I like your reasoning and testing the voltage half way through the circuit seems like the best approach. Excellent discussion.

Thanks for all of your hard work putting these videos together. They are very helpful. Hope you are well, Richard.

An oldie but a goodie. This answered my questions as I am about to replace a selenium rectifier myself in my first radio restoration. I have, however, opted to use a 25 watt 100 ohm potentiometer instead of a pile of discrete resistors to arrive at the proper resistance. With it I can set the pot for maximum resistance, jumper it into the circuit, bring the radio to full operating voltage and then adjust the pot until the filament voltage is at the proper value. I then simply measure its resistance and solder in a suitable single value replacement.

Fantastic explanation. Your videos are short, precise and to the point. Thank you.

Rick, As you had emailed me last week. I will use this variac technique to help determine the resistance needed to suppliment the replacement electrodynamic speaker's field coil being700 ohms less DC resistance than the original schematic calls for. It's a simple yet powerful method! Thanks!

Rick... Great instructional video. You break everything down to an understandable lesson. Thank You. Ron in Putnam, Tx

I have several portable tube radios all seem to work ,but if I have to get rid of my selenium rectifier ,this video will be something that will be handy as hell ,thank you for this video and explaining it so well .

Superb presentation, narration and diagrams, and very thorough. I am going to view more of your videos. Thanks!

Very informative video. Nice Variac power supply you have there. I've been wanting to build one of those for a while.

Perfect Rick, your the man! I check voltage on the radio I bought with the selenium bypassed with a 1N4004. Some one else did it, with out a drop down resistor. The Spec voltage past the rectifier and stock 22ohm R is 128V. I was at about 144V (+16V). The Plate was 119V, +9V (spec 110v). Measuring voltage drop across stock 22ohm R, some basic ohms law math, the ideal resistor is about 100ohm! Don't have room for 10W in stock location, which is only 1W. I'll go 3-5W.

Rick the clairvoyant, Don't know how you do it, but once again your timing is perfect. I just finished reading about selenium rectifiers and will soon be replacing one in the wife's AM/FM. Figuring out how to determine the resistor value had me a bit stymied. But not any longer. I'll bet tomorrow something else will pop up that I need to know about. and in a few days you'll post a vid with the answers. Maybe I should take you to Vegas. :) Regards, John.

Thanks Ron, I just found my electrolytic capacitors for the next project. So it's time to start working on it, taking pictures and making drawings. Rick

I've only had to do one set with the selenium rectifier (a zenith AM/FM tabletop) and was just told to use a 50 Ohm 10 W resistor. I knew there was a proper way to do it, thanks a bunch!

Thanks CameramanLink Your welcome, and I'm glad you found it useful.

It is surprising how useful an isolation transformer and a variac are. I use them all the time. It makes a lot of difficult decisions easer and more accurate. It also makes the work safer for the user and there is much less chance of doing damage to the unit under test. Thanks.

I love your videos they are helpful ,thanks.I do watch more than once,I am sure a lot of us do

Very similar to my Philco E670-124. I am going to replace the selenium in it soon. Cool video!

thanks for the video's , I've learned alot

Good information and instruction, thank you!

Thank you. I appreciate your help. I feel dumb. I see its a half wave rectification. It is just so crude (ha ha) it's throwing me. In tube audio amps I built, I used a power transformer and regulated DC power for the filaments. I see they made some compromises to make the radio AC/DC powered with out a transformer. I look forward to watching all your videos. I am sending you PM!

Thanks. There are/were many manufactures of selenium rectifiers of all types. So that and how it is used varies greatly. If your radio is not a tube portable, the procedure is the same except you would check the plate voltage of the audio output tube. I decided to us a tube portable because they are the most critical and if done wrong you will burn out some filaments.

Thanks! I hope it works. My machine is a Standard Buisness Machines Co. "magnascriber" model 160.

Excellent tip very helpful thanks again

Thanks for the video Rick! this really helps me a lot! only problem is I do not have a variac... is there a safe way to do this without one? I guess just start with a very high value resistor and work my way down.

On a non-battery set the filament supply is not supplied by the B+. The voltage to watch on the non-battery is the plate voltages. I use the audio output plate voltage as a check then when that is correct I check the other plate voltages. And you are right to start with a resistor to large and then work down. Thanks.

very well explained. 😎 Thank you.

And it is cheep too. I hope you enjoy the vids, and ask your questions.

I hope it helps! Thanks.

selinium rectifier semi stunk horrible when burning up

Thanks. It is also very accurate.

great info. i didn't know those rectifiers could go bad. I hear they smell something awful if they ever burn out.

Rich I am overhauling a Zenith Y832. The filament heaters are all AC and by pass the the selenium rectifier (diode). The current in-line resistor is 22ohm 1W. I am about to order all my new CAPS and wounder do I really need to put in a drop down resistor. The plates are rated for 100-250 volts. I don't think the difference will be that great. What do you think. I would rather replace the existing 22ohm with a larger one than add an additional one. Comment appreciated.

Thanks!

Hey John, If your radio is not a tube portable you just do the same thing but instead of the filament you check the plate voltage of the audio output tube. It has been a few years since I have been to Vegas, they'll probably let me in. Regards, Rick

Yep, need a substitute for the internal impedance of the tube. Thanks.

Correct. The voltage on your radio is AC and not supplied by the B+ power supply. For that type of radio the plate voltages need to be monitored as you try different series resistors.

Check the plate voltages. The plate voltage of the audio output tube should be close to the value of the B+ battery. If the selenium rectifier is bad, that variac will come in very handy. Let me know what the voltage read. You can also read the 1.5 volts across the filaments. If you have a 3V4 it may be 3V, if they wired it up with the center tap it may be 1.5V.

The selenium rectifiers I have replaced have had and internal resistance of 100-150 ohms. So I would remove the 22ohm and replace it with a 150ohm 10watt(if you have room) and then check all the plate voltages and the radios performance.

I looked up the diagram on Nostalgia Air and when the battery is used the AC is out of the circuit. As long as you use the right DC battery voltages you can test the radio with batteries. If you have more questions please email me. Good luck!

From what I have heard it a good idea to get rid of the selenium rectifier ,because if they go out they can cause a lot of damage,if it was mine I would want it out and replaced by a modern one .

oh also I do know that the first number in a tube type is usually the voltage, like 12AX7 is 12V and so on. this radio also has a 35C5, so I'm assuming the filiment voltage is 35V right?

If That Selenium rectifier is still working, measure the voltage across R8 which will give you by Ohms law the current through the rectifier. You can then calculate with the voltage drop across the se rectifier it's equivalent series resistance which you can then duplicate.

When you test for correct filament voltage, does it matter where the volume control is set or if a station is tuned in? Or would it not matter because you are only checking tube heater voltage? Thanks Rick!

PS the most critical tube is the audio driver a 35C5 which the specs say has Tung-Sol specs Max plate voltage 150V Max grid #2 voltage 130V For the same 35C5 tube GE specs Max plate voltage 135V Max screen voltage 117V Since line voltage is 117 I should be OK with the existing stock 22 ohm (1W) resistor down from the rectifier. Again the filament heaters are all AC.

Rick, can you test that radio with DC voltage by chance? I have a 600 T/O, no battery yet, but I was thinking of making one, thanks.

Ok perhaps a silly question when I put voltage into my selenium rectifier I see only DC voltage on the + side (or very little AC) .. If I put voltage into the diode.. I see both AC and DC coming out of the diode (at equivalent amounts).. what am I missing ?

I am confused? How can your replace a RECTIFIER with a single diode (plus drop down resistor)? I thought a rectifier is 4 diodes and a rectifies AC wave form to DC. (I know I am confused). Any one? Please straighten me out. I assume that the filaments are still AC and the diode just clips part of the wave? Totally lost. Thanks

Can you use resistors in place of the filaments' in order to check the voltage of the power coming in?

EXCELLENT!!!

I replaced a tube rectifier with a silicon diode, but didn't think about voltage drop. Maybe I should revisit this.

I just find the wiring diagram and I would alligator clip in a 150ohm in place of the 22ohm and check plat voltages and performance. If the voltage is low then I would try a 100ohm. Good luck.

The radio should play great!

Why not just measure the resistance of the selenium rectifier directly? Your method is much more elegant...I was just wondering.

What if you use 4 diodes in the same configuration as the selenium rectifier?

Why not use a variable 300 Ohm 2 watt resistor and bring it down until the filament voltage is correct? What am I missing here?

Thanks obbm2232

Do I need a resistor if I have a transformer Your radio looks like a hot chassi

I use a one or two amp diode, and that is wayoverkill

I figured you would know this. I hope it keeps someone from burning up some filaments. BTW I picked up some 78s last weekend. You sure are getting old._._._._.lol.

DC fed fIlaments?

Thanks. If it does go bad, depending on how, it can smell like rotten eggs.

I know it is confusing. I did a video called "Rectifiers, a few basics" 9 months also.

It would be more helpful to let us see you solder it in sometime schematics ,arent enough for us novice .it would make me better if I could at least see the repair.

Thanks cenzo188 I use the Variac in conjuction with isolation transformer with out fail. Those two items are a must for the workbench.