Selenium rectifier testing ?
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From: Ron(UK) on 19 Nov 2007 14:41 N Cook wrote: > Does the selenium rectifier add to the smell in any way ? They certainly do when they fail! Ron(UK)
From: James Sweet on 19 Nov 2007 14:55 > Post a picture of the rig you use to take that zenith jogging. > > I agree, I just don't practice. > > I can think of only one old thing that I wish I still had...nope, > I really don't want her back either... ;-) > > Out with the old, in with the fully depreciated... > 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.
From: pfjw on 19 Nov 2007 15:37 On Nov 19, 9:57 am, "N Cook" <diver...(a)gazeta.pl> wrote: > 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 onhttp://home.graffiti.net/diverse:graffiti.net/ 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. Peter Wieck Wyncote, PA
From: mike on 19 Nov 2007 20:21 James Sweet wrote: >> Post a picture of the rig you use to take that zenith jogging. >> >> I agree, I just don't practice. >> >> I can think of only one old thing that I wish I still had...nope, >> I really don't want her back either... ;-) >> >> Out with the old, in with the fully depreciated... >> > > > 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. > > 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. ;-) -- Return address is VALID!
From: Tim Schwartz on 20 Nov 2007 08:40 N Cook wrote: > 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 > http://home.graffiti.net/diverse:graffiti.net/ > > > Nigel, 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. Regards, Tim Schwartz Bristol Electronics
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