>All
>
>I have an Amp Supply LK 500 (2 3-500Z) that is starting to give me some
>grief.
>
>When I turn it on the Grid current goes negative and stays there.
A grid/fil shorted tube will do this. Lower VHF-Q parasitic suppressors
will make the amp more stable -- but with the tradeoff of c. a 2% power
out reduction at 29MHz.
>The plate current goes to about 200mA and also stays there. The plate
voltage
>looks OK. It is an intermittent problem that sometimes goes away if I
>power cycle the amp.
>
The filament double-helix expands when the tube is hot. This can cause
it to touch the grid cage when hot -- but not touch the grid cage when
cold. [photo of this phenomenon on p.15, Sept., 1990 *QST*.]
>I could use some help on debugging this.
>
>Thanks in advance
>
>Mike Walker VA3MW
>DX Cluster http://portcredit.net
>
>
>
>
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>
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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