I just finished re-capping and replacing out of tolerance resisters on a model B 600 Zenith T/O. It works great but want to go ahead and replace the selenium rectifier before it goes bad. I have been searching the internet on this but am getting conflicting information. Can anyone supply the proper components and values along with a diagram?
Many thanks,
Jon.

Hi Jon

Selenium rectifiers can be replaced with 1N4004 - 1N4007 silicon diodes. The band end is same as + on a selenium rectifier. Remove one wire from the selemium rectifier to isolate from the circuit.

A small value resistor should be added in series with a silicon diode. A silicon diode drops .7 volts while selenium rectifier around 7 volts. The exact value is determined by current being drawn. I would use a 47 ohm 1 or 2 watt resistor and measure voltages.

Norm

: I just finished re-capping and replacing out of tolerance resisters on a model B 600 Zenith T/O. It works great but want to go ahead and replace the selenium rectifier before it goes bad. I have been searching the internet on this but am getting conflicting information. Can anyone supply the proper components and values along with a diagram?
:Many thanks,
:Jon.

Jon

If the radio is working and the voltages are correct I would leave the selenium alone, it is a much better rectifier than a silicon diode.

Dave

Dave:.... Really? Is Selinium better than silicon? ... news to me!
I thought selinium was a relatively poor rectifier. I thought it had a much lower font to back ratio and a higher voltage drop.
This is not really based on any great "reasearch" just experience and the fact that they went the way of the buggy whip as soon as silicon came along... so what's the scoop poop? What's data backing yer claim there cowboy?

If the selenium rectifier has no reverse leakage (check with your multi-meter with the X10,000 ohm scale), leave it alone. It'll perform well for years if you don't expose it to moisture or have old electrolytics in place. If you replace the electrolytics and other condensers, there's little chance for a short, and so it'll be fine. If you ever accidently overload it, it should be checked again. I have several pieces of equipment that use selenium rectifiers, that I use every day, sometimes for hours. The rectifiers don't usually fail. If you want to be on the safe side, replace it or fuse it. I think that they're pretty trustworthy, though.

Thomas

Hi Jon

As others have said if your radio is working well you don't have to change the selenium rectifier. Measure voltage to be sure it's high enough.

There are a couple concerns with selenium rectifiers. Voltage drop can go up over time even without use. A selenium rectifier should have 7 volts drop. I've seen new ones several times this.

The biggest concern is smell. If something happens and a selenium rectifier shorts it will burn and smell. Nothing is worse than the smell of a smoking selenium rectifier.

Norm

:If the selenium rectifier has no reverse leakage (check with your multi-meter with the X10,000 ohm scale), leave it alone. It'll perform well for years if you don't expose it to moisture or have old electrolytics in place. If you replace the electrolytics and other condensers, there's little chance for a short, and so it'll be fine. If you ever accidently overload it, it should be checked again. I have several pieces of equipment that use selenium rectifiers, that I use every day, sometimes for hours. The rectifiers don't usually fail. If you want to be on the safe side, replace it or fuse it. I think that they're pretty trustworthy, though.
:
:Thomas

:If the selenium rectifier has no reverse leakage (check with your multi-meter with the X10,000 ohm scale), leave it alone. It'll perform well for years if you don't expose it to moisture or have old electrolytics in place. If you replace the electrolytics and other condensers, there's little chance for a short, and so it'll be fine. If you ever accidently overload it, it should be checked again. I have several pieces of equipment that use selenium rectifiers, that I use every day, sometimes for hours. The rectifiers don't usually fail. If you want to be on the safe side, replace it or fuse it. I think that they're pretty trustworthy, though.
:
:Thomas

From US Mil Standard Handbook 1004/10
Section 6.5.3.8

"Ordinary selenium stacks deteriorate with time. This "aging" can
be reduced by variations in plate composition and "non-aging" stacks are
available. Aging rates are determined by operating temperatures that are a
function of current flow. The selection of a unit using selenium rectifying
elements which has a somewhat greater capacity than required will increase
stack life. The efficiency of selenium rectifying elements is a function of
operating voltage versus rated voltage as shown in Figure 41.
Silicon diodes are mounted in metal cases which are mounted on
either aluminum or copper plates to dissipate the heat generated during
operation. Silicon diodes do not age as do selenium stacks and, as shown in
Figure 42, are more efficient than selenium elements, particularly at higher
voltage ratings."

Replace them now / replace them later. You will eventually replace selenium units.

Rich

True, true. They do fail eventually, and are not as stable as silicon rectifiers. If you really feel that you must replace your selenium rectifier, go for it. I just want to stress the point that after 50 or 60 years, many still work fine, and reliably. I should say that chances are that a 50 year old one is more likely to work than a 60 year old one, though. I think that manufacturing techniques improved by the 1950s. I've had several from the 1940s that were crap. I have had my share of portable phonographs, though, that work fine and continue to work. Most of them I have given away, but I still have one with a selenium element that works fine. I had one RCA Victor Orthophonic High Fidelity table model that did have a leaky rectifier. The hum wouldn't go away even after electrolytic replacement, and so I tested the rectifier to find that it leaked in both directions. Leaky rectifiers can also damage electrolytics.

I also have my Semco Page Boy Baby Sitter Transmitter, which I've used for hours with no problems. Interestingly enough the rectifier in this unit is not sealed with paint.

I have a small Zenith portable that has a selenium rectifier. The radio works very well. I don't use it often, but it always powers up well. It even has its original electrolytics. I have found that a lot of old Zenith portables still have good electrolytics. Zenith seems to have used a very high quality electrolytic during this time period (1940s on). Maybe that's just my experience. I think that it's more of a 50/50 chance that you're going to get a Zenith with good electrolytics because I've heard plenty of stories leaning in both directions.

The seleniums do go bad, but they can be quite reliable, too. Sorry for the oxymoron there. Fusing is always a plus. The fuse will protect the radio. I don't want to give people false security, but in the case of seleniums I feel that it is better to test them first instead of simply replacing them (though replacement is simple and inexpensive). I feel that they are a bit more reliable than paper condensers.

Thomas

:
:From US Mil Standard Handbook 1004/10
:Section 6.5.3.8
:
:"Ordinary selenium stacks deteriorate with time. This "aging" can
:be reduced by variations in plate composition and "non-aging" stacks are
:available. Aging rates are determined by operating temperatures that are a
:function of current flow. The selection of a unit using selenium rectifying
:elements which has a somewhat greater capacity than required will increase
:stack life. The efficiency of selenium rectifying elements is a function of
:operating voltage versus rated voltage as shown in Figure 41.
:Silicon diodes are mounted in metal cases which are mounted on
:either aluminum or copper plates to dissipate the heat generated during
:operation. Silicon diodes do not age as do selenium stacks and, as shown in
:Figure 42, are more efficient than selenium elements, particularly at higher
:voltage ratings."
:
:Replace them now / replace them later. You will eventually replace selenium units.
:
:Rich
:

:True, true. They do fail eventually, and are not as stable as silicon rectifiers. If you really feel that you must replace your selenium rectifier, go for it. I just want to stress the point that after 50 or 60 years, many still work fine, and reliably. I should say that chances are that a 50 year old one is more likely to work than a 60 year old one, though. I think that manufacturing techniques improved by the 1950s. I've had several from the 1940s that were crap. I have had my share of portable phonographs, though, that work fine and continue to work. Most of them I have given away, but I still have one with a selenium element that works fine. I had one RCA Victor Orthophonic High Fidelity table model that did have a leaky rectifier. The hum wouldn't go away even after electrolytic replacement, and so I tested the rectifier to find that it leaked in both directions. Leaky rectifiers can also damage electrolytics.
:
:I also have my Semco Page Boy Baby Sitter Transmitter, which I've used for hours with no problems. Interestingly enough the rectifier in this unit is not sealed with paint.
:
:I have a small Zenith portable that has a selenium rectifier. The radio works very well. I don't use it often, but it always powers up well. It even has its original electrolytics. I have found that a lot of old Zenith portables still have good electrolytics. Zenith seems to have used a very high quality electrolytic during this time period (1940s on). Maybe that's just my experience. I think that it's more of a 50/50 chance that you're going to get a Zenith with good electrolytics because I've heard plenty of stories leaning in both directions.
:
:The seleniums do go bad, but they can be quite reliable, too. Sorry for the oxymoron there. Fusing is always a plus. The fuse will protect the radio. I don't want to give people false security, but in the case of seleniums I feel that it is better to test them first instead of simply replacing them (though replacement is simple and inexpensive). I feel that they are a bit more reliable than paper condensers.
:
:Thomas
:
: :
::From US Mil Standard Handbook 1004/10
::Section 6.5.3.8
::
::"Ordinary selenium stacks deteriorate with time. This "aging" can
::be reduced by variations in plate composition and "non-aging" stacks are
::available. Aging rates are determined by operating temperatures that are a
::function of current flow. The selection of a unit using selenium rectifying
::elements which has a somewhat greater capacity than required will increase
::stack life. The efficiency of selenium rectifying elements is a function of
::operating voltage versus rated voltage as shown in Figure 41.
::Silicon diodes are mounted in metal cases which are mounted on
::either aluminum or copper plates to dissipate the heat generated during
::operation. Silicon diodes do not age as do selenium stacks and, as shown in
::Figure 42, are more efficient than selenium elements, particularly at higher
::voltage ratings."
::
::Replace them now / replace them later. You will eventually replace selenium units.
::
::Rich

Wow-thanks to all that responded to my query. I tested the rectifier and it showed no problem. As this is going to be a gift to a relative, I went ahead and replaced with silicon diode and resister as stated. I just did not want to risk it. Voltages were fine. If I was going to keep it I would have left it alone.
Again many thanks to the always good and entertaining advice.
Jon.
::

::True, true. They do fail eventually, and are not as stable as silicon rectifiers. If you really feel that you must replace your selenium rectifier, go for it. I just want to stress the point that after 50 or 60 years, many still work fine, and reliably. I should say that chances are that a 50 year old one is more likely to work than a 60 year old one, though. I think that manufacturing techniques improved by the 1950s. I've had several from the 1940s that were crap. I have had my share of portable phonographs, though, that work fine and continue to work. Most of them I have given away, but I still have one with a selenium element that works fine. I had one RCA Victor Orthophonic High Fidelity table model that did have a leaky rectifier. The hum wouldn't go away even after electrolytic replacement, and so I tested the rectifier to find that it leaked in both directions. Leaky rectifiers can also damage electrolytics.
::
::I also have my Semco Page Boy Baby Sitter Transmitter, which I've used for hours with no problems. Interestingly enough the rectifier in this unit is not sealed with paint.
::
::I have a small Zenith portable that has a selenium rectifier. The radio works very well. I don't use it often, but it always powers up well. It even has its original electrolytics. I have found that a lot of old Zenith portables still have good electrolytics. Zenith seems to have used a very high quality electrolytic during this time period (1940s on). Maybe that's just my experience. I think that it's more of a 50/50 chance that you're going to get a Zenith with good electrolytics because I've heard plenty of stories leaning in both directions.
::
::The seleniums do go bad, but they can be quite reliable, too. Sorry for the oxymoron there. Fusing is always a plus. The fuse will protect the radio. I don't want to give people false security, but in the case of seleniums I feel that it is better to test them first instead of simply replacing them (though replacement is simple and inexpensive). I feel that they are a bit more reliable than paper condensers.
::
::Thomas
::
:: :
:::From US Mil Standard Handbook 1004/10
:::Section 6.5.3.8
:::
:::"Ordinary selenium stacks deteriorate with time. This "aging" can
:::be reduced by variations in plate composition and "non-aging" stacks are
:::available. Aging rates are determined by operating temperatures that are a
:::function of current flow. The selection of a unit using selenium rectifying
:::elements which has a somewhat greater capacity than required will increase
:::stack life. The efficiency of selenium rectifying elements is a function of
:::operating voltage versus rated voltage as shown in Figure 41.
:::Silicon diodes are mounted in metal cases which are mounted on
:::either aluminum or copper plates to dissipate the heat generated during
:::operation. Silicon diodes do not age as do selenium stacks and, as shown in
:::Figure 42, are more efficient than selenium elements, particularly at higher
:::voltage ratings."
:::
:::Replace them now / replace them later. You will eventually replace selenium units.
:::
:::Rich
:
:Wow-thanks to all that responded to my query. I tested the rectifier and it showed no problem. As this is going to be a gift to a relative, I went ahead and replaced with silicon diode and resister as stated. I just did not want to risk it. Voltages were fine. If I was going to keep it I would have left it alone.
:Again many thanks to the always good and entertaining advice.
:Jon.
:::

Good decision!

I just found this on the Internet from the Corps of Engineers:

SAFETRAN Systems Customer Service
Bulletin, No. CSB1-99, dated January 25,
1999. The
selenium material
used on the
Power Off Shelf
Relay Rectifer
(040387-AYX)
has a natural
leakage or aging
process that will
weaken the rectifier over time. Normal
life expectancy of these selenium
rectifiers is 9 to 15 years. However, the
aging process can be accelerated by
environmental conditions.

Rich
*************************

On another forum I have been asking for a bad selenium from a radio, I have been waiting for three years now and nobody has been able to produce one.

A selenium can be short circuited without damage, this will destroy a silicon diode. A selenium can take excessive voltage spikes without damage, a silicon diode will be destroyed. A selenium has a slow start, a silicon diode does not. A selenium does not produce RFI, a silicon does. If a selenium fails it will fail open, when a silicon fails it will fail shorted (there go your expensive tubes) There is no proof that anybody has been harmed by the odor of a failed selenium.

Most any high current, heavy-duty power supplys will have selenium, ie: welders, battery chargers, electro-plating, etc. Selenium devices are still being produced today. MOV's are a good example. The only time I have seen a selenium fail in a radio is if the filter caps or some other component has shorted.

I would suggest if you are going to use a silicon, put two of them in series because one of them will short, also fuse your radio, this may save your tubes but I wouldn't guarantee it. You will also have to adjust your surge resistor to obtain the proper filament voltage, this is very critical especially in battery radios. The cost of seleniums is the reason they are no longer used in radios (some european radios still use them) All of my radios and equipment still have their seleniums, and operate just fine. I have been doing this for fifty years now and will stick with seleniums. You can make up your own mind.

Dave

:On another forum I have been asking for a bad selenium from a radio, I have been waiting for three years now and nobody has been able to produce one.
:
:A selenium can be short circuited without damage, this will destroy a silicon diode. A selenium can take excessive voltage spikes without damage, a silicon diode will be destroyed. A selenium has a slow start, a silicon diode does not. A selenium does not produce RFI, a silicon does. If a selenium fails it will fail open, when a silicon fails it will fail shorted (there go your expensive tubes) There is no proof that anybody has been harmed by the odor of a failed selenium.
:
:Most any high current, heavy-duty power supplys will have selenium, ie: welders, battery chargers, electro-plating, etc. Selenium devices are still being produced today. MOV's are a good example. The only time I have seen a selenium fail in a radio is if the filter caps or some other component has shorted.
:
:I would suggest if you are going to use a silicon, put two of them in series because one of them will short, also fuse your radio, this may save your tubes but I wouldn't guarantee it. You will also have to adjust your surge resistor to obtain the proper filament voltage, this is very critical especially in battery radios. The cost of seleniums is the reason they are no longer used in radios (some european radios still use them) All of my radios and equipment still have their seleniums, and operate just fine. I have been doing this for fifty years now and will stick with seleniums. You can make up your own mind.
:
:Dave
:
Dave,

I like vacuum tubes. I've used them for 50 yrs. But no one designs with vacuum tubes any more. No one in this country has designed selenium into a welder for over 30 yrs. Maybe the Chinese still use it in battery chargers? You sell selenium, so you like it. There is a reason why no major manufacturers make selenium today. It's obsolete! How much does a 1 amp / 400 volt selenium stack cost? A 1N4004 costs about a dime.
Rich

:On another forum I have been asking for a bad selenium from a radio, I have been waiting for three years now and nobody has been able to produce one.
:
:A selenium can be short circuited without damage, this will destroy a silicon diode. A selenium can take excessive voltage spikes without damage, a silicon diode will be destroyed. A selenium has a slow start, a silicon diode does not. A selenium does not produce RFI, a silicon does. If a selenium fails it will fail open, when a silicon fails it will fail shorted (there go your expensive tubes) There is no proof that anybody has been harmed by the odor of a failed selenium.
:
:Most any high current, heavy-duty power supplys will have selenium, ie: welders, battery chargers, electro-plating, etc. Selenium devices are still being produced today. MOV's are a good example. The only time I have seen a selenium fail in a radio is if the filter caps or some other component has shorted.
:
:I would suggest if you are going to use a silicon, put two of them in series because one of them will short, also fuse your radio, this may save your tubes but I wouldn't guarantee it. You will also have to adjust your surge resistor to obtain the proper filament voltage, this is very critical especially in battery radios. The cost of seleniums is the reason they are no longer used in radios (some european radios still use them) All of my radios and equipment still have their seleniums, and operate just fine. I have been doing this for fifty years now and will stick with seleniums. You can make up your own mind.
:
:Dave
:

PS: MOVs are not selenium devices. Metal Oxide Varistors are made with magnesium or zinc oxide. Back in the old days we used to make selenium VoltTraps and Thyrectors. MOVs wiped out that business 25 yrs. ago.

Rich

Hi Dave

I was going to comment on the other forum but might as well do it here.

Can't agree with everything. Short a selenium rectifier and it will burn. There will be bubbles on the plates and the worst smell you have ever noticed. Once you smell a selenium rectifier burning you will never forget it..

Two silicon diodes in series doesn't help unless voltage rating isn't high enough. Short an electrolytic and they both burn up.

You can get silicon diodes 100 amps and more. Some rectifiers with plates, that look like selenium, have silicon diodes mounted on them.

Norm

:On another forum I have been asking for a bad selenium from a radio, I have been waiting for three years now and nobody has been able to produce one.
:
:A selenium can be short circuited without damage, this will destroy a silicon diode. A selenium can take excessive voltage spikes without damage, a silicon diode will be destroyed. A selenium has a slow start, a silicon diode does not. A selenium does not produce RFI, a silicon does. If a selenium fails it will fail open, when a silicon fails it will fail shorted (there go your expensive tubes) There is no proof that anybody has been harmed by the odor of a failed selenium.
:
:Most any high current, heavy-duty power supplys will have selenium, ie: welders, battery chargers, electro-plating, etc. Selenium devices are still being produced today. MOV's are a good example. The only time I have seen a selenium fail in a radio is if the filter caps or some other component has shorted.
:
:I would suggest if you are going to use a silicon, put two of them in series because one of them will short, also fuse your radio, this may save your tubes but I wouldn't guarantee it. You will also have to adjust your surge resistor to obtain the proper filament voltage, this is very critical especially in battery radios. The cost of seleniums is the reason they are no longer used in radios (some european radios still use them) All of my radios and equipment still have their seleniums, and operate just fine. I have been doing this for fifty years now and will stick with seleniums. You can make up your own mind.
:
:Dave
:

:Hi Dave
:
: I was going to comment on the other forum but might as well do it here.
:
: Can't agree with everything. Short a selenium rectifier and it will burn. There will be bubbles on the plates and the worst smell you have ever noticed. Once you smell a selenium rectifier burning you will never forget it..
:
: Two silicon diodes in series doesn't help unless voltage rating isn't high enough. Short an electrolytic and they both burn up.
:
: You can get silicon diodes 100 amps and more. Some rectifiers with plates, that look like selenium, have silicon diodes mounted on them.
:
:Norm
:
Norm, I should have explained a bit better, it takes milli seconds for a silicon to fry when short circuited whereas the selenium takes seconds. I know what they smell like, I fried my share of them in the old days, it was amazing the abuse they would take.

The idea of putting the diodes in series was not to raise the voltage rating but to help protect against powerline spikes, hopefully only one would short.

I have some 300 amp silicon here in the shop, they were used in a xenon lamp power supply.

Dave

You just can't convince some people. People hear a rumor and they just keep spreading it like crazy. You're totally right about the seleniums. If they only lasted 15 years, then why are there so many 50 and 60 year old radios still working with them (including this guy's Transoceanic)? Also, as I've said before, I have a couple of very recently made battery chargers made here in the U.S. that have seleniums in them. My friend's body shop has some 10 year old welders with selenium stacks in them. They're totally reliable and fine. People panic, though. That's why you see so many over-safety minded people freaking out about polarized line cords on AC-DC radios, etc. I'd say that these people obsess on meaningless things. Just use the selenium rectifier and tell people not to touch the chassis of an AC-DC radio. Simple as that. You can't convince some people, though, and you never will. You've got people all over the place who say that Japanese cars are crap. As much as I'd love it if U.S. cars were great, they aren't. If U.S. car manufacturers could produce wonderful cars, I'd stand behind them all the way. They say they advance, and they don't really. I don't know why people are so blind, but Japanese cars last forever without any maintainence, and they don't burn oil all over the place like every Ford and Chrysler. Still, you'll always have people who say that they're junk. You'll always have people who say that selenium rectifiers are junk, too, not necessarily with any hard facts to back them up.

I'm sure that this subject will come up again and again, though. I'm really getting sick of it. I'm sure that if you short out a selenium, it'll stink, but they otherwise just don't fail. They're great. Just don't overload them or soak them in water.

Thomas

One more note on seleniums. A friend of mine owns a business, Select Sound Service, that happens to have the world's largest antique microphone museum. His freight elevator originally used a motor-generator in order to create the direct current needed by the elevator motor. The unit dates to about 1900. In the 1950s a very large selenium rectifier set-up was installed, and is still used to this day every day. The unit is only turned off at the end of the day. Otherwise it is on all day long so that the elevator may be used at any time. The motor-generator is still wired up and may be used in the event that the rectifier fails (the motor still works, too....it is huge and awesome!), but the rectifier has never failed.

Thomas

I would agree if the devices are working, why replace them? Selenium has it place, the same with silicon, and if the design is done right, both will last a long time (this includes designing in protection for either devices to handle voltage spikes or short circuits (i.e., use of fuses).

David S.

:One more note on seleniums. A friend of mine owns a business, Select Sound Service, that happens to have the world's largest antique microphone museum. His freight elevator originally used a motor-generator in order to create the direct current needed by the elevator motor. The unit dates to about 1900. In the 1950s a very large selenium rectifier set-up was installed, and is still used to this day every day. The unit is only turned off at the end of the day. Otherwise it is on all day long so that the elevator may be used at any time. The motor-generator is still wired up and may be used in the event that the rectifier fails (the motor still works, too....it is huge and awesome!), but the rectifier has never failed.
:
:Thomas