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-   -   Can anyone help, identifing selenium bridge hookup please. (http://www.diyaudio.com/forums/tubes-valves/90126-can-anyone-help-identifing-selenium-bridge-hookup-please.html)

bembel 11th November 2006 03:43 PM

Can anyone help, identifing selenium bridge hookup please.
 
2 Attachment(s)
Here is a pict of the bridge rectifier, each block has 3 legs external metal box contacts the chassis.
I would be super to have an equivalent schematic (what's the typical drop in such a bridge? any special way to test them ?)

thanks

Eli Duttman 11th November 2006 04:45 PM

Bembel,

I think that the 2 parts are connected in parallel for 120 mA. current capability.

A 4 diode bridge is a 4 diode bridge. The forward drop in Selenium is greater than the forward drop in Silicon.

Don't bother testing them. Selenium rectifiers are ticking toxic time bombs. Replace those parts with 4X UF4007s and a dropping resistor.

bembel 11th November 2006 05:07 PM

Thx Eli, thanks for your answer but Ithink that the HV is floating each side of ground through an 85A2,
I found the problem, a dead nuvistor (on two) a the entrance :headbash: too bad because I have no spare ones !
Any way I wonder what formula use to calculate the dropping resistor for general Selenium bridge rectifier replacement.

bembel 20th December 2006 02:04 PM

I get a new 7587 nuvistor yesterday,
The diff amp can now be balanced, great.
But it seems that selenium rectifier has lost efficiency ! B+ is 355V after rect. in place of 420V, the electrolytics are OK or replaced yet.

Any tricks to compute the additional resistance when replacing with a Si bridge is welcome

Thanks.

kevinkr 20th December 2006 03:32 PM

Hi Bembel,
I suspect based on your pix that those selenium half bridges can be replaced with a single conventional silicon rectifier bridge of > 800piv 1A - 2A rating to be conservative. I would install the rectifier first with a 100 ohm 2W series resistor in one of the ac legs and then measure how far off you are and increase or decrease the value until you are close.

Those rectifiers are toxic and should be regarded as hazardous waste and if your community has recycling provisions for scrapped electronics I would take them there.

Note that the old nuvistors might not be bad if the filament voltage is low due to a bad rectifier. (assuming dc heating)

Edits for clarity and to correct an error

mississippi 20th December 2006 03:38 PM

2 Attachment(s)
This is what is inside the selenium rectifier.
2 peaces wil give a complete bridge.

ulibub 20th December 2006 04:03 PM

Re: Can anyone help, identifing selenium bridge hookup please.
 
Quote:

Originally posted by bembel
Here is a pict of the bridge rectifier, each block has 3 legs external metal box contacts the chassis.
I would be super to have an equivalent schematic (what's the typical drop in such a bridge? any special way to test them ?)


Salut bembel!

I think that each one of the two rectangular boxes consists of 2 diodes connected in series - the + describing the cathode of one diode, the - the anode of the other. AC lead is the center tap between these 2 diodes.

If now two of these boxes are connected as shown, the two cathodes (+) and the two anodes (-) give the DC poles and the two AC leads the AC poles of an ordinary 4-diode bridge.

Must say this is quite an unusual assembly, since I know these forms of rectifiers as full bridges (the ordinary tube radio set bridge), but 500 V also is quite high for such devices - usual values were 250 V / 100 mA. The metal box is electrically isolated from the diodes and gives contact to a heatsink.

And - quite probably - it isn't selenium which has been used in these boxes as a semiconductor, but Cu2O - "copper oxydul" (at least it is called like this in Germany) - but equally as toxic as selenium.... Voltage drop is a bit less than in tube rectifiers, but still far much than in si-diodes.

Salut de Sarrebruck
Uli

kevinkr 20th December 2006 04:08 PM

IIRC Copper oxide was used mainly in low voltage rectifiers, given the brand and vintage I still think it likely that those are selenium.. Either way both are toxic and should be handled with care. (Don't disassemble them!) If they burn up the smoke from them is extremely toxic so I would replace as soon as possible.

edit: fix typo

AndreasS 20th December 2006 07:54 PM

Hi Bembel,

this rectifier is for voltage doublers, not for bridges.

best regards Andreas

bembel 20th December 2006 08:06 PM

Thx all, I've just came back home.

all I can tell for now, is that the sel. or Cu. assembly is a full wave bridge on the schematic.

I'll scan it tonight , just wait an hour or so....

Thanks again for your answers I'm really puzzled about that, and I'm really grateful with your outputs. (it serves me)

As bthe beast is a VTVM all inputs regarding stability are most welcome.

just wait a few mins. for the schematic.

thx again


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