Alex, this is a familiar problem with nearly all grounded grid amplifiers.
Your problem is caused by current from the HV supply leaking to chassis
ground rather than returning directly to the B- input on your HV power
supply. The grid current meter reads backwards because the current is
flowing up from the chassis ground, through the resistor that goes between
cathode of the tubes and ground, and then back into the B- return. The grid
current meter measures the voltage drop across that resistor, and since the
current is flowing from ground up through the resistor, the meter reads
backwards.
One common cause of this phenomenon is a gassy tube. An internal
cathode-grid short can also cause the problem, though in that case the meter
would normalaly peg backwards with great force. Another possibility is a
shorted safety diode that most grounded grid amplifiers place between the
tube cathodes and ground. The anode of the diode is grounded and normally
has no impact on the circuit. If it shorts out, however, possibly because of
a flashover, it can cause the symptom you observe.
73,
Jim W8ZR
> From: Alex Barbon <dv1tbx@gmail.com>
> Subject: [Amps] Henry 2k Classic Grid meter problem
> To: Amps@contesting.com
> Message-ID:
> <CAMV3qPaAYjEc3GGzEM2ygObx+qzhMb3Y=yQxmXVWVbWZ6DPVcQ@m
> ail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Hi to all
>
> I want to ask if someone encounter this situation with the 2k classic.
When
> the amp is OFF the IG meter rest in zero point , but when i turn ON the
amp
> the IG meter moves to counter clockwise movement. Its not moving hard to a
> point it will break the needle, just a soft movement backwards and stay
just
> there, it will move to clock wise direction when i TX on the radio it will
> show the IG reading of the amp,but iam not sure if its the correct reading
> since it rest on the backward possition of the zero point.
>
> I tried to remove the parasitic suppressor on the tube and power it up,
the
> backward meter movement was gone, the meter rest on the zero point, a bit
> puzzle where that backward meter movement came from or causing it.
>
> Hope someone can give info how to trouble shoot it. The meter wiring and
> parts seem still in the original.
>
> 73,
> Alex
>
>
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