"EricM" wrote in message
...
On Apr 16, 4:01 am, "Arfa Daily" wrote:
"David" wrote in message
t...
"EricM" wrote in message
...
On Apr 14, 9:27 am, "David" wrote:
I also forgot to mention that the unit in question was
originally 6 -
1 inch square pieces in the stack, but only two
connections. The
other unit that I replaced with the 10A 600V units was
four pieces
about 1 1/8" (or just slightly larger) square, but had
three
connections. This particular unit was on the 15V side of
the supply
(filament supply for several 12 volt filament tubes) and
the 600V 10A
silicons seem to work fine. The other part of the supply
circuit -
the 600V plate supply - is where I used one of the 600V
10A jobs to
replace the 6-stack 1" square two-lead unit. Smaller but
more in the
stack must have equaled more PIV handling than the 600V
10A silicon I
put where it was (with no dropping resistor). Don't know
why it's so
hard to find info on these older rectifier units. They
hadn't gone
bad either, I'm just replacing them to prevent filling the
cutting
room with toxic stink if they should decide to fail...
I admit I am very confused at this point. The three leaded
rectifier was actually twoseleniumdiodes with a common
cathode or anode. Your replacement here should work fine but
check the filament voltage since it will be higher than
before by one or two volts. 12.6 volt tubes will not like 14
volts over a long time period.
There is no way a single 6 plate (stack)seleniumrectifier
can be a half wave rectifier for a 600 volt supply. Each
rectifier plate can withstand only about 50 reverse volts
and as others have said, you need at least three times that
for a PIV rating.
David
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
Thanks.
I looked at the schematic and as I suspected, none of theselenium
rectifiers are not involved in the 600 volt supply. CR2 A&B generate
the
12.6 volt filament voltage and can be adjusted with R1. No problem
there.
The otherseleniumrectifier CR1 is to generate a negative bias
supply.which is also adjustable and further clamped by Zener CR3. The
high
voltage is rectified by CR4 and CR5 which, I assume are silicon diodes
that you have not touched. The diodes you used for theselenium
replacement are an overkill but should not be related to your problem.
Are
you sure the -38 is really there and is in fact a minus voltage? If so,
at
this point I would check the CR4 and CR5 diodes and other parts of the
600
volt circuitry to see if you blew something else when working on this
unit.
David
I wonder where exactly the 600v next goes ? I see that there is a further
1:1 transformer-isolated supply to the "regulator filament". As they've
gone
to this much trouble to isolate it, could it be a regulator for the 600v
maybe ??
Arfa
Here's a link to the rest of the device; the vacuum tube amplifier
http://www.mediafire.com/?zdmyygvyfxn It's a large image in order to
be able to scale it so you can see what's what so I needed to do
a .pdf.
Assuming that the power supply runs without blowing the fuse, when it is
disconnected from the power amp, then looking at the schematic, it seems to
me that tracking down the problem will be relatively simple. But before
going any further down that route, can we get a bit clearer on how exactly
you have gotten to the point that you are at now? First, did the psu / amp
combination ever work before you started work on it, or has it been blowing
fuses all along ? The LT selenium reccies that you replaced just for
reliability's sake can be discounted I think. What was the reasoning behind
replacing the HT rectifier packs ? As you imply that these are differently
wired from the originals, could this be anything to do with the current
problems ? I'm sure that you have described some of this reasoning elsewhere
in the thread in odd bits, but it would be helpful if you could just go
through the whole of how you have reached the point you are now at, all in
one go.
Arfa