"Michael A. Terrell" wrote in message
m...

EricM wrote:

I have replaced two old Federal/ITT selenium rectifiers in an
amplifier power supply with new silicon diodes; the original part
numbers are 103H4AX1 and 104B1AX1. I can't find any reference to
either part on the web - anywhere - ITT can't even provide
information. Since one of the legs of the circuit supplies the plate
voltage (600V) I used 600V 10A diodes (NTE5815HC) to be safe. Problem
is, there is a time-delay relay that closes to engage the 600V
circuit, and without it attached to the amp; all tube supplies,
biasing voltage, etc. are normal. If hooked up, once the relay closes
- the main power fuse blows. I'm guessing I need a dropping resistor,
but it would be nice to have the original data on the selenium parts
to be able to figure out the value. The 600V and the -38V biasing
voltage are derived from the same part of the power transformer. The
-38 side works, but the 600V side reads upwards of 927 volts without a
load. Using a Variac, the plate voltages were above 600V at about 70
percent. Is there a way to find the original specs on these selenium
parts? Any leads would be greatly appreciated!


If the DC voltage is 600 volts you need higher voltage diodes. That
is a PIV rating, not an RMS rating like they used on Selenium
Rectifiers. As a minimum you need 600 * 1+1.414 PIV. That is 600 for
the voltage across the capacitor, and 600*1.414 (848.4) volts when the
AC line reverses polarity, for a total of 1448.4 volts. That assumes
your line voltage never exceeds the rated transformer input, no spikes
from motors or other heavy loads, no lightning induced surges. As a
MINIMUM, I would use three 1000 PIV diodes in series to replace each
section of the original rectifier.



So would I, along with 10 watt wirewound resistors with a starting value of
say 1k

Arfa