Has anyone ever used non-contact current measurements for plate and grid
current.
If you had sufficient shielding you could run the plate and cathode DC leads
thru next to
the IC so that the plate and cathode currents cancel leaving grid current as a
result.
Probably have to use a copper shield around the IC so that no RF screws it up.
I have seen noncontact passive meters where you pass a conductor thru it but
they are used mostly in cheap auto battery and charging systems.
73
Bill wa4lav
________________________________________
From: Amps [amps-bounces@contesting.com] on behalf of Jim Thomson
[jim.thom@telus.net]
Sent: Wednesday, November 30, 2016 9:33 AM
To: amps@contesting.com
Subject: [Amps] Single Band Amplifiers One Power Supply
Date: Sat, 22 Oct 2016 19:07:58 +0000
From: Bill Turner <dezrat@outlook.com>
To: Amps group <amps@contesting.com>
Subject: Re: [Amps] Single Band Amplifiers One Power Supply
On Wed, 19 Oct 2016 18:47:05 -0500, W7RY wrote:
>How would you go about metering them?
REPLY:
In modern amps. both the B- and B+ are NOT connected to ground, but
left floating. The grid current meter is connected from B- to ground.
The plate current (actually cathode current) meter is connected in the
B- lead BEFORE the grid current meter , i.e. on the power supply
side of the B- lead, not the cathode side.
Sounds weird, but it works. Check the schematic of any late model
grounded grid amplifier and that's how they do it.
If you want to use a single switched meter for all the amps. simply
put a low value resistor on the order of one ohm or so where you would
normally put the meter and them simply measure the voltage drop across
it. That way you can switch the meter from one amp to another without
disturbing current flow. Simple Ohm's law will give you the values.
73, Bill W6WRT
## The plate meter will only read plate current, and not cathode current. The
grid meter
will only read grid current. This assumes u wire the meters like have been
shown in every arrl
book for years.. for a GG triode. POS of both plate and grid meter bonded
together...then off to the
CT of the fil xfmr. Neg off plate meter to B-. Neg of grid meter to
chassis.
Jim VE7RF
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