[Amps] Running 3-500s upside down

[R.Measures]

On Mar 16, 2005, at 5:14 AM, Pete Smith wrote:

> I understand that running 3-500s on their side risks internal shorts.

I ran a fil-on 24/7 test with a horizontal 3-500Z to determine filament 
sag.  The sag rate was quite slow -- which was determined by grid-fil 
BDV.   It appeared that rotating the tube 180º every 1000-hours or so 
would have prevented any fil-grid clearance problem.
> I
> need to do some trouble-shooting on my modified SB-220's relay/bias
> switching circuit, however, which would be much facilitated if I could 
> key
> but not drive the amp (no RF out) with it upside down.  I can pull the
> tubes if I need to, of course, but would prefer not to.

Operating 3-500Zs base up or base down is okay.  In a SB-220, most of 
the hot exhaust come out the left side of the cabinet, so upside down 
should be no problem.
>
> 73, Pete N4ZR
> The World HF Contest Station Database
> was updated 12 January 2005
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>
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org