[Amps] grid fuses

[R L Measures]

On Jul 21, 2006, at 7:13 PM, Tom W8JI wrote:

>
>> Not really,
>>
>> its quit common that tubes like YL1050, TH347 etc. which
>> are very high gain
>> metal ceramic tetrodes for linear mode of small
>> tv-transmitters and linear
>> service arc internally from time to time.
>> It does not matter whether they are new out of the box or
>> being in service
>> for a long time.
>> Those tubes are extremely expensive and nobody throws them
>> away.
>> Everybody uses the circuitry in the power supplies which
>> the manufactory
>> suggests and never a grid fuse or grid resistor but direct
>> ground
>> connection.
>> The YL1056 in my 2m amp is running now perfectly for
>> almost 20 years with
>> regular arcs even in standby, it does not matter at all,
>> the P/S quickly
>> resets and during a contest I do not loose any qso by
>> that.
>>
>> 73
>> Peter
>
> Thanks Peter,
>
> I was sure anyone with experience in manufacturing new PA's
> with power grid tubes would know this, but maybe some do
> not. I guess it is good to repeat it.
>
> If I tossed back 3CX3000A7's that arced when brand new,

An Eimac 3cx3000A7 that arced during final test would undoubtedly be  
tossed into the scrap bin.

> about 50% would go back. Those very same tubes, once
> "burped" a few times, give many many years of service. This
> is really common with many tube types in many classes of
> service.
>
> If it wasn't a problem, the factory would not put active
> getters in large power grid tubes!

Large ones have an ion pump.  I disassembled a kaput 4cx5000A and I  
did not see any gettering material.
>
> 73 Tom
>
>
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R L MEASURES, AG6K. 805-386-3734
r at somis.org