Hello All! How do I measure grid bias voltage (am using Simpson analog volt/ohm meter) ex.let's say I have a 6J5 tube and let's say the grid voltage needs to be negative 8 volts ,so where do you place the probes ,on the grid (black)and cathode (red)???or can you only do this mathematically if you know the plate voltage and current etc??Thanks for info

Hi Chris

You need a high impedance meter to measure grid voltage. Not sure about your Simpson but VOM's will load down grid voltage.

To directly measure grid voltage connect the black wire to grid and red wire to cathode. Grid voltage is measured with reference to cathode of a tube.

In many circuits tubes will be biased with a cathode resistor. Meter loading won't have much of an effect if you measure across this resistor. This gives a direct reading of grid voltage provided there aren't bad components in a circuit. Red lead to cathode, black to B- or where the grid resistor returns.

Can't figure this voltage mathematically unless designing a circuit. Tube emission, leakage, resistor tolerance and capacitor leakage will effect the voltage.

Norm

:Hello All! How do I measure grid bias voltage (am using Simpson analog volt/ohm meter) ex.let's say I have a 6J5 tube and let's say the grid voltage needs to be negative 8 volts ,so where do you place the probes ,on the grid (black)and cathode (red)???or can you only do this mathematically if you know the plate voltage and current etc??Thanks for info
:

A lot of old time documentation assumed you were using an ancient V.O.M. with 1000 or 2000 ohms per volt.

When using a modern digital meter, the readings will look high. You can always shunt a 2000 ohm resistor between grid and cathode to simulate the behavior of old meters, and get some idea of what is going on, although this is not a perfect science.

As for the almost ancient Simpson's they are somewhat in the middle, about 20,000 ohms per volt for the best of them, so far as I know.

:Hi Chris
:
: You need a high impedance meter to measure grid voltage. Not sure about your Simpson but VOM's will load down grid voltage.
:
: To directly measure grid voltage connect the black wire to grid and red wire to cathode. Grid voltage is measured with reference to cathode of a tube.
:
: In many circuits tubes will be biased with a cathode resistor. Meter loading won't have much of an effect if you measure across this resistor. This gives a direct reading of grid voltage provided there aren't bad components in a circuit. Red lead to cathode, black to B- or where the grid resistor returns.
:
: Can't figure this voltage mathematically unless designing a circuit. Tube emission, leakage, resistor tolerance and capacitor leakage will effect the voltage.
:
:Norm
:
:
::Hello All! How do I measure grid bias voltage (am using Simpson analog volt/ohm meter) ex.let's say I have a 6J5 tube and let's say the grid voltage needs to be negative 8 volts ,so where do you place the probes ,on the grid (black)and cathode (red)???or can you only do this mathematically if you know the plate voltage and current etc??Thanks for info
::
:

:A lot of old time documentation assumed you were using an ancient V.O.M. with 1000 or 2000 ohms per volt.
:
:When using a modern digital meter, the readings will look high. You can always shunt a 2000 ohm resistor between grid and cathode to simulate the behavior of old meters, and get some idea of what is going on, although this is not a perfect science.
:
:As for the almost ancient Simpson's they are somewhat in the middle, about 20,000 ohms per volt for the best of them, so far as I know.
:
::Hi Chris
::
:: You need a high impedance meter to measure grid voltage. Not sure about your Simpson but VOM's will load down grid voltage.
::
:: To directly measure grid voltage connect the black wire to grid and red wire to cathode. Grid voltage is measured with reference to cathode of a tube.
::
:: In many circuits tubes will be biased with a cathode resistor. Meter loading won't have much of an effect if you measure across this resistor. This gives a direct reading of grid voltage provided there aren't bad components in a circuit. Red lead to cathode, black to B- or where the grid resistor returns.
::
:: Can't figure this voltage mathematically unless designing a circuit. Tube emission, leakage, resistor tolerance and capacitor leakage will effect the voltage.
::
::Norm
::
::
:::Hello All! How do I measure grid bias voltage (am using Simpson analog volt/ohm meter) ex.let's say I have a 6J5 tube and let's say the grid voltage needs to be negative 8 volts ,so where do you place the probes ,on the grid (black)and cathode (red)???or can you only do this mathematically if you know the plate voltage and current etc??Thanks for info
:::
::
:
Terry