In a valve Dansette Bermuda of early 60s Been in a loft for years. The mains wiring is perished and other wiring looks dodgy so testing some things cold first. Using 9V battery and 300 ohm dropper shows near enough 9V over the rectifier, how high V do you have to go with a good one to check it ? Are there safety grounds anyway for changing to a 1N4007 or so ? Single element rectifier Siemens lazy S logo Made in Germany
2250c50 Kc 0.6e 11/16
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
If you want to listen to the radio, there are lots better ways to do it.
OLD radios have emotional and monetary value just because they're old. I never understood why people pay huge bux for something just because it's old..."Hey, look at me, I just paid big bux for a radio that sounds like crap!! But I got one of only 1000 in existence. Ain't I cool?"...but I digress...
I suggest that both the emotional and monetary value of an old thing is a strong function of it's "stockness". Stated another way, the less stuff you change, the more value it has. Stated another way, "If it ain't broke, don't fix it."
Put your effort into forming the caps before you plug it in.
Yes. The original selenium rectifier has a rather substantial forward voltage drop. The design of the filters and the rest of the receiver take this into consideration. When you replace it with a 1N4007, the forward voltage drop will be MUCH less. Chances are good that you'll apply too much voltage to the filter caps and receiver.
If you're going to simulate a selenium rectifier, you'll probably need to add a series resistor to drop the voltage somewhat.
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Also, watch out for dead electrolytic filter capacitors. They will need to be "reformed":
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Jeff Liebermann jeffl@cruzio.com
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I would look at the working voltage rating of the original electrolytics and make sure that the voltage which you apply with the new silicon diode does not exceed 85 percent of it. Use a variac to do this. It will also reform the electrolytics at the same time. But a a previous posted said if the selenium unit is ok then I wouldn't bother to replace it. Lenny Stein Barlen Electronics.
Well you may not agree with it, but it's certainly a common human thing to do. People pay big bucks for things a lot less useful than an old radio, one needs only to walk past a jewelry store to observe this. Diamonds are good for cutting things, that's my view, but obviously a whole lot of people disagree with me.
That said, there's just nothing quite like listening to an old radio, definitely an emotional component to it, my '37 Zenith console is the only radio I ever listen to.
Ask in rec.antiques.radio+phono...or just google the subject in that forum. It's been discussed at length. The general outcome is that yes, you should replace the selenium with silicon. It's prone to self destruct, and if it does, it emits nasty--some say toxic--fumes. (IOW the magic smoke contained therein can harm you.)
There is a greater voltage drop across selenium. A series resister should be added to compensate, calculated according to average B+ voltage/current.
The owner likes the smell contained within, on lifting the lid. Taking it apart it is even stronger old radio smell. Does the selenium rectifier add to the smell in any way ? so replacing it would "lessen the experience" ?
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
I take my iPod jogging, I listen to CDs in the car, the content on either is far superior, but it's not the same experience as sitting by the fire near the warm glow of a classic radio. It's not about the content or the sound quality.
Mpffff... let's try to answer the question, at least a little bit.
a) The OEM selenium diode is prone to failure. When it fails it does so in a spectacular manner such that you will offend any and all parties within smell-range and at the same time release fumes that are toxic (but by no means as toxic as they smell). So: Get rid of it. Better yet, leave it in place for appearance but hide the new silicon diode behind it.
b) There is a significant voltage-drop across the diode. In battery sets (typically with 1.4V tubes, not accounting for this drop can either greatly shorten tube life *or* blow filaments altogether.
c) As selenium diodes age, they increase in resistance. Many battery sets (with specific reference to the post-war, miniature-tube Zenith TransOceanic series) will fail due to too-low filament voltage from this cause. On the other hand, with some of their mains-only radios, with specific reference to the post-war AM/FM units, this is not a major issue.
So: Yes, replace the diode. Add a resistor in series to get the proper filament voltage if this is a concern. For the T/O series, that can work out somewhere between 30 and 80 ohms @ 2 watts (use 5 if you can) or better. Such a resistor is harder to conceal than the diode, but it does make the radio functional with reasonable safety. But if the down- line components from the rectifier are not voltage-sensitive, you may not have to add the dropping resistor.
Now, keep in mind that if you are replacing a single selenium diode (i.e.: NOT a stack), the forward voltage drop is insignificant such that no additional resistor is required. Or, you can put a zener diode across the filament string (if so equipped), to protect the tubes.
I picked up a pair of Dynaco Monoblock amplifiers at a garage sale. Hooked 'em up and couldn't tell that they sounded any different. Definitely winter weather amplifiers. Coulda roasted wieners on 'em. Luckily, I found someone who thought they did sound better and offered me 10x what I paid for them. Out they went. I live in a no-nostalgia zone. ;-)
Take another look at the number. Might it be "B250C50"? Many European rectifiers used to give you the voltage (B, in this case 250 volts) and current rating (C, in this case 50mA) of the device.
I agree with the other posters that you can replace the selenium with a silicon diode, but may need to ad a dropping resistor as the B+ may be higher because of less loss in the rectifier. I usually bring the item up slowly on a variac and make sure that I don't exceed the voltage of the filter caps. Better still if you have a factory diagram telling you what the B+ is supposed to be. Then you can choose an appropriate resistor, and you might need quite a few watts worth too.
Unfortunately, I can't suggest how you might test the selenium.
There isn't realy any reason to test them. Given how nasty it is when they fail, and how likely that is to occur, I replace them any time I encounter them.
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