Replace Selenium rectifier with silicon diodes
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- Опубликовано: 4 окт 2024
- Tube radios from the 50s often have selenium rectifiers in the power supply, which may need to be replaced, preferably with a silicon diode bridge. This is the case here. I take you through my way of 're-stuffing' a selenium rectifier on a SABA Freiburg W2 with 4 silicon diodes.
This radio is the object of a series of videos on its restoration, which you can see here:
• Saba Freiburg W2 Resto...
You can also watch how I re-stuff the electrolytic filter capacitors of this radio here:
• Re-stuffing filter cap...
Enjoy, and comment if you so desire.
Speaking of unsightly results, why not open the side folds by tapping a long knife blade into the joint? No stretching, no tool marks and a perfect close at the end.
I would keep the Se rectifier in place. Solder wires on to it, but hide them where they won't scratch or short anything. Keep the nostalgic look.
Enjoyed this one. A wide flat (about 20-25mm) SMOOTHED EDGES chisel (engineers or joiners type) would be very useful for opening the metal case. This would be introduced in a similar place to where you used the screwdriver, but instead of twisting the chisel, you'd mallet it into the semi-rolled joint, a little at a time whilst moving along the joint length, until the joint had been opened by essentially bending out the lower bend of the casing, and to a lesser extent the top bend. And unless you're a sheet-metal worker, when closing the joint, use a piece of 20x40mm timber as a punch/spoon, either longitudinally or broad-side, to seal up the joint. This same piece of wood could also be used as a punch to open the joint, in a similar manner to that described for using the metal chisels, above. Hope this may be useful to some of you.
I certainly have to do a neater job of opening the cans. Thanks for the tips.
Thank you sir. A big help for me with replacing mine!
Pleasure
Microwave rectifier for voltage drop.
I haven't tried this yet but it occurred to me that it would be more efficient to install one or two microwave rectifier diodes in series with the silicone replacement bridge to handle the appropriate voltage drop. Those diodes are multiple diodes in series to handle the HV they're rectifying. They also handle a fair amount of current.
You can forward bias the diode and check the drop by inserting a 9V battery in series with your voltmeter.
They have about 3 volts drop.
So, just insert the appropriate number of microwave rect diodes in series with your bridge rect and voila! Instant voltage drop with minimum heat produced.
Any ideas on why this might be a problem are welcome.
NOTE:You'll have to buy the entire microwave oven at a thrift store as the appliance industry has decided these diodes are precious and want like $50+ each for these!
Got to try it sometime.
Excellent vid, thank you. I was going to just ditch the whole piece but now I think I'll stuff it like you've done here! Since the silicon diodes will bump the voltage up a good amount, do you ever add series resistance? I've also seen people say you have to strap caps across each diode, and also a KV cap across the secondary.
I add a series resistor if the voltage needs a little taming. You can add the caps to clean out switching noise.
Thanks for another great video. Just one question, I’ve watched a number of videos and in some it only shows a single 1N4007 diode in series with a resistor to replace the selenium rectifier. In your video you use 4 diodes. Is either way satisfactory? I have a 1959 Schaub Lorenz valve radio, my selenium rectifier is physically quite small.
BK Gold Detecting : the single diode is used when replacing a half-wave selenium rectifier. In this case it’s a selenium full-wave bridge rectifier so the four diodes are used. See what yours is and replace accordingly.
Wow you have no idea how helpful this is!! Can you suggest what diode values to use for 220v 150ma?
1N4007 is good.
Hi. Can you help me with an advice please? Or anyone else? I got Nordmende Elektra tubes radio 1959. The selenium rectifier stinks when gets hot. I've done a silicone rectifier with a resistor in series with the +, but the problem is with the silicone rectifier I've done, I got output voltage on it of 300-305 volts with speaker's buzzing noise. With the original selenium rectifier I got output on it 190-195 volts, no buzzing noise on speaker. Any advice how can I drop down the voltage on silicone rectifier from 300v to 190v? Thanks anyone in advance.
You must get a schematic. The 300v is closer to the correct voltage than the 190. However, playing with 300v without experience is asking for trouble.
@@electronicsoldandnew Thanks very much for swift reply. I found out on schematic that the original rectifier output must be 260 volts. Although, the radio works perfectly with original selenium rectifier even its output voltage is 190, no buzzing noise on speaker with the volume completely down, but the problem with this rectifier is that smells bad and gets very hot. With the silicone diodes rectifier I've done, its output voltage is 300 volts, radio works perfectly too, but little buzzing noise on the speaker when the volume completely down. I have to find out how to drop down the voltage from 300v to 260v. 1st of all I don't want to damage the radio due higher voltage. 2nd of all, the small buzzing noise it's something that scratch my brain because something doesn't work as should. Thanks again for your kindness to reply. All the best!
Brilliant video. I am replacing a selenium rectifier on a Vadis Escort tube guitar amplifier. My question is this - what value capacitors/resistor should I use in the new power supply circuit? The present values for the caps are 24uF 350V and the resistor, which is burnt out I think is 10ohm? 10Meg? Can't quite see as it's burnt out. Appreciate your help. Thanks.
i’m not sure I can answer you accurately, because I don’t know the actual circuit. However, 24 µF capacitor sounds about right, and having replaced it with diodes, you can probably change that to 47 µF without any problem and a little bit more filtering. The resistor, if it’s in series with a B+ will probably be a low value, definitely not one 1M.
@@electronicsoldandnew So I did all that and powered the amp on. It has a hum that sounds like a half wave rectified circuit. I should have mentioned when I changed out the selenium rectifier, the filtering section was a Pi filter with two Capacitors in series with the small value resistor going to ground. Should I now change the filtering circuit to get rid of that oscillating hum?
Thanks for your help.
You should add (just as you suggested later on) as resistor in series as selenium rectifiers have quite a high resistance when new, as they get older they typically increase in resistance.
What is your opinion on modifying the transformer to lower the output voltage for use with modern rectifier diodes. I have a Nordmende radio (uses selenium rectifier so no center tapped secondary) that I am restoring and looking at the power transformer I noticed that the outermost layer of winding was from the secondary. So I went and unwound approximately 80 turns out of the 1280 total turns of the secondary. Measured the rectified output afterwards and it was down 25V from the original. Then moved the input tap from 220V to 240V and got the rectified voltage down another 20V (I have 230V in my wall outlet in Romania). So the voltage I get now is very close to spec without using a resistor. The transformer operating temperature seems to be the same as before. Will change the mains fuse to the lowest amperage rating possible just for peace of mind.. Do you think this is a safe modification? Thank you!
+Gherghinescu George : I think it is quite safe, but a little risky as you can damage the transformer if you're unlucky. The secondary is often on the outside, but unwinding turns to reduce the voltage, although technically the right thing to do, can be very difficult in some transformers. I'm glad you did it successfully. Good luck with your project.
Gherghinescu George It sounds like a lot of extra work to me...