prr meter

guys im using a 1 milliamp jewel meter for my varimu.  it barely causes my meter to move (.05ma) when on.  on should be full cathode current.  any advice other than adjusting the trimmer (its wide open)?

just found this.  now im confused...
nydave said...I said  microammeter, not milliammeter.The tube is never going  to draw enough current
to make either of these meters do more than barely twitch.

i though prr recommended milli

Replace trimmer with 100 ohm resistor.

Use good volt meter to read DC voltage.

Refer to your signature.

How much?

did that  and so 0.09v=.9mA(100r)  very nice very clean.

so when i hooked up my DVM in current mode i got a beutiful .90mA that dropped to anywhere from .30 to .50 during compression.

  so when i switched this dvm out for my 1mA analog meter http://www.mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMtFJx2zDaGuWHe0QOuVkjToNMC7PBfPjuI%3d
i get barely a twitch.  i don't think the meter is broken cause i took one side of the led in the psu out and the current on the analog meter was .75mA.  spent the last hours trying to figure out why they dont agree when in circuit.  does the ohmage listed for this meter in the mouser catalog mean anything? (it says 1.1k) do i need a shunt or something?  ahhhh

ok so i bought another jewel meter just incase the first was broken.  same thing.  anyone using a meter that they recommend that works here?

> so 0.09v=.9mA(100r)

Should be more?

I estimated typical 6mA for 12AU7 at 100V supply; is that the tube and supply you are using?

But that's not a big problem.

Does sound go through? Does it squash?

> 1mA analog meter ... barely a twitch.
> led in the psu ... meter was .75mA.

Incredibly odd. (Is the LED current really as low as 0.75mA? 7mA would be more typical; I'm wondering if you got a mis-marked 10mA meter?)

I assume you tried both ways; that it isn't just slamming the pin trying to go "below zero". The terminals should be marked, but mistakes happen. However the pin is usually a bit left of the zero, so you'd notice it trying to go the wrong way.

> does the ohmage listed for this meter in the mouser catalog mean anything? (it says 1.1k)

Yes, and I'd expect more like 100-200 ohms on a 1mA movement. In this case 1K in the cathodes "matters". I'd still expect it to "work": show a clear indication when idle and dip when flogged.

PRR said:

> so 0.09v=.9mA(100r)

Should be more?

Click to expand...

its 4.6ma out of the cathodes. 0.9ma after the 100r resistor

PRR said:

> so 0.09v=.9mA(100r)

I estimated typical 6mA for 12AU7 at 100V supply; is that the tube and supply you are using?

But that's not a big problem.

Does sound go through? Does it squash?

Click to expand...

yes it sounds f$%#%!ing great

PRR said:

> so 0.09v=.9mA(100r)

> 1mA analog meter ... barely a twitch.
> led in the psu ... meter was .75mA.

Incredibly odd. (Is the LED current really as low as 0.75mA? 7mA would be more typical; I'm wondering if you got a mis-marked 10mA meter?)

I assume you tried both ways; that it isn't just slamming the pin trying to go "below zero". The terminals should be marked, but mistakes happen. However the pin is usually a bit left of the zero, so you'd notice it trying to go the wrong way.

Click to expand...

yes both ways.  when i put the cathodes directly into the circuit (4.6ma) it slams right.  flip polarity it slams left.

PRR said:

> so 0.09v=.9mA(100r)

> does the ohmage listed for this meter in the mouser catalog mean anything? (it says 1.1k)

Yes, and I'd expect more like 100-200 ohms on a 1mA movement. In this case 1K in the cathodes "matters". I'd still expect it to "work": show a clear indication when idle and dip when flogged.

Click to expand...

so im done with the jewel cheapy.  i bought this meter

looks better and hopefully it matches my multimeter mA readings.

1mA meter with 1.1K resistance must drop 1.1V at 1mA.

You have 4.6mA total. You want 1mA to flow in the meter, and the other 3.6mA to flow in the shunt, when there is 1.1V across the shunt.

1.1V/0.0036A= 305.5555 ohms.

Start somewhat smaller. If the needle goes to 9/10 of full scale, it "works". The tube will drift with age and replacement. Also the added resistance (compared to 100 ohms) will reduce tube current a bit. Leave some room for drift. 270 is a good common resistor value.

popped in the NOS meter and everything works brilliantly .  thanks all

ill still try the added resistance on the jewel so that i can use this meter some other time (and to understand the R rating on mA meters)

so this NOS meter works as my DMM worked, no extra resistance needed.  does that mean its built into the meter?