener to keep the assembly together.
> The unit motors and produces music at a whisper for 5 seconds and then
> a real loud hum makes you turn it off.
> Assuming the part is a rectifier can I replace it with a large diode?
> 5 amp? This thing has no transformer, one leg of the wall plug just
> goes through the mystery part into a cap can and runs the motor and a
> 25L6 tube. Music must have been an electrifying part of many peoples
> childhood in the two prong days. Thanks as always.


Sounds like a selenium rectifier, all right, but your problem is more likely
the capacitor.

Mark Z.

Archived from groups: rec.audio.tech (More info?)

ok wrote:
> In the AC input to a child's RCA record player. (model 6-emp-2b,
> couldn't find a schematic on line). It has 6, roughly 1/2" square
> plates, mounted perpendicularly on a tube with a small amount of
space
> between each plate. It is painted a bright red- about an inch long.
> Selenium Rectifier?

Sound like.

> It measures 2Mohm one direction and 1Mohm the other.

Problem is that these devices have fairly large forward voltage drops.
Ohmeters are not reliable indicators for devices like these.

If it's a typical record player, you could probably swap it out with a
IN4004 silicon rectifier to see if the rectifier is the problem.

> It has a screw which might be some type of adjustment or might
> just be a fastener to keep the assembly together.

The latter - just a fastener. Loosening it is a good way to make sure
the rectifier is bad for sure, unless the screw fits loosely in hole
in the rectifier stack.

Each fin on the rectifier stack represents a diode junction.

> The unit motors and produces music at a whisper for 5 seconds and
then
> a real loud hum makes you turn it off.

Sounds like there may be some bad power supply filter capacitor(s).

> Assuming the part is a rectifier can I replace it with a large
diode?

Yes, one capable of handling the power line voltage, IN4004 400 piv
silicon diode or equivalent.

> 5 amp?

Even 1/2 would be overkill. Its all about the voltage.

>This thing has no transformer, one leg of the wall plug just
> goes through the mystery part into a cap can and runs the motor and
a
> 25L6 tube.

Classic el-cheapo design from the 50s and 60s. Yes, its a silicon
rectifier, but the cap it runs into may very well be open.

> Music must have been an electrifying part of many peoples
> childhood in the two prong days.

Everything that conducted electricity was supposed to be insulated.
I've got my doubts about the tone arm wiring, though.

Archived from groups: rec.audio.tech (More info?)

You will have to change both the rectifier, and the main filter
capacitor(s). Take care that the polarization of these parts is important.

You can use a silicon diode equivalent to 1N4007 (very common rectifier) to
replace the selenium rectifier. Since the selenium rectifier normally goes
opened, you can put the silicon diode right across it. This way the old
diode becomes a terminal for the newer diode. The white band on the 1N4007
is the cathode side. The cathode side is the side that feeds to the + side
of the filter caps. The white band would be where the + side is on the old
diode.

To reduce the in-rush effect of the startup, you can put a 5 Watt resistor
of about 22 to 27 ohms in series with the 1N4007, on the cathode side.

--

JANA
_____


"ok" <binky@bonk.com> wrote in message
news:8jse615k36s922ou11vgb6aookrn30ghsj@4ax.com...
In the AC input to a child's RCA record player. (model 6-emp-2b,
couldn't find a schematic on line). It has 6, roughly 1/2" square
plates, mounted perpendicularly on a tube with a small amount of space
between each plate. It is painted a bright red- about an inch long.
Selenium Rectifier? It measures 2Mohm one direction and 1Mohm the
other. It has a screw which might be some type of adjustment or might
just be a fastener to keep the assembly together.
The unit motors and produces music at a whisper for 5 seconds and then
a real loud hum makes you turn it off.
Assuming the part is a rectifier can I replace it with a large diode?
5 amp? This thing has no transformer, one leg of the wall plug just
goes through the mystery part into a cap can and runs the motor and a
25L6 tube. Music must have been an electrifying part of many peoples
childhood in the two prong days. Thanks as always.

Archived from groups: rec.audio.tech (More info?)

JANA wrote:
> You will have to change both the rectifier, and the main filter
> capacitor(s). Take care that the polarization of these parts is
> important.
>
> You can use a silicon diode equivalent to 1N4007 (very common
> rectifier) to replace the selenium rectifier. Since the selenium
> rectifier normally goes opened, you can put the silicon diode right
> across it. This way the old diode becomes a terminal for the newer
> diode. The white band on the 1N4007 is the cathode side. The cathode
> side is the side that feeds to the + side of the filter caps. The
> white band would be where the + side is on the old diode.
>
> To reduce the in-rush effect of the startup, you can put a 5 Watt
> resistor of about 22 to 27 ohms in series with the 1N4007, on the
> cathode side.

This is all good advice, and in fact *should* be done if the unit is going
to actually be used regularly. The selenium rectifier 'will' fail sooner or
later, and emits some pretty toxic smoke when it does.

jak