[Amps] Flashover and QSK board in TT Centurion

[rgroh at swbell.net]

I am certainly not an expert on HV and high power amps but I certainly could guess that you had an low impedance (e.g. an arc someplace - maybe in the tube? or across air between components or across a dirty surface between a high voltage connection and ground or ????) develop downstream of the rectifiers and that the current surge blew up (literally) the traces. 

The current spike in the traces also caused an induced voltage spike in the traces in the QSK board traces and components which then blew up the CMOS gates et al. 

A 2nd possibility is that there was a common ground path such that the current spike caused a jump in the apparent voltages on the CMOS logic such that CMOS again were driven beyond their limits and blew up.

It is amazing the degree of damage that big current spikes can do. The fact that the traces on the HV board vaporized is testimony to the very high current that must have flowed.

So I would suggest the following:
1.    You will get a number of excellent suggestions from others on this list
2.    Look carefully for any possible areas for an arc to develop or where one might have developed(such as burn marks, pinholes in insulated wire), etc
3.    Look at the QSK board - maybe it should be mounted someplace else farther away from the HV board.
4.    Look into a 'glich protector' on your final tube if it doesn't already have one.

Best of luck. 

73
Bob, WA2CKY


----- Original Message ----
From: Ignacy Misztal <no9e at arrl.net>
To: amps at contesting.com
Sent: Monday, October 1, 2007 8:06:53 AM
Subject: [Amps] Flashover and QSK board in TT Centurion

A few minutes after being turned on, my TT Centurion made a loud bang
and went dead. The trace on the HV board from the transformer to
diodes evaporated. There was not any damage visible anywhere else.

I patched and the amp amplifies but it is always on, and additionally,
the red LED in the power meter is always on. After checking, all CMOS
(4011 and 4093) inputs and output are 14V.

This is the third problem with the QSK board. It seemed to occur to
the previous owner and it occured to me before after replacing a fan,
although there was not any flashover or band and just one gate wrong.

I ordered the ICs + sockets to avoid (un)soldering. But there are two questions.

1. Why that trace burned? There should not be high currents between
the transformer and the rectifiers. If there was any probelm with the
rectifiers/capacitors, perhaps something else would have fried as
well.

2. Are CMOS chips too fragile to be put 1 inch directly above the PS board?

73,
Ignacy
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