On 4/16/08 9:59 AM, in article
, "EricM"
wrote:

On Apr 16, 7:25 am, Heinz Schmitz wrote:
EricM wrote:
Here's a link to the schematic; after replacing CR1 and CR2A/B with
10 amp 600 V silicon diodes, when the relay closes to enable the 600V
plate voltage, the main power fuse F1 blows. I'm not sure I need
dropping resistors, because the output voltage on the 12.6 and -38
terminals is very close to what it should be. Is there something I'm
missing? http://img410.imageshack.us/img410/4691/1567pscb9.jpg

I'd disconnect the relay (S-1 and VS3) and comfortably check all other
voltages (value, polarity, ripple). If ok, I'd power off and check the
electrolytics in the 600 V circuitry (otoh, if they do not look
exploded, they are probably ok). Then the fault is somewhere else in
the device.

BTW, what is connectors 2 on CR4 and CR5?
Does somebody switch from 8 to 2 at some point?

Regards,
H.

This is also a problem. The original 1N1239 rectifiers only have
three pins on the bottom at locations 4, 6, and 8, and the 'key'.
There is no pin on the device at #2, but the two wires from the relay
switch pole that is NC (until the coil is powered) are tied to #2 the
socket. (It's not connected to chassis ground either, which might be
inferred by the schematic - they're just meaning that two wires are
tied to #2 on the socket, even though there is no pin on the 1N1239 at
that location.) I ordered newer replacements for these from
americanmicrosemiconductor.com - they were the only place on the
internet that had exact replacements for the '1N1239' Sarkes Tarzian
center tapped rectifier. HOWEVER, when the new replacements - that
look much more like a metal envelope vacuum tube than the originals -
they have all pins and are shorter, there's no 600V on the output.
Just a few millivolts of nothing. The newer units must be wired
differently than the originals. The 1N1239 was a replacement for the
5R4 vacuum tube rectifier; I also located another online vendor that
sells 'C-Cap' rectifier replacements and he states that his 5R4
replacement should work. I'm debating whether or not to order some to
test though, since the originals seem to be oddballs of some type.
And essentially what the relay does, is shunt resistor R5, as pins 2
and 8 seem to be looped no matter what position the relay is in. This
one is really a pain - I've never encountered a PS like this one...

All the "relay" does is to complete a low resistance path from the 600 V
voltage source, to the filter caps AFTER a time delay has (gently via 15k)
pre-charged the filter caps.

Disconnect the 600V lead from the PS to the Amp and see which way the
problem is. If the fuse still blows, trouble shoot the PS. You do have a
voltmeter?