>Subject: Re: [AMPS] good, bad, ugly
>Sent: 3/27/1997 5:54 PM
>Received: 3/28/1997 2:37 AM
>From: Harv Shore, af006@lafn.org
>To: Rich Measures, measures@vc.net
>
>The quality of parts in the amplifiers and the de-rating thereof is
>not acceptable
>my 87A blew a tantalum capacitor rated at 15 v in a 15 volt circuit.
>the book talks about "flashover" in the tubes as being normal ..........
>From my experiences, flashovers are caused by something conducting inside
the tube envelope. Gas is one possibility. Gold melt-balls is another.
Gas enters the tube through a bad ceramic-metal silver-solder joint .
However, this is uncommon. Gold melt-balls are not.
Gold melt-balls are apparently produced by an oscillation condition.
The loose gold originates from the grid's gold plating. During
intermittent VHF/UHF parasitic oscillations, thin surface layers of gold
boil away and condense into tiny melt-balls. The semi-fix is to reduce
the VHF voltage amplification of the 3CX800A7s by lowering the
parallel-equivalent R of the VHF parasitic-suppressor assembly. Wherever
practical, it is helpful to reduce the VHF Rp of conductors between the
anode and the tune capacitor.
Just because a tube has some loose gold does not necessarily mean that it
is kaput. Interested persons are invited to phone or e-mail me for
details.
R. L. Measures,ag6k,805-386-3734
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