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Selenium Rectifier Replacement - Printable Version

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Selenium Rectifier Replacement - Joe Rossi - 02-15-2015

I am gathering parts for a little Zenith L403 ac/dc radio from the early '50's.  It has a selenium rectifier (Zenith p/n 212-5), and says it's rated for 75 ma, no more info.  Will a 1N4007 be able to replace that?  Should I even replace it at all?  Anyone have a suggested replacement?  Thanks!

RE: Selenium Rectifier Replacement - morzh - 02-15-2015

You could test it, it is after all a semiconductor rect bridge, nothing more.
Otherwise, yes, 1N4007 are good, not sure if you need to account for voltage drop, if you do, a resistor in series will do.

RE: Selenium Rectifier Replacement - Joe Rossi - 02-15-2015

(02-15-2015, 05:14 PM)morzh Wrote:  You could test it, it is after all a semiconductor rect bridge, nothing more.
Otherwise, yes, 1N4007 are good, not sure if you need to account for voltage drop, if you do, a resistor in series will do.

I knew that YOU would have the answer for me.  Thank you friend!

RE: Selenium Rectifier Replacement - Paul Philco322 - 02-15-2015

When those Selenium Rectifiers fail they get very hot and really let off a stink. I would replace it, then you can enjoy without worry.

Paul

RE: Selenium Rectifier Replacement - morzh - 02-15-2015

Name me one eectronic component whose magic smoke smell like petunias Icon_smile Icon_smile

RE: Selenium Rectifier Replacement - Joe Rossi - 02-15-2015

(02-15-2015, 08:09 PM)Paul Philco322 Wrote:  When those Selenium Rectifiers fail they get very hot and really let off a stink. I would replace it, then you can enjoy without worry.

Paul

Thanks Paul.  Parts are on order and I finally did locate a source that states a 3W 300 to 330 ohm resister in series to make up for the voltage drop.  Joe

RE: Selenium Rectifier Replacement - Paul Philco322 - 02-15-2015

I have a red one of those lil Zeniths.

Paul

RE: Selenium Rectifier Replacement - Eric Adams - 02-15-2015

I've done quite a few Zeniths with the rectifier. I use either a 5W 100 or 150 ohm resistor in series and I've never had a problem.

RE: Selenium Rectifier Replacement - Joe Rossi - 02-16-2015

Paul,  Mine is a grayish-white, belonged to my Aunt.

Eric,  Once it is recapped, I'm going to measure the voltage off the rectifier, put in the 1N4007 and play with resister values.   Thanks for the tip!

RE: Selenium Rectifier Replacement - codefox1 - 02-17-2015

Voltage increase is usually insignificant in AC/DC 5 or 6 tube sets. I'd add a 22 ohm 1/2 watt or 1 watt fusister or better yet a proper fuse to the set.

RE: Selenium Rectifier Replacement - Joe Rossi - 02-17-2015

(02-17-2015, 09:58 AM)codefox1 Wrote:  Voltage increase is usually insignificant in AC/DC 5 or 6 tube sets.  I'd add a 22 ohm 1/2 watt or 1 watt fusister or better yet a proper fuse to the set.

Only 4 tubes in this radio, three 1 volt and one 3 volt.

RE: Selenium Rectifier Replacement - Arran - 02-17-2015

(02-17-2015, 05:13 PM)Joe Rossi Wrote:  
(02-17-2015, 09:58 AM)codefox1 Wrote:  Voltage increase is usually insignificant in AC/DC 5 or 6 tube sets.  I'd add a 22 ohm 1/2 watt or 1 watt fusister or better yet a proper fuse to the set.

Only 4 tubes in this radio, three 1 volt and one 3 volt.

No, you need to calculate the proper size resistor in this case, it is much more critical then in a regular AC radio. Each tube needs 1.4 volts, not 1 volt, and the 3 volt one is actually 2.8 volts, too low and the set won't work properly, too high and the tubes burn out prematurely, so 7 volts ideally. If the original selenium rectifier is still working do some voltage measurements to see what the output voltage is before it gets to the filament dropping resistor, and after it.
Regards
Arran

RE: Selenium Rectifier Replacement - morzh - 02-18-2015

I lost you guys, it looks now as if you are talking of filament voltages, but then what does the rectifier and the resistor have to do with it?

RE: Selenium Rectifier Replacement - Joe Rossi - 02-18-2015

(02-17-2015, 11:38 PM)Arran Wrote:  
(02-17-2015, 05:13 PM)Joe Rossi Wrote:  
(02-17-2015, 09:58 AM)codefox1 Wrote:  Voltage increase is usually insignificant in AC/DC 5 or 6 tube sets.  I'd add a 22 ohm 1/2 watt or 1 watt fusister or better yet a proper fuse to the set.

Only 4 tubes in this radio, three 1 volt and one 3 volt.

No, you need to calculate the proper size resistor in this case, it is much more critical then in a regular AC radio. Each tube needs 1.4 volts, not 1 volt, and the 3 volt one is actually 2.8 volts, too low and the set won't work properly, too high and the tubes burn out prematurely, so 7 volts ideally. If the original selenium rectifier is still working do some voltage measurements to see what the output voltage is before it gets to the filament dropping resistor, and after it.
Regards
Arran

Thanks Arran.  I was aware that the filament voltages are 1.4 and 2.8 volts. I referenced them that way to indicate that the set only has 4 tubes a 1R5, 1U4, 1U5, and a 3V4, and atypical to some of the older 5+ tube AC/DC sets.  There is already a 180 ohm 4W and 1750 ohm 5 watt just north of the rectifier.  I want to be sure that in replacing it I have the proper voltage between SE1 and  R13.   Thanks again, input is always appreciated!  Joe 

RE: Selenium Rectifier Replacement - codefox1 - 02-22-2015

Sorry for possibly misleading anyone, (should have looked at schematic before typing,) and agree that in an AC/DC/BATTERY set, the end of the voltage divider feeds the filament string, and it is VERY important to do whatever is needed to get that final voltage correct. Even before restoration sometimes the filament voltage is too high with today's line voltage and an increase in the first an last resistor in the chain can correct the situation. This is doubly important when replacing a blown 117Z3 or equivalent in similar sets.