SB-200 users: a question.

[RAY FRIESS]

One cannot run 811A tubes as direct replacements for 572B tubes.   They will self destruct because the voltages and currents are higher for the 572B tubes.   You can run 572B tubes as direct replacements for 811A tubes, but not vice versa.


 
> Date: Mon, 19 Apr 2010 08:58:34 -0400
> From: infomet at EMBARQMAIL.COM
> Subject: Re: SB-200 users: a question.
> To: HEATH at LISTS.TEMPE.GOV
> 
> Won't 811As run in that thing? They are nearly indestructable and you'll 
> never notice a little powr loss. When I was a kid, I ran them at 1500-1600V, 
> zero bias, in a modulator for several years. You'll need some bias, I 
> expect, but that's not hard.
> 
> If you run a lot of CW, it would be good to add a grid leak, maybe that you 
> can switch in/out, and drive them into class C. Your output would be 
> increased somewhat over the linear case.
> Wilson
> W4BOH
> ----- Original Message ----- 
> From: "Kenneth G. Gordon" <kgordon2006 at VERIZON.NET>
> To: <HEATH at LISTS.TEMPE.GOV>
> Sent: Monday, April 19, 2010 12:11 AM
> Subject: SB-200 users: a question.
> 
> 
> > Well...since I have had both my SB-200s, I have been
> > having considerable difficulty obtaining 572Bs that are
> > reliable and will output what they are supposed to for more
> > than about a month.
> >
> > I run them as I am supposed to, keeping the grid current
> > well below 100 mA, but they seldom last. I don't abuse
> > them, and run mostly CW. I never allow them to show
> > color.
> >
> > I am very seriously considering replacing my 572Bs with
> > 813s, or some other heavy-plate tube of about the same
> > physical height.
> >
> > What do others use? How long do they last in normal
> > service?
> >
> > I am NOT pleased... :-(
> >
> > Ken Gordon W7EKB
> >
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