Ok so i have some sets that i use pretty frequently, and i am afraid of the dreaded rectifier failure i have heard so much about, but i am somewhat lacking in cash to send these radios across the world to get fixd, so i was wondering if someone could help me out or walk me through the process.... the models are as follows: 1) zenith k731 2) zenith hifi h840 3) a zenith chassis from the 40s, not sure of model number, and a small plastic am/fm zenith set. these are my babys any help would be so appreciated, i know basic soldering but am pretty new to all of this, i just know i love these radios =) thanks so much and best regards

:Ok so i have some sets that i use pretty frequently, and i am afraid of the dreaded rectifier failure i have heard so much about, but i am somewhat lacking in cash to send these radios across the world to get fixd, so i was wondering if someone could help me out or walk me through the process.... the models are as follows: 1) zenith k731 2) zenith hifi h840 3) a zenith chassis from the 40s, not sure of model number, and a small plastic am/fm zenith set. these are my babys any help would be so appreciated, i know basic soldering but am pretty new to all of this, i just know i love these radios =) thanks so much and best regards
:
Hi Bjorn:

Yes a selenium diode can smell pretty bad when and if it fails. However if the radios you are using have had good or new quality filter caps put in the power supply already then there is less of a chance for the selenium rectifier to fail.

It is also true that selenium rectifiers are not as "bullet proof" or as efficient as the newer type superior silicon rectifiers.

So if you wish to replace the selenium rectifier in any particular radio "just to be on the safe side" you can easily do it.

The suggested replacement recifier of choice quite often is the 1n4007 diode. It is very cheap ( only a few cents) and has a high inversre voltage rating of 1000v.

When replacing a selenium with a silicon diode the area of primary concern is that the selenium has a measurable voltage drop across it and the silicon diode has almost none.

So the DC voltage in your power supply as measured right after the selenium rectifier would be lower than that when a silicon is used.

So typically when a silicon diode replaces a selenium most folks add a 300 ohm 2 watt resistor or such in series to keep the same voltage level as before.

:Ok so i have some sets that i use pretty frequently, and i am afraid of the dreaded rectifier failure i have heard so much about, but i am somewhat lacking in cash to send these radios across the world to get fixd, so i was wondering if someone could help me out or walk me through the process.... the models are as follows: 1) zenith k731 2) zenith hifi h840 3) a zenith chassis from the 40s, not sure of model number, and a small plastic am/fm zenith set. these are my babys any help would be so appreciated, i know basic soldering but am pretty new to all of this, i just know i love these radios =) thanks so much and best regards
:
Hi Bjorn,
I have to admit that I differ from Peter on this. I recommend that you do not replace the diodes.
I have restored several of the Zenith H724 type radios and know where you can go wrong. Replacement of the diode is simple and the one Peter mentioned would work well.
However, the resistor replacement can be problematic, as the size to use is not obvious. A 300 ohm value will not work for all radios.
The H724's have a 22 ohm 2 watt resistor. It needs to change to a 60 ohm 3 watt resistor. This was found through trial and error after checking the plate voltages of the tubes.
If the resistor you use is too small, or you leave the one already in there the filter capacitors are eventually destroyed. If the resistor is too high, performance will suffer.
Zenith used high quality capacitors in these radios during this period. Almost all Zeniths from this period I restore have their original filters. I keep them because they test as new.

My recommendaiton is that you not replace the selenium rectifiers, just enjoy them.

Best Regards,

Bill Grimm

::Ok so i have some sets that i use pretty frequently, and i am afraid of the dreaded rectifier failure i have heard so much about, but i am somewhat lacking in cash to send these radios across the world to get fixd, so i was wondering if someone could help me out or walk me through the process.... the models are as follows: 1) zenith k731 2) zenith hifi h840 3) a zenith chassis from the 40s, not sure of model number, and a small plastic am/fm zenith set. these are my babys any help would be so appreciated, i know basic soldering but am pretty new to all of this, i just know i love these radios =) thanks so much and best regards
::
:Hi Bjorn,
: I have to admit that I differ from Peter on this. I recommend that you do not replace the diodes.
: I have restored several of the Zenith H724 type radios and know where you can go wrong. Replacement of the diode is simple and the one Peter mentioned would work well.
: However, the resistor replacement can be problematic, as the size to use is not obvious. A 300 ohm value will not work for all radios.
: The H724's have a 22 ohm 2 watt resistor. It needs to change to a 60 ohm 3 watt resistor. This was found through trial and error after checking the plate voltages of the tubes.
: If the resistor you use is too small, or you leave the one already in there the filter capacitors are eventually destroyed. If the resistor is too high, performance will suffer.
: Zenith used high quality capacitors in these radios during this period. Almost all Zeniths from this period I restore have their original filters. I keep them because they test as new.
:
: My recommendaiton is that you not replace the selenium rectifiers, just enjoy them.
:
:Best Regards,
:
:Bill Grimm
:
Lewis

x

:Ok so i have some sets that i use pretty frequently, and i am afraid of the dreaded rectifier failure i have heard so much about, but i am somewhat lacking in cash to send these radios across the world to get fixd, so i was wondering if someone could help me out or walk me through the process.... the models are as follows: 1) zenith k731 2) zenith hifi h840 3) a zenith chassis from the 40s, not sure of model number, and a small plastic am/fm zenith set. these are my babys any help would be so appreciated, i know basic soldering but am pretty new to all of this, i just know i love these radios =) thanks so much and best regards
:
Bjorn...

there are lots of pros and cons about changing selenium.

It relatively easy to do.

http://www.w3hwj.com/index_files/RBSelenium2.pdf

I hope this helps.

Rich

::Ok so i have some sets that i use pretty frequently, and i am afraid of the dreaded rectifier failure i have heard so much about, but i am somewhat lacking in cash to send these radios across the world to get fixd, so i was wondering if someone could help me out or walk me through the process.... the models are as follows: 1) zenith k731 2) zenith hifi h840 3) a zenith chassis from the 40s, not sure of model number, and a small plastic am/fm zenith set. these are my babys any help would be so appreciated, i know basic soldering but am pretty new to all of this, i just know i love these radios =) thanks so much and best regards
::
:
:
:Bjorn...
:
:there are lots of pros and cons about changing selenium.
:
:It relatively easy to do.
:
:http://www.w3hwj.com/index_files/RBSelenium2.pdf
:
:I hope this helps.
:
:Rich
:
:
Regarding the article on seleniums....don't believe everything you read on the net. If more people understood how seleniums work they wouldn't publish articles like this.

As long as your filters are new the seleniums will last a long time. The only failed seleniums I have seen in radios have been because of bad electrolytics.

:::Ok so i have some sets that i use pretty frequently, and i am afraid of the dreaded rectifier failure i have heard so much about, but i am somewhat lacking in cash to send these radios across the world to get fixd, so i was wondering if someone could help me out or walk me through the process.... the models are as follows: 1) zenith k731 2) zenith hifi h840 3) a zenith chassis from the 40s, not sure of model number, and a small plastic am/fm zenith set. these are my babys any help would be so appreciated, i know basic soldering but am pretty new to all of this, i just know i love these radios =) thanks so much and best regards
:::
::
::
::Bjorn...
::
::there are lots of pros and cons about changing selenium.
::
::It relatively easy to do.
::
::http://www.w3hwj.com/index_files/RBSelenium2.pdf
::
::I hope this helps.
::
::Rich
::
::
:Regarding the article on seleniums....don't believe everything you read on the net. If more people understood how seleniums work they wouldn't publish articles like this.
:
:As long as your filters are new the seleniums will last a long time. The only failed seleniums I have seen in radios have been because of bad electrolytics.
:
Lewis

:::Ok so i have some sets that i use pretty frequently, and i am afraid of the dreaded rectifier failure i have heard so much about, but i am somewhat lacking in cash to send these radios across the world to get fixd, so i was wondering if someone could help me out or walk me through the process.... the models are as follows: 1) zenith k731 2) zenith hifi h840 3) a zenith chassis from the 40s, not sure of model number, and a small plastic am/fm zenith set. these are my babys any help would be so appreciated, i know basic soldering but am pretty new to all of this, i just know i love these radios =) thanks so much and best regards
:::
::
::
::Bjorn...
::
::there are lots of pros and cons about changing selenium.
::
::It relatively easy to do.
::
::http://www.w3hwj.com/index_files/RBSelenium2.pdf
::
::I hope this helps.
::
::Rich
::
::
:Regarding the article on seleniums....don't believe everything you read on the net. If more people understood how seleniums work they wouldn't publish articles like this.
:
:As long as your filters are new the seleniums will last a long time. The only failed seleniums I have seen in radios have been because of bad electrolytics.
:
Lewis

::::Ok so i have some sets that i use pretty frequently, and i am afraid of the dreaded rectifier failure i have heard so much about, but i am somewhat lacking in cash to send these radios across the world to get fixd, so i was wondering if someone could help me out or walk me through the process.... the models are as follows: 1) zenith k731 2) zenith hifi h840 3) a zenith chassis from the 40s, not sure of model number, and a small plastic am/fm zenith set. these are my babys any help would be so appreciated, i know basic soldering but am pretty new to all of this, i just know i love these radios =) thanks so much and best regards
::::
:::
:::
:::Bjorn...
:::
:::there are lots of pros and cons about changing selenium.
:::
:::It relatively easy to do.
:::
:::http://www.w3hwj.com/index_files/RBSelenium2.pdf
:::
:::I hope this helps.
:::
:::Rich
:::
:::
::Regarding the article on seleniums....don't believe everything you read on the net. If more people understood how seleniums work they wouldn't publish articles like this.
::
::As long as your filters are new the seleniums will last a long time. The only failed seleniums I have seen in radios have been because of bad electrolytics.
::
:
:
:
:Seleniums do age and get weaker with use. If your B+ is low, it is time for a replacement.
:Lewis
:

Transistors use pn junctions and don't deteriorate with use. Seleniums use an oxide coating on metal plates. The forward drop and internal resistance tends to increase with age. This increases heat dissipation which speeeds up the process. They gradually fail. Low current drain useage extends life. The way to determine replacement time is to measure the forward drop. The quick way is to check the B+. If its low, the rectifier is suspect. The big ones mentioned also deteriorate but their capacity is so much more than the small ones that they can be used much longer.

This brings up another point about selenium rectifier replacement. There is a fallacy that the series resistor always needs to be increased to drop the B+ when replacing a selenium with a diode. This is only true if the selenium is as part of a filament supply or some other critical voltage derived directly from it. For B+ only the increase will be unimportant. A new selenium has forward drop of about 0.8 volts per plate. A typical set uses one of six or seven plates, giving a forward drop of 4.8 to 5.6 volts. An aged selenium may have a drop of 1.5 volts per plate. In either case the increase in B+ will be no more that about 10 volts. This is not a problem for tube stuff where +/-20% tolerances are common.

:That is like saying a transistor gets weaker with age. A selenium is a solid state device, just like a transistor.If they are not physically damaged they are as good as the day they were made. There are many seleniums over forty years old in welders and plating shops that are still working fine.
:

:Transistors use pn junctions and don't deteriorate with use. Seleniums use an oxide coating on metal plates. The forward drop and internal resistance tends to increase with age. This increases heat dissipation which speeeds up the process. They gradually fail. Low current drain useage extends life. The way to determine replacement time is to measure the forward drop. The quick way is to check the B+. If its low, the rectifier is suspect. The big ones mentioned also deteriorate but their capacity is so much more than the small ones that they can be used much longer.
:
:This brings up another point about selenium rectifier replacement. There is a fallacy that the series resistor always needs to be increased to drop the B+ when replacing a selenium with a diode. This is only true if the selenium is as part of a filament supply or some other critical voltage derived directly from it. For B+ only the increase will be unimportant. A new selenium has forward drop of about 0.8 volts per plate. A typical set uses one of six or seven plates, giving a forward drop of 4.8 to 5.6 volts. An aged selenium may have a drop of 1.5 volts per plate. In either case the increase in B+ will be no more that about 10 volts. This is not a problem for tube stuff where +/-20% tolerances are common.
:
::That is like saying a transistor gets weaker with age. A selenium is a solid state device, just like a transistor.If they are not physically damaged they are as good as the day they were made. There are many seleniums over forty years old in welders and plating shops that are still working fine.
::
:

No mention was made of eliminating the series resistor, only that there was no need to increase its value. The resistor is there to limit inrush current.

Selenium rectifiers were a good first start at solid state rectifiers. The fact is they deteriorate with age. In other words, they wear out. Yes there are still special applications but these are few. Technology moved on, that's why they were only used for a short time.

As for replacement, you are correct in that if they do not show excessive forward drop there is no need to rush to change them for a diode. Most of mine are still in place but I get rid of them if I do a repair for someone else.

As a side note, if you want to test them in circuit, this can be done with a peak indicating voltmeter. This is simply a peak detector connected to a DVM (10 meg in) or VTVM. This can be made up of a 1N4007 and an 0.047 cap. Connect the series combination across the rectifier and connect the DVM across the cap. The arrow end of the diode goes toward the ac source. This will read the forward drop less about 0.6 volts. If it is more than about 1.2 volts per plate, the selenium is on the way out. The forward drop for the typical radio selenium was about 5 to 7 volts when new.

A peak-to-peak meter doesn't work, I suspect you know why.

:A current limiting resistor is always required when replacing a selenium with a silicon diode. A silicon diode will not limit current, a selenium will.
:
:And remember, a silicon diode is susceptible to transient voltage spikes and will fail shorted, destroying electrolytics and tube filaments.
:
:It is not surprising the selenium has such a bad reputation, it was used in televisions in a voltage doubling power supply which over stressed the electrolytics causing them to fail, and in turn causing the seleniums to fail. I replaced many hundreds of failed seleniums in TV's with silicon diodes. So if you have a TV I recommend replacing the seleniums, but I would never replace them in a radio.
:
:
:
:
:

There was also a copper oxide rectifier. It had a lot of shortcomings, also. They were used more in commercial applications. They were easily replaced with silicon, too.
Lewis

:
:
:There was also a copper oxide rectifier. It had a lot of shortcomings, also. They were used more in commercial applications. They were easily replaced with silicon, too.
:Lewis
:

::
::
::There was also a copper oxide rectifier. It had a lot of shortcomings, also. They were used more in commercial applications. They were easily replaced with silicon, too.
::Lewis
::
:
:Lewis, I suggest you do some research. Copper Oxide rectifiers were used in low power applications such as tube testers and test meters (many of these testers are still in use today). And contrary to what you stated they cannot be easily replaced with silicon due to the large voltage drop in the silicon.
:
:I think I will let this subject drop, it is simply amazing how many people can be misled by a few incorrect, undocumented articles on the net.
:
Well, Dave, I will let this subject drop, too, but I worked at AT&T for a few years, and we were replacing copper oxide with silicon on a daily basis. I only know what I did for a living.
Lewis

:Transistors use pn junctions and don't deteriorate with use. Seleniums use an oxide coating on metal plates. The forward drop and internal resistance tends to increase with age. This increases heat dissipation which speeeds up the process. They gradually fail. Low current drain useage extends life. The way to determine replacement time is to measure the forward drop. The quick way is to check the B+. If its low, the rectifier is suspect. The big ones mentioned also deteriorate but their capacity is so much more than the small ones that they can be used much longer.
:
:This brings up another point about selenium rectifier replacement. There is a fallacy that the series resistor always needs to be increased to drop the B+ when replacing a selenium with a diode. This is only true if the selenium is as part of a filament supply or some other critical voltage derived directly from it. For B+ only the increase will be unimportant. A new selenium has forward drop of about 0.8 volts per plate. A typical set uses one of six or seven plates, giving a forward drop of 4.8 to 5.6 volts. An aged selenium may have a drop of 1.5 volts per plate. In either case the increase in B+ will be no more that about 10 volts. This is not a problem for tube stuff where +/-20% tolerances are common.
:
::That is like saying a transistor gets weaker with age. A selenium is a solid state device, just like a transistor.If they are not physically damaged they are as good as the day they were made. There are many seleniums over forty years old in welders and plating shops that are still working fine.
::
:
Hi Edgar,

The fallacy you point out is really true. You are in error. I know this by experience.
If a selenium is replaced and the dropping resistor left alone, all the voltages will be high because the forward drop of the selenium is no longer present.
I made this mistake in a radio and the first electrolytic was eventually destroyed because of this.

Seleniums have fins to dissipate significant energy caused by their voltage drop. Silicone diodes do not need the fins because their voltage drop is so much lower. That energy that had been burned in the selenium now needs to be burned in a larger resistor.

Best Regards,

Bill Grimm

The volatge is only higher by the difference in forward drop. That will only be about 10 volts max, unless the selenium was well on the way to failing completely. That's what was stated.

If your caps blew they were ready to fail and should have been replaced when the rectifier was changed. If they were new and failed, they were defective. The resistor is there to limit inrush current not to protect the filter caps from over voltage.

: The fallacy you point out is really true. You are in error. I know this by experience.
: If a selenium is replaced and the dropping resistor left alone, all the voltages will be high because the forward drop of the selenium is no longer present.
: I made this mistake in a radio and the first electrolytic was eventually destroyed because of this.
:
: Seleniums have fins to dissipate significant energy caused by their voltage drop. Silicone diodes do not need the fins because their voltage drop is so much lower. That energy that had been burned in the selenium now needs to be burned in a larger resistor.
:
:Best Regards,
:
:Bill Grimm
:
:

Hi Edgar,
Your mistake is that you think that only the resistor limits inrush. It is the resistor and the selenium that limit.

When you jump into print claiming that the resistor does not have to be increased you do a diservice since that is wrong.

Best Regards,

Bill Grimm

The described technique has been used dozens of times over several years with zero problems. Your arguments show a lack of understanding. Research can cure this.

:Hi Edgar,
: Your mistake is that you think that only the resistor limits inrush. It is the resistor and the selenium that limit.
:
: When you jump into print claiming that the resistor does not have to be increased you do a diservice since that is wrong.
:
:Best Regards,
:
:Bill Grimm
:

The described technique has been used dozens of times over several years with zero problems. Your arguments show a lack of understanding. Research can cure this.

:Hi Edgar,
: Your mistake is that you think that only the resistor limits inrush. It is the resistor and the selenium that limit.
:
: When you jump into print claiming that the resistor does not have to be increased you do a diservice since that is wrong.
:
:Best Regards,
:
:Bill Grimm
:

It's Friday night. You gentlemen should be out having margaritas, not bickering in here.

T.

Analysis is the answer.

:It's Friday night. You gentlemen should be out having margaritas, not bickering in here.
:
:T.
:

T,
Had a blow-out on my flip-flops and can't go out. Any suggestions other than my resident Merlot?

marv

:It's Friday night. You gentlemen should be out having margaritas, not bickering in here.
:
:T.
:

It would do well to anal-ize the whole topic.

Wow. What an intelligent response.

:It would do well to anal-ize the whole topic.
: