[Amps] NOS 811's & 30L1

[Eddy Swynar]

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
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps