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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