[Amps] Alpha 76 Plate Meter Calibration

[STEVEN & NANCY FRAASCH]

Bob:

Yeah, leave the line cord unlugged.

Measure the cathode resistor cold.  It should be a few ohms.  Plate current times that resistance is a voltage drop.  Assuming it is 3 ohms, 500 ma of plate current wll be 1.5V.  Try connecting a 1.5V battery prior (and check it with a DMM while adjusting) to the pot and then adjust the meter for 500 ma.  You're done.

73, Steve K0SF

----- Original Message -----
From: w5pvr at triton.net
To: amps at contesting.com
Sent: Monday, July 16, 2007 11:23:28 AM (GMT-0600) America/Chicago
Subject: [Amps] Alpha 76 Plate Meter Calibration

The Plate Meter on this restored two tube Alpha 76 needs recalibration. The
circuit uses the cathode voltage drop across a resistor measured by the
Plate Meter. The meter is converted to a volt meter by a series variable
resistor (pot.). it has a d'Arsonval 0-1ma basic movement If I knew the
resistance of the meter I could set it using Ohm's Law. Should be between 50
and 100 ohm's. I could do this hot but I shake real bad and I don't want to
get toasted. Any help out there?.
Bob

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