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@arrl.net>
To: "Tom Rauch" <w8ji@contesting.com>
Cc: <amps@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@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
>>
>>
>>
>>
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|