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amdx[_3_]

On 3/5/2014 5:42 PM, wrote:
"The suggested mod uses high current
FETs (12 or 15 amp). Just doesn't seem correct.
Looking at the schematic it shows 165 ohms in series with each plate,
with a B+ of 53V, the current would be limited to 320ma. "

Correct. Actually there is nothing really "in series" with the plates.

Are you sure?

I have HP1725A schematics from two different sites and both have a 165
ohm resistors in series with each plate. Then I find another 50 ohms in
series with the transistor emitters (the ones in your defective IC)

They operate electrostatically, the only load they impose is capacitive.

The way they have it configured is apparently they have electrodes at
each end of the plates, for whatever reason.

One electrode goes to the transistor that pulls it low, the other
electrode goes to the 165ohm resistor that is tied to +53V.
Yes it is push/pull.

Post a schematic or something to convince me the schematic I have is
not correct.

btw, the 165 ohm resistors seem to reside on their own board (A5A1)
all by them selves.

Mikek

PS. I have seen some owners raving about their HP1725A scopes.