Amps
[Top] [All Lists]

[AMPS] Grid Current problem

To: <amps@contesting.com>
Subject: [AMPS] Grid Current problem
From: wc7m@vcn.com (W7CW Jay E Ostrem)
Date: Sun, 06 Dec 1998 10:35:35 +0000
I finally got my YC-156 on line, sort of.  As noted in my earlier
transformer post, I am using about 3400Vdc B+, which effects my design RL
of 2400 ohms which the amp was designed for.

The following problem doesnt even require application of B+, and is
something I haven't seen before.

The amp design looks like any run of the mill 3-500Z cicuit, but is
physically 3X bigger.

When the filaments come up, the grid current meter pegs below zero.

When I short the bias cut off resistor the grid current goes way positive.

This is without excitation, or B+.

I am using a variable shunt regulator (two terminal device) in place of a
bias zener, and this is located directly below the filament transformer on
the other side of the chassis.
I can vary the bias from .6 to 30V, the grid current goes from 25mA to "oh
my god"
 
I have checked the filament circuit bypass caps (.01 disc ceramics) with an
ohm meter, and nother is shorted.

Nothing is shorted in the tube (all open).

I tore the covers off and checked my wiring of the metering circuits, all
appears OK.

The grid current indication is the same with the B+ attached or detached;
as is with the dummy load and input circuit.

What gives?

73 Jay W7CW
                              73 Jay W7CW

                                 1AB Ranch
                                 Gillette, Wyoming

--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm


<Prev in Thread] Current Thread [Next in Thread>