Re: Tek 576 Curve Tracer HV Replacement Transformer

Tom Bowers


Why is a resistor in series with the multiplying ladder necessary?
I have un-potted the X14 multiplier from a 7904 and there is a 10 Meg Ohm
1/2 W Carbon resistor on the output high voltage lead, connected to the
last diode in the ladder.

The reason I had to un-pot one was to design a replacement, as I had blown
it up by discharging it. If there is even the slighted difference in the
value of the capacitors, a sudden discharge applies unequal voltages to the
diodes and at some point a diode gets destroyed. When doing this, the full
21KV is applied across the 10 Meg resistor.

Carbon is important because it is more forgiving to such a voltage
overload. A metal film resistor is not as forgiving. A 1/2 W resistor has a
higher voltage overload capability than a 1/4 W resistor. In the
replacement that I am building, I intend to put three 3.3 Meg 1/2 W carbon
resistors in series on the output lead.

To anyone who knows where X Ray images might be located, I would certainly
appreciate a clue so I could look at them. Also, I can share pictures of
the one I un-potted. Not pretty, but maybe somewhat useful.

Tom Bowers

On Tue, Apr 7, 2020 at 8:34 PM Ernesto <ebordon@...> wrote:

Michael, Chuck,

Why is a resistor in series with the multiplying ladder necessary? Isn't
the internal helical coating of the CRT a load and a drainage means of the
ladder capacitors?
In the 547 there is a 1 Mohm 1/4 watt resistor after the ladder, followed
by a 500pF capacitor to ground.
In the 7704A there is no visible resistor, and the do-it-yourself circuit
does not show one inside the X14 module.


Join to automatically receive all group messages.