Steve Maki wrote:
>K8GM asked me to post this plea for help...
>
>He is playing around with a GS-35, and so far hasn't been able
>to be happy.
>
>The symptom is as follows:
>
>As the drive is increased, at some relatively random point,
>the tube makes a single pop - he says it sounds like someone
>snapping their fingers. He sees no abnormal meter indication
>or change in output - in fact, the amp continues to operate
>normally. There's only one small problem - when the pop happens,
>it distorts the plate choke windings. They sort of get all
>bunched up as if some large force tried to slide them along
>the form with enough force to stretch the wire and cause over-
>lapping.
That's a sure sign of a large current pulse through the choke,
generating magnetic forces which try to pull the turns together.
>No fuse blows,
That may say as much about the fuse as anything else :-)
>and except for this occasional pop,
>the amp works great.
>
>His supply is c. 3500V, and he's tried a couple of different
>chokes, both commercial and homebrew. It appears to be strictly
>a tube issue, rather than associated circuitry, but in our
>preliminary web search haven't come up with references to this
>problem.
>
It has been discussed here, more than once. There are internal photos of
an arced GS35b at www.ifwtech.co.uk/g3sek/misc/gs35a.jpg and
...gs35g.jpg
>What's happening here? Does the GS-35 need some kind of magic
>pre-conditioning?
Many do; some don't. Remember that the GS35b is one of the older
generation of Russian tubes "made in a tractor factory" so there is some
variation. Also it may have been in store for some years, so there may
have been some outgassing of internal structures.
>He has idled the tube at full voltage for a
>few hours, but that didn't do the trick.
>
Think about more like a 24-hour burn-in - see recommendations at
www.nd2x.net
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
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