[GreenKeys] 1N4007s

[Ralph Mowery]

----- Original Message ----- 
From: <WA5CAB at cs.com>
To: <drhouse at dls.net>; <WB6BLV at inreach.com>
Cc: <GreenKeys at mailman.qth.net>
Sent: Thursday, January 24, 2008 11:44 AM
Subject: Re: [GreenKeys] 1N4007s


>I certainly agree that the selenium rectifier should be replaced before 
>doing
> anything else.  Selenium rectifiers turned out to have a shelf life of 
> only
> 30-50 years typical.  But unless the one in this supply is a single diode 
> (only
> two terminals on it), I wouldn't use the axial lead 1N4007 unless I really
> had to pinch pennies.  A much neater conversion is to use one of the 
> square
> plastic bridge rectifiers.  Single hole mounting (under the original stack 
> maybe)
> and hard terminals that take either solder or 1/4" spade disconnects.  If 
> the
> original stack is only a full-wave rectifier (three terminals) you'll only 
> use
> three of the four terminals on the block.  But the things are cheap.  I
> bought some surplus 35 amp rated units yesterday for only $3.50 each.  For 
> this
> application, I would use one rated at least 400 PIV and 1 ampere.  I think 
> the
> most common ones in surplus are probably going to be rated 1000 PIV and 
> various
> currents.



----- Original Message ----- 
From: <WA5CAB at cs.com>
To: <drhouse at dls.net>; <WB6BLV at inreach.com>
Cc: <GreenKeys at mailman.qth.net>
Sent: Thursday, January 24, 2008 11:44 AM
Subject: Re: [GreenKeys] 1N4007s


>I certainly agree that the selenium rectifier should be replaced before 
>doing
> anything else.  Selenium rectifiers turned out to have a shelf life of 
> only
> 30-50 years typical.  But unless the one in this supply is a single diode 
> (only
> two terminals on it), I wouldn't use the axial lead 1N4007 unless I really
> had to pinch pennies.  A much neater conversion is to use one of the 
> square
> plastic bridge rectifiers.  Single hole mounting (under the original stack 
> maybe)
> and hard terminals that take either solder or 1/4" spade disconnects.  If 
> the
> original stack is only a full-wave rectifier (three terminals) you'll only 
> use
> three of the four terminals on the block.  But the things are cheap.  I
> bought some surplus 35 amp rated units yesterday for only $3.50 each.  For 
> this
> application, I would use one rated at least 400 PIV and 1 ampere.  I think 
> the
> most common ones in surplus are probably going to be rated 1000 PIV and 
> various
> currents.
>


The selenium stacks sure do smell when they burn out.  Everyone should smell 
a at least one..A smell you never forget.  Sort of like smelling a skunk.

One other thing to keep  in mind is the output voltage will be much higher 
when the silicon rectifiers are subistuted.  I am thinking a selenium stack 
drops around 2 volts or so per plate.  It may be more or less as I did not 
take the time to look up the exect value.  The silicon rectifier will only 
drop about 1 volt total.  You need to add a series resistor to compensate 
for this in most circuit.   I would guess that around a 15 to 30 ohm 
resistor with a rating of 15 watts or greater would be needed in the 
Teletype power supply.

A quick glance at one circuit seems to indicate a full wave bridge.  As 
mentioned those things can be picked up very reasonable.  Get one with a 400 
volt or greater rating and a current rating of 2 amps or beter and you 
should be covered for most anything..  Four of the individual rectifiers can 
be used, but more trouble.