Hi Guys,

I am just about to start on a 2kV supply for a 4CX250 amp. I have a
750VA 1500V transformer and a couple of 15uF 7.5kV caps.

In the full wave rectifier department I seem to have a few options:

1) A bridge of Microwave oven rectifiers like the NTE517, 15kV PIV,
550mA avg, 200A peak surge

This is by far the simplest and has the same surge capability and
500ma / 1500V is in the same ball park as the 750VA transformer
rating.

I assume that a small capacitor across each of the 4 devices would be
wise -- any suggestions of value.

2) A string of 3 or 4 1N4508 rectifiers, 3-4kV PIV, 3A avg, 200A peak
surge

The standard topology for this seems to be voltage equalizing
resistors across each rectifier along with a transient absorbing cap -
maybe 10nF.

I am sure I have seen some comments that the resistors may reduce
reliability (short of using MELF, most metal film resistors seem to be
rated at 300-500v). Are their other easily available higher voltage
parts ?

Finally a 1500V sine wave has a peak of 2100V, so 3 x 1kV rectifiers
is never going to approach the total avalanche voltage, so why bother
with the balancing resistors? Sure, the caps have a more balanced
voltage across them if the resistors are included...

This design involves 12 x (rectifier + resistor + cap) which is
starting to take up some PCB space where some well insulated posts
are all that is required to support 4 microwave oven rectifiers.

All comments appreciated,

Thanks,

Mark

MarkAren wrote:
Hi Guys,

I am just about to start on a 2kV supply for a 4CX250 amp. I have a
750VA 1500V transformer and a couple of 15uF 7.5kV caps.

In the full wave rectifier department I seem to have a few options:

1) A bridge of Microwave oven rectifiers like the NTE517, 15kV PIV,
550mA avg, 200A peak surge

This is by far the simplest and has the same surge capability and
500ma / 1500V is in the same ball park as the 750VA transformer
rating.

I assume that a small capacitor across each of the 4 devices would be
wise -- any suggestions of value.

2) A string of 3 or 4 1N4508 rectifiers, 3-4kV PIV, 3A avg, 200A peak
surge

The standard topology for this seems to be voltage equalizing
resistors across each rectifier along with a transient absorbing cap -
maybe 10nF.

I am sure I have seen some comments that the resistors may reduce
reliability (short of using MELF, most metal film resistors seem to be
rated at 300-500v). Are their other easily available higher voltage
parts ?

Finally a 1500V sine wave has a peak of 2100V, so 3 x 1kV rectifiers
is never going to approach the total avalanche voltage, so why bother
with the balancing resistors? Sure, the caps have a more balanced
voltage across them if the resistors are included...

This design involves 12 x (rectifier + resistor + cap) which is
starting to take up some PCB space where some well insulated posts
are all that is required to support 4 microwave oven rectifiers.

All comments appreciated,

Thanks,

Mark

Mark, The 1N4007 or JE125, NTE125 diodes are 10 cents each in groups
of 100. Get a bunch of one or the other, see what you can get at 2kv
FWB rectifier, less than 1 amp. Power up surge may be a problem. No
equalizing R or C. Should be cheep enough to run several in each leg
of the FWB to see what you can get. I seem to remember that the
equalizing R and C has been decided not needed.

Gary N4AST