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Re: [Amps] NOS 811's & 30L1

To: "Mike Lord" <>
Subject: Re: [Amps] NOS 811's & 30L1
From: Eddy Swynar <>
Date: Wed, 21 Sep 2011 15:49:59 -0400
List-post: <">>
Hi Mike,

I wonder just exactly how those 811As were "matched" at source...?

Years ago when I built my first HB kilowatt amplifier---using 4 surplus 
811As---I learned the hard way of the importance of proper matching...and I had 
the 811As with holes on their plates the size of your baby fingernail to prove 
it, too! Hi Hi.

I finally settled on "matching" these tubes by resting current, one tube at a 
time. Any wide divergence from "the norm": in this way, & that tube was not 
considered to be suitable. It worked for me, but I sure went through a TON of 
811As before I finally learned (lucky for me they were only a buck, or two, 
apiece from North American Electronics in Montreal).

~73~ de Eddy VE3CUI - VE3XZ


On 2011-09-21, at 3:25 PM, Mike Lord wrote:

> I just completed the restoration of a 30L1, i.e., new Harbach board, "matched 
> set" of 811's.  Brought the unit up slowly with a Variac.  110 VAC line 
> voltage, 1800 VDC unloaded on plates.  All seemed ok.  Hooked up the unit to 
> the rig.  Turned the 30L1 on and blew up the glitch resistors.  Smoked up the 
> place.  Checked the unit for damage beyond the glitch all checked ok.  
> Brought the unit up slowly with the Variac and at about 400 VDC one tube 
> began showing purple glow and slight arcing.  Changed out the tube and all 
> was well.  Here's my question.  The 811 vendor tells me the problem is the 
> 1800 VDC on the plates.  "Too much for an 811"  I realize the caps on the 
> Harbach are large thus more B+, but there have been many of those boards 
> sold.  The 30L1 book says 1600 VDC unloaded.  The 811 is rated at 1500 V.  So 
> what are all the 30L1 owners doing besides changing over to a 572B?
> Thanks.  Mike K4ELV
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