[Boatanchors] 813 grid to filament short

[manualman at juno.com]

My SB-200 has the same original horizontal 572B's in it that were
installed in 1969. Been in use all that time and from roughly 1995 to
present also on AM. Never had any tube elements sag or short. Personally,
I think the physical placement of the tubes is quite sound but then again
I'm not a satellite engineer either. I was a "suit" for the last 20 years
of my engineering adventure although I don't recall having any
catastrophic design failures either. A local ham, who had contesting
fever, had a homebrew amp (pair of 813's mounted horizontally) that he
used for roughly 50 years and never had an 813 failure.

Pete, wa2cwa

On Thu, 1 Oct 2015 20:11:58 -0400 rbethman <rbethman at comcast.net> writes:
> On 10/1/2015 7:33 PM, Paul Baldock wrote:
> > At 01:37 PM 10/1/2015, you wrote:
> >
> >> The entirety gets back to 813s and mounting them horizontally. 
> Bad 
> >> move!  W3BYM uses 4 813s to modulate 4 813s.  Should one dig up 
> the 
> >> old ER issue, you'll find that he mounted them vertically! The 
> only 
> >> _intelligent_ way to do so.
> >
> > Well I'm an intelligent person, I think. At least intelligent 
> enough 
> > to read the manufacturers data sheet that says " in a horizontal 
> > position, the base pins No2 and No6 should be positioned 
> vertically 
> > one above the other"
> >
> > Then of course there's those beautifully constructed 813 amps in 
> the 
> > 1968 ARRL handbook 
> > 
>
http://www.arrl.org/files/file/protected/Group/Members/Technology/tis/inf
o/pdf/68hb195.pdf 
> 
> > . Yes the tubes are on their side, and that seems like a quite an 
> 
> > intelligent article also.
> >
> > - Paul
> The manual that you read regarding the 813s simply states "IF" you 
> are 
> going to mount them horizontally, to mount it in that fashion.
> 
> Does this same manual say that the filament will NOT sag and short 
> out?
> 
> The manuals on 572Bs read essentially the same way.
> 
> The last I've seen, no manual states that the filament won't sag, 
> nor 
> that it won't short to the grid.
> 
> Engineers also designed the Chevy Vega.  It took Cosworth to make it 
> a 
> viable dependable vehicle.
> 
> I mentioned W3BYM and his home-brewed 813s modulating 813s.  It 
> would be 
> an additional comment to add that he was also a satellite engineer.  
> The 
> same for the late WC3K.
> 
> Neither of them has/had significant failures while working for 
> Comsat, 
> nor the projects they took on in their shacks.
> 
> I look at the entirety, and then I look at what stays up and 
> running, 
> versus what develops failures.
> 
> Personally, I do believe that this methodology is indeed 
> intelligent.
> 
> My 813 GG amp never had a single issue.  The tubes were mounted 
> vertically.  They also had a blower running over them, and their 
> sockets 
> were mounted below the chassis to allow air to flow upwards from 
> below.
> 
> Different strokes for different folks.  I have yet to have a final 
> PA of 
> mine ever blow.
> 
> Then again I never have tried using sweep tubes for finals.
> 
> Regards, Bob - N0DGN