[Heathkit] SB-610 & SB-620 Selenium Diodes

[Kim Herron]

Hi again Carl,


>OK the 1N4007.   Put 2 in series.
>I'm not real-up on diodes that much you'll need to forgive me.
>According to the Mouser website the 1N4007 is rated at 1000 Volts.
>It says the "Peak Repetitive Reverse Voltage".... Is that the same as 
>"PIV" in the Heathkit manual ?

         Not exactly, but for ratings purposes, yes

>Info also IDs "Average Rectified Forward (Output) Current" as  1 Amp ?
>That means 1 amp when the Heathkit manual only calls for  2 ma ?
>Heathkit "under rated" the current i asume.

         No, the original selenium rectifier was rated at 2 
milliamps.  What you using these rectifiers for is the
HV that is applied to the CRT for acceleration voltage.  So current 
requirements are very low.  When these scopes were
originally designed (late 50's, early 60's) the solid state diodes were 
MUCH more expensive and weren't needed for the
purpose.  The alternative was to use a HV rectifier tube which was much 
more expensive.  What Heath put in the circuit
was fine for what it was used for.


>So  i  am looking to string two 1000 volt diodes together to get my 2000 
>volts ?
>Then within the string i add each 1 amp and that gives me 2 amps ?

         No, you have it backwards.  The current flow in the circuit is the 
same across all of the components.
The voltage drop across the diodes divides (equally in this case).  So each 
diode sees the same current load,
and half the voltage drop.  Basic Ohm's law here.  One more thing.  Current 
flow in the circuit is dependant on the
draw from the load the circuit, in this case the CRT.  The maximum current 
rating of the diode does not determine
what the current flow in the circuit is.  The only thing that we're 
interested in here is that the maximum rating of the
component that we're using for replacement is at or above the item that it 
is replacing.  In this instance it is the selenium
rectifiers.  The diode rating is well above the needed 2 milliamps so it is 
suitable


>So did seleniums just dissapear & more the less replaced by these ?

         Several factors made selenium rectifiers cease to be used in 
rectifiers applications.
Probably the biggest factors have to do with the diodes themselves.  The 
manufacturing processes
for solid states components have come way down in cost, reliability and the 
fact that there
are no EPA hazards that I'm aware of in disposal of manufacturing 
byproducts, like with selenium, which is
quite poisonous, or so I understand.

>Got two busted seleniums  ( one @ ) in the sb 610 & sb 620.
>Thank you very much for your kindness & wisdom.
>73s
>Carl k4zrd
>
>
>
>----- Original Message ----- From: "Kim Herron" <kherron at voyager.net>
>To: "Carl Lowry" <l_carlj at bellsouth.net>; <heathkit at mailman.qth.net>
>Sent: Monday, July 04, 2005 12:05 PM
>Subject: Re: [Heathkit] SB-610 & SB-620 Selenium Diodes
>
>
>>Hi Carl,
>>>Looking for a source for Selenium Diodes to be used in redoing the 
>>>SB-610 & SB-620 power supply sections.
>>>They are  identified as part number  57-44
>>>Manual says they are:  2 ma, at 1750 PIV.
>>>Any suggestions please ?
>>
>>         Yes, use the appropriate solid state diode equivalent.  You 
>> won't find selenium and you don't want them
>>even if you do.  If nothing else, use 2 1n4007 diodes in series.
>>
>>
>>Thanks!!
>>
>>Kim Herron  W8ZV
>>1-616-677-3706
>>Outgoing mail scanned for virus and worms
>>with McAfee Virus Scan
>
>
>
>
>
>_____________________________________________________
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Thanks!!

Kim Herron  W8ZV
1-616-677-3706
Outgoing mail scanned for virus and worms
with McAfee Virus Scan