What I'd like to know is, how do you check a selenium rectifier to know if it's bad. All I see with it sitting on the bench is 2.4 megohm across it. Guy said it was working, he saw a puff of smoke and it died. I'm recapping the set now but I don't see anything that looks like it fried. Someone told me that a selenium rectifier will emit a puff of smoke when they die.
Should I see any kind of resistance or anything on a selenium rectifier? Can they be bench tested?
Thanks,
Johnny
:
:What I'd like to know is, how do you check a selenium rectifier to know if it's bad. All I see with it sitting on the bench is 2.4 megohm across it. Guy said it was working, he saw a puff of smoke and it died. I'm recapping the set now but I don't see anything that looks like it fried. Someone told me that a selenium rectifier will emit a puff of smoke when they die.
:
:Should I see any kind of resistance or anything on a selenium rectifier? Can they be bench tested?
:
:Thanks,
:Johnny
They have to be tested with a load at their working voltage, then you check the voltage drop across the selenium. The easiest way to check them is by checking the B+ after replacing the filter capacitors. Usually a set is designed for a resistor to go before the selenium does. A puff of smoke sounds more like a resistor, if the selenium went you would be complaining about the smell not the smoke.
I usually don't recommend replacing them 1N4007's in portable shortwave radios for many reasons, It is difficult to find the proper resistors to set the filament voltage, they create RF noise and need to be snubbed with a capacitor, when they go bad they short and fry lots of things including tubes, they have an instant on whereas a selenium has a soft start.
The has been much incorrect information on the net about seleniums, there is no documentation about anyone ever being harmed by the smoke from a selenium.
Seleniums last a long time and are still manufactured and used today.
All the TO's I repair have seleniums in them, if they were changed to silicon I put the seleniums back in.
The choice is yours
Dave
BTW is the specified 3-BX-671 schematic filling in adequately for your "7BX10" sets initial request, ::I'm working on an RCA 3-BX-671 that has a selenium rectifier in it. I've replaced it with a 1N4007 diode. I'm aware of the voltage checks I'll have to make and possibly adding a resistor if the voltage is too high. :
Sir Johnny. . . . .
Someone told me that a selenium rectifier will emit a puff of smoke when they die.
IF . . . . in a hard failure mode, (overload) or I have seen blistering of the paint on marginal overloading, OR just plain
FIREWORKS
when dumping into a quasi shorted condition of overloading , along with the fragrant, distinctive odor of selenium in the air.
Otherwise, its just a possible tapering off of performance with time, but they are quite hardy and long lived devices.
.
with both using the RCA RC-1125 chassis or its B version with the 50A1 being used.
So I am wondering if your unit is using the 50A1, as in their commonly shared Samuels 228-14, it is not filling in on the 50A1 info aspect.
BUT if your unit is not using that 50A1, it would be of no concern.
73's de Edd
::
::What I'd like to know is, how do you check a selenium rectifier to know if it's bad. All I see with it sitting on the bench is 2.4 megohm across it. Guy said it was working, he saw a puff of smoke and it died. I'm recapping the set now but I don't see anything that looks like it fried. Someone told me that a selenium rectifier will emit a puff of smoke when they die.
::
::Should I see any kind of resistance or anything on a selenium rectifier? Can they be bench tested?
::
::Thanks,
::Johnny
:
:
:They have to be tested with a load at their working voltage, then you check the voltage drop across the selenium. The easiest way to check them is by checking the B+ after replacing the filter capacitors. Usually a set is designed for a resistor to go before the selenium does. A puff of smoke sounds more like a resistor, if the selenium went you would be complaining about the smell not the smoke.
:
:I usually don't recommend replacing them 1N4007's in portable shortwave radios for many reasons, It is difficult to find the proper resistors to set the filament voltage, they create RF noise and need to be snubbed with a capacitor, when they go bad they short and fry lots of things including tubes, they have an instant on whereas a selenium has a soft start.
:
:The has been much incorrect information on the net about seleniums, there is no documentation about anyone ever being harmed by the smoke from a selenium.
:
:Seleniums last a long time and are still manufactured and used today.
:
:All the TO's I repair have seleniums in them, if they were changed to silicon I put the seleniums back in.
:
:The choice is yours
:
:Dave
:
Depending on where the electrolytic was, it could either cause hum or cause the set to just die. In a filament circuit of a portable radio, voltage might be reduced enough to just cause the radio to cut out, or in a voltage doubling circuit the voltage might drop out and cause the radio to die.
T.
I don't think I'm gonna dwell too awful much more on this puff. Get the set recapped, new 3V4 installed, 1N4007 is already installed, and then check to see what kind of voltage is coming out of the 1N4007 and make corrections with a series resistor if necessary.
If the set works great. If not then it's back to troubleshooting mode. The electronics in this set are in very good shape. Also no real build up of dust, dirt etc. It's pretty clean. Does have a broken dial cord that will get replaced last.
Johnny
:
:If a puff of smoke was noted, you should definitely look for a burned resistor or a blown electrolytic. Electrolytics that overheat from excessive leakage or incorrect voltage blow their seal and emit steam. You will find a small hole in the electrolytic rubber, and if you have a good capacitor analyzer, the electrolytic may show reduced capacitance and possibly leakage.
:
:Depending on where the electrolytic was, it could either cause hum or cause the set to just die. In a filament circuit of a portable radio, voltage might be reduced enough to just cause the radio to cut out, or in a voltage doubling circuit the voltage might drop out and cause the radio to die.
:
:T.
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:
:
:
: : : : : : : : : : : : :Sir Johnny. . . . . : : : :Someone told me that a selenium rectifier will emit a puff of smoke when they die. : : : :IF . . . . in a hard failure mode, (overload) or I have seen blistering of the paint on marginal overloading, OR just plain :FIREWORKS :when dumping into a quasi shorted condition of overloading , along with the fragrant, distinctive odor of selenium in the air. : : :Otherwise, its just a possible tapering off of performance with time, but they are quite hardy and long lived devices. :. : : : :BTW is the specified 3-BX-671 schematic filling in adequately for your "7BX10" sets initial request, :with both using the RCA RC-1125 chassis or its B version with the 50A1 being used. : : :So I am wondering if your unit is using the 50A1, as in their commonly shared Samuels 228-14, it is not filling in on the 50A1 info aspect. : : :BUT if your unit is not using that 50A1, it would be of no concern. : : : : : :73's de Edd : : : : |
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:::I'm working on an RCA 3-BX-671 that has a selenium rectifier in it. I've replaced it with a 1N4007 diode. I'm aware of the voltage checks I'll have to make and possibly adding a resistor if the voltage is too high.
:::
:::What I'd like to know is, how do you check a selenium rectifier to know if it's bad. All I see with it sitting on the bench is 2.4 megohm across it. Guy said it was working, he saw a puff of smoke and it died. I'm recapping the set now but I don't see anything that looks like it fried. Someone told me that a selenium rectifier will emit a puff of smoke when they die.
:::
:::Should I see any kind of resistance or anything on a selenium rectifier? Can they be bench tested?
:::
:::Thanks,
:::Johnny
::
::
:
::
::They have to be tested with a load at their working voltage, then you check the voltage drop across the selenium. The easiest way to check them is by checking the B+ after replacing the filter capacitors. Usually a set is designed for a resistor to go before the selenium does. A puff of smoke sounds more like a resistor, if the selenium went you would be complaining about the smell not the smoke.
::
::I usually don't recommend replacing them 1N4007's in portable shortwave radios for many reasons, It is difficult to find the proper resistors to set the filament voltage, they create RF noise and need to be snubbed with a capacitor, when they go bad they short and fry lots of things including tubes, they have an instant on whereas a selenium has a soft start.
::
::The has been much incorrect information on the net about seleniums, there is no documentation about anyone ever being harmed by the smoke from a selenium.
::
::Seleniums last a long time and are still manufactured and used today.
::
::All the TO's I repair have seleniums in them, if they were changed to silicon I put the seleniums back in.
::
::The choice is yours
::
::Dave
::
:
From the Hewlett Packard manual on the 450 Voltmeter:
http://www.hparchive.com/Manuals/HP-450A-Manual-SN-010.pdf
"4-2. The amplifier contains a selenium rectifier.
When selenium rectifiers burn out due to overheating,
poisonous fumes are released. Ventilate immediately,
and do not inhale these fumes. Do not handle the
rectifier until it has cooled."
I agree that catastrophic selenium rectifier failures aren't all that frequent. But you only need one to remember the smell! I used to work in a TV/Radio repair shop in the late 60s.
Rich
::I don't know where I came up with the 7BX10. I think the guy I got it from said that's what it was. It is definitely a 3-BX-671 and is not running a 50A1.
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::Sir Johnny. . . . .
::
::
::
::Someone told me that a selenium rectifier will emit a puff of smoke when they die.
::
::
::
::IF . . . . in a hard failure mode, (overload) or I have seen blistering of the paint on marginal overloading, OR just plain
::FIREWORKS
::when dumping into a quasi shorted condition of overloading , along with the fragrant, distinctive odor of selenium in the air.
::
::
::Otherwise, its just a possible tapering off of performance with time, but they are quite hardy and long lived devices.
::.
::
::
::
::BTW is the specified 3-BX-671 schematic filling in adequately for your "7BX10" sets initial request,
::with both using the RCA RC-1125 chassis or its B version with the 50A1 being used.
::
::
::So I am wondering if your unit is using the 50A1, as in their commonly shared Samuels 228-14, it is not filling in on the 50A1 info aspect.
::
::
::BUT if your unit is not using that 50A1, it would be of no concern.
::
::
::
::
::
::73's de Edd
::
::
::
::
::
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::
::::I'm working on an RCA 3-BX-671 that has a selenium rectifier in it. I've replaced it with a 1N4007 diode. I'm aware of the voltage checks I'll have to make and possibly adding a resistor if the voltage is too high.
::::
::::What I'd like to know is, how do you check a selenium rectifier to know if it's bad. All I see with it sitting on the bench is 2.4 megohm across it. Guy said it was working, he saw a puff of smoke and it died. I'm recapping the set now but I don't see anything that looks like it fried. Someone told me that a selenium rectifier will emit a puff of smoke when they die.
::::
::::Should I see any kind of resistance or anything on a selenium rectifier? Can they be bench tested?
::::
::::Thanks,
::::Johnny
:::
:::
::
:::
:::They have to be tested with a load at their working voltage, then you check the voltage drop across the selenium. The easiest way to check them is by checking the B+ after replacing the filter capacitors. Usually a set is designed for a resistor to go before the selenium does. A puff of smoke sounds more like a resistor, if the selenium went you would be complaining about the smell not the smoke.
:::
:::I usually don't recommend replacing them 1N4007's in portable shortwave radios for many reasons, It is difficult to find the proper resistors to set the filament voltage, they create RF noise and need to be snubbed with a capacitor, when they go bad they short and fry lots of things including tubes, they have an instant on whereas a selenium has a soft start.
:::
:::The has been much incorrect information on the net about seleniums, there is no documentation about anyone ever being harmed by the smoke from a selenium.
:::
:::Seleniums last a long time and are still manufactured and used today.
:::
:::All the TO's I repair have seleniums in them, if they were changed to silicon I put the seleniums back in.
:::
:::The choice is yours
:::
:::Dave
:::
::
:
:I'm working on an RCA 3-BX-671 that has a selenium rectifier in it. I've replaced it with a 1N4007 diode. I'm aware of the voltage checks I'll have to make and possibly adding a resistor if the voltage is too high.
:
:What I'd like to know is, how do you check a selenium rectifier to know if it's bad. All I see with it sitting on the bench is 2.4 megohm across it. Guy said it was working, he saw a puff of smoke and it died. I'm recapping the set now but I don't see anything that looks like it fried. Someone told me that a selenium rectifier will emit a puff of smoke when they die.
:
:Should I see any kind of resistance or anything on a selenium rectifier? Can they be bench tested?
:
:Thanks,
:Johnny
:
...Aside from that I had one selenium that became leaky. All it did was cause hum. Everything else I own that has a selenium rectifier is doing just fine.
A friend of mine had a Leslie rotary speaker amplifier that kept blowing fuses. All of the SILICON rectifiers had shorted. Nothing else was wrong with the amp. Replacement of the rectifiers cured the problem.
Do we really have to bring this up over and over again?
T.