Selenium rectifier testing ?

[N Cook]

In a valve Dansette Bermuda of early 60s
Been in a loft for years.
The mains wiring is perished and other wiring looks dodgy so testing some
things cold first.
Using 9V battery and 300 ohm dropper shows near enough 9V over the
rectifier, how high V do you have to go with a good one to check it ?
Are there safety grounds anyway for changing to a 1N4007 or so ?
Single element rectifier
Siemens lazy S logo
Made in Germany
2250c50
Kc 0.6e 11/16

 

[mike]

In a valve Dansette Bermuda of early 60s
Been in a loft for years.
The mains wiring is perished and other wiring looks dodgy so testing some
things cold first.
Using 9V battery and 300 ohm dropper shows near enough 9V over the
rectifier, how high V do you have to go with a good one to check it ?
Are there safety grounds anyway for changing to a 1N4007 or so ?
Single element rectifier
Siemens lazy S logo
Made in Germany
2250c50
Kc 0.6e 11/16

If you want to listen to the radio, there are lots better ways to do it.

OLD radios have emotional and monetary value just because they're old.
I never understood why people pay huge bux for something just because
it's old..."Hey, look at me, I just paid big bux for a radio that
sounds like crap!! But I got one of only 1000 in existence.
Ain't I cool?"...but I digress...

I suggest that both the emotional and monetary value of an old thing is
a strong function of it's "stockness". Stated another way, the
less stuff you change, the more value it has. Stated another way,
"If it ain't broke, don't fix it."

Put your effort into forming the caps before you plug it in.

 

[Jeff Liebermann]

In a valve Dansette Bermuda of early 60s
Been in a loft for years.
The mains wiring is perished and other wiring looks dodgy so testing some
things cold first.
Using 9V battery and 300 ohm dropper shows near enough 9V over the
rectifier, how high V do you have to go with a good one to check it ?
Dunno.

Are there safety grounds anyway for changing to a 1N4007 or so ?

Yes. The original selenium rectifier has a rather substantial forward
voltage drop. The design of the filters and the rest of the receiver
take this into consideration. When you replace it with a 1N4007, the
forward voltage drop will be MUCH less. Chances are good that you'll
apply too much voltage to the filter caps and receiver.

If you're going to simulate a selenium rectifier, you'll probably need
to add a series resistor to drop the voltage somewhat.

http://hhscott.com/cc/rectifiers.htm
http://wiki.answers.com/Q/Can_you_replace_a_selenium_rectifier_with_a_silicon_rectifier

Also, watch out for dead electrolytic filter capacitors. They will
need to be "reformed":

 

[[email protected]]

Yes. The original selenium rectifier has a rather substantial forward
voltage drop. The design of the filters and the rest of the receiver
take this into consideration. When you replace it with a 1N4007, the
forward voltage drop will be MUCH less. Chances are good that you'll
apply too much voltage to the filter caps and receiver.

If you're going to simulate a selenium rectifier, you'll probably need
to add a series resistor to drop the voltage somewhat.

http://hhscott.com/cc/rectifiers.ht...Q/Can_you_replace_a_selenium_rectifier_with_a...

Also, watch out for dead electrolytic filter capacitors. They will
need to be "reformed":


--
Jeff Liebermann [email protected]
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

I would look at the working voltage rating of the original
electrolytics and make sure that the voltage which you apply with the
new silicon diode does not exceed 85 percent of it. Use a variac to do
this. It will also reform the electrolytics at the same time. But a a
previous posted said if the selenium unit is ok then I wouldn't bother
to replace it. Lenny Stein Barlen Electronics.

 

[James Sweet]

If you want to listen to the radio, there are lots better ways to do it.

OLD radios have emotional and monetary value just because they're old.
I never understood why people pay huge bux for something just because it's
old..."Hey, look at me, I just paid big bux for a radio that
sounds like crap!! But I got one of only 1000 in existence.
Ain't I cool?"...but I digress...

Well you may not agree with it, but it's certainly a common human thing to
do. People pay big bucks for things a lot less useful than an old radio, one
needs only to walk past a jewelry store to observe this. Diamonds are good
for cutting things, that's my view, but obviously a whole lot of people
disagree with me.

That said, there's just nothing quite like listening to an old radio,
definitely an emotional component to it, my '37 Zenith console is the only
radio I ever listen to.

 

[jakdedert]

In a valve Dansette Bermuda of early 60s
Been in a loft for years.
The mains wiring is perished and other wiring looks dodgy so testing some
things cold first.
Using 9V battery and 300 ohm dropper shows near enough 9V over the
rectifier, how high V do you have to go with a good one to check it ?
Are there safety grounds anyway for changing to a 1N4007 or so ?
Single element rectifier
Siemens lazy S logo
Made in Germany
2250c50
Kc 0.6e 11/16

Ask in rec.antiques.radio+phono...or just google the subject in that
forum. It's been discussed at length. The general outcome is that yes,
you should replace the selenium with silicon. It's prone to self
destruct, and if it does, it emits nasty--some say toxic--fumes. (IOW
the magic smoke contained therein can harm you.)

There is a greater voltage drop across selenium. A series resister
should be added to compensate, calculated according to average B+
voltage/current.

jak

 

[mike]

Well you may not agree with it, but it's certainly a common human thing to
do. People pay big bucks for things a lot less useful than an old radio, one
needs only to walk past a jewelry store to observe this. Diamonds are good
for cutting things, that's my view, but obviously a whole lot of people
disagree with me.

That said, there's just nothing quite like listening to an old radio,
definitely an emotional component to it, my '37 Zenith console is the only
radio I ever listen to.

Post a picture of the rig you use to take that zenith jogging.

I agree, I just don't practice.

I can think of only one old thing that I wish I still had...nope,
I really don't want her back either... ;-)

Out with the old, in with the fully depreciated...

 

[N Cook]

Ask in rec.antiques.radio+phono...or just google the subject in that
forum. It's been discussed at length. The general outcome is that yes,
you should replace the selenium with silicon. It's prone to self
destruct, and if it does, it emits nasty--some say toxic--fumes. (IOW
the magic smoke contained therein can harm you.)

There is a greater voltage drop across selenium. A series resister
should be added to compensate, calculated according to average B+
voltage/current.

jak

The owner likes the smell contained within, on lifting the lid.
Taking it apart it is even stronger old radio smell.
Does the selenium rectifier add to the smell in any way ? so replacing it
would "lessen the experience" ?

 

[Ron(UK)]

Does the selenium rectifier add to the smell in any way ?

They certainly do when they fail!

Ron(UK)

 

[James Sweet]

Post a picture of the rig you use to take that zenith jogging.

I agree, I just don't practice.

I can think of only one old thing that I wish I still had...nope,
I really don't want her back either... ;-)

Out with the old, in with the fully depreciated...

I take my iPod jogging, I listen to CDs in the car, the content on either is
far superior, but it's not the same experience as sitting by the fire near
the warm glow of a classic radio. It's not about the content or the sound
quality.

 

[[email protected]]

In a valve Dansette Bermuda of early 60s
Been in a loft for years.
The mains wiring is perished and other wiring looks dodgy so testing some
things cold first.
Using 9V battery and 300 ohm dropper shows near enough 9V over the
rectifier, how high V do you have to go with a good one to check it ?
Are there safety grounds anyway for changing to a 1N4007 or so ?
Single element rectifier
Siemens lazy S logo
Made in Germany
2250c50
Kc 0.6e 11/16

Mpffff... let's try to answer the question, at least a little bit.

a) The OEM selenium diode is prone to failure. When it fails it does
so in a spectacular manner such that you will offend any and all
parties within smell-range and at the same time release fumes that are
toxic (but by no means as toxic as they smell). So: Get rid of it.
Better yet, leave it in place for appearance but hide the new silicon
diode behind it.

b) There is a significant voltage-drop across the diode. In battery
sets (typically with 1.4V tubes, not accounting for this drop can
either greatly shorten tube life *or* blow filaments altogether.

c) As selenium diodes age, they increase in resistance. Many battery
sets (with specific reference to the post-war, miniature-tube Zenith
TransOceanic series) will fail due to too-low filament voltage from
this cause. On the other hand, with some of their mains-only radios,
with specific reference to the post-war AM/FM units, this is not a
major issue.

So: Yes, replace the diode. Add a resistor in series to get the proper
filament voltage if this is a concern. For the T/O series, that can
work out somewhere between 30 and 80 ohms @ 2 watts (use 5 if you can)
or better. Such a resistor is harder to conceal than the diode, but it
does make the radio functional with reasonable safety. But if the down-
line components from the rectifier are not voltage-sensitive, you may
not have to add the dropping resistor.

Now, keep in mind that if you are replacing a single selenium diode
(i.e.: NOT a stack), the forward voltage drop is insignificant such
that no additional resistor is required. Or, you can put a zener diode
across the filament string (if so equipped), to protect the tubes.

Peter Wieck
Wyncote, PA

 

[mike]

I take my iPod jogging, I listen to CDs in the car, the content on either is
far superior, but it's not the same experience as sitting by the fire near
the warm glow of a classic radio. It's not about the content or the sound
quality.

I picked up a pair of Dynaco Monoblock amplifiers at a garage sale.
Hooked 'em up and couldn't tell that they sounded any different.
Definitely winter weather amplifiers. Coulda roasted wieners on 'em.
Luckily, I found someone who thought they did sound better and offered
me 10x what I paid for them. Out they went. I live in a no-nostalgia
zone. ;-)

 

[Tim Schwartz]

In a valve Dansette Bermuda of early 60s
Been in a loft for years.
The mains wiring is perished and other wiring looks dodgy so testing some
things cold first.
Using 9V battery and 300 ohm dropper shows near enough 9V over the
rectifier, how high V do you have to go with a good one to check it ?
Are there safety grounds anyway for changing to a 1N4007 or so ?
Single element rectifier
Siemens lazy S logo
Made in Germany
2250c50
Kc 0.6e 11/16

Nigel,

Take another look at the number. Might it be "B250C50"? Many European
rectifiers used to give you the voltage (B, in this case 250 volts) and
current rating (C, in this case 50mA) of the device.

I agree with the other posters that you can replace the selenium with a
silicon diode, but may need to ad a dropping resistor as the B+ may be
higher because of less loss in the rectifier. I usually bring the item
up slowly on a variac and make sure that I don't exceed the voltage
of the filter caps. Better still if you have a factory diagram telling
you what the B+ is supposed to be. Then you can choose an appropriate
resistor, and you might need quite a few watts worth too.

Unfortunately, I can't suggest how you might test the selenium.

Regards,
Tim Schwartz
Bristol Electronics

 

[N Cook]

Nigel,

Take another look at the number. Might it be "B250C50"? Many European
rectifiers used to give you the voltage (B, in this case 250 volts) and
current rating (C, in this case 50mA) of the device.

I agree with the other posters that you can replace the selenium with a
silicon diode, but may need to ad a dropping resistor as the B+ may be
higher because of less loss in the rectifier. I usually bring the item
up slowly on a variac and make sure that I don't exceed the voltage
of the filter caps. Better still if you have a factory diagram telling
you what the B+ is supposed to be. Then you can choose an appropriate
resistor, and you might need quite a few watts worth too.

Unfortunately, I can't suggest how you might test the selenium.

Regards,
Tim Schwartz
Bristol Electronics

I have a1979 Siemens databook and E250C50 were still listed,
rating only 200V, 20mA

I removed and tried on a bench supply thru 330 ohms.
Took to 25V and read over the rectifier 25V, powered either way

So will replace with silicon

 

[James Sweet]

Nigel,

Take another look at the number. Might it be "B250C50"? Many European
rectifiers used to give you the voltage (B, in this case 250 volts) and
current rating (C, in this case 50mA) of the device.

I agree with the other posters that you can replace the selenium with a
silicon diode, but may need to ad a dropping resistor as the B+ may be
higher because of less loss in the rectifier. I usually bring the item up
slowly on a variac and make sure that I don't exceed the voltage
of the filter caps. Better still if you have a factory diagram telling you
what the B+ is supposed to be. Then you can choose an appropriate
resistor, and you might need quite a few watts worth too.

Unfortunately, I can't suggest how you might test the selenium.

There isn't realy any reason to test them. Given how nasty it is when they
fail, and how likely that is to occur, I replace them any time I encounter
them.

 

[Reinhard Zwirner]

....

Nigel,

Take another look at the number. Might it be "B250C50"?

"B" stands for _B_rücken-Gleichrichter (bridge rectifier), whereas
"E" stands for _E_inweg-Gleichrichter (half-wave rectifier).

250: rated voltage = 250 V
"C" stands for _c_apacitive load.
50: rated current with capative load = 50 mA

HTH

Reinhard