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Hung Chang 5604 voltage multiplier

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HMartins:
Hi.

I have a Hung Chang 5604 oscilloscope whose CRT (150CTB31) voltage multiplier is faulty. Works nicely until some hours after when scope display 'zooms in'.

All voltages around high voltage transformer drop to around 1/3 of the normal. Overload security diodes of the transformer power transistor start to drain current from transistor base. This avoids full disaster.

After isolating the multiplier input all voltages come back to normal.

In the (quite simplified) manual there is no reference to the multiplier. Could it be a doubler, tripler...? In normal circumstances the multiplier input is 2400Vpp, sort of sinusoidal.

For the moment I will close the unit and install a small fan on top to keep it cooler.

In https://www.eevblog.com/forum/testgear/beckman-industrial-9102-scope-problem/msg1587742/#msg1587742

... it says this CRT (150CTB31) it is a 10KV unit. Could someone help me figuring out whet type of multiplier it mast use (doubler, tripler, quadrupler?...) providing the transformer supplies 2400Vpp?

Any help is highly appreciated.

Regards
Henrique Martins

jonpaul:
usually a tripler.  Very common part.

Otherwise failures in CRT HV are,high-voltage resistors, and,the HV transformers

Jonpaul@ix.netcom.com

HMartins:
Thak you for the answer.
H. Martins

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