[Amps] Flashover and QSK board in TT Centurion

Tom Rauch w8ji at contesting.com
Mon Oct 1 12:39:54 EDT 2007

Woops, had the two mixed up.

With the quality of 3-500's today be sure to add a 20 ohm 
surge suppression resistor in the anode!!!!

73, Tom W8JI
----- Original Message ----- 
From: "Ignacy Misztal" <no9e at arrl.net>
To: "Tom Rauch" <w8ji at contesting.com>
Cc: <amps at contesting.com>
Sent: Monday, October 01, 2007 12:00 PM
Subject: Re: [Amps] Flashover and QSK board in TT Centurion

> Tom.
> TT Centurion has two 3-500Z. The red LED in that amp is 
> for power > 1250W.
> The flashover was a few minutes after turned on when idle.
> Ignacy
> On 10/1/07, Tom Rauch <w8ji at contesting.com> wrote:
>> Ignacio,
>> One problem with the TT amp is they have no positive
>> protection for excessive grid current.
>> A set of 3CX800's can be ruined in just seconds of 
>> operation
>> with excessive grid dissipation. Worse yet, the damage 
>> can
>> slowly accumulate over years of minor or very short
>> overloads. The overload LED warning light is really too
>> little much too late.
>> The failure mechanism is the gold from the grids migrates 
>> to
>> other areas of the tube. This happens from the kenitic
>> energy of the electrons hitting the grid, it is an
>> evaporation process without the necessity of the entire 
>> grid
>> overheating.
>> At this moment I have three TT amps here all with bad
>> 3CX800's, and the failure in all three is the tubes arc. 
>> The
>> tubes only HV test to 2-3kV average and have very low
>> emission, and that is a clear sign of severe gold 
>> migration.
>> If it was my amp, I'd put some type of very fast 
>> electronic
>> overload cutout in it. That would be number one mod.
>> 73 Tom

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