Digital Bias Meters

[Scar_Begonia]

Right now I am building a Bob Latino vta120 kit. Before I put the sockets in the front for testing bias voltage I had an idea....
On the bay there is someone that sells digital bias meters that plug into the sockets and display the bias voltage. They are sold do $80! I know from doing some mods for my car that you can buy dc voltage meters, just drill a hole and connect positive and negative wires and the voltage is displayed. The hole for these meters is the same size as the holes inthe amp chassis. My question is; would these work are bias meters? They only cost like $12 and I figure all I’d have to do is put them in and attach the bias positive and ground the other size just like you would do with a volt meter. Does this idea work? Or is there something special I am missing that the expensive meter have that the cheap ones for the car doesn’t? Of course I can’t find a pic of the expensive ones now but these are the ones I want to buy and install

 

[Ken Boyd]

you could buy one and then use it instead of your DMM and see it if works.

 

[gadget73]

It quite likely powers from the source it measures, so it might not read at 1.5v or whatever those bias at.

A voltmeter that has an external power source plus two leads for monitoring a voltage would get it done though. An analog meter would also likely work fine.

 

[Scar_Begonia]

you could buy one and then use it instead of your DMM and see it if works.

I actually have one. I was nervous about hurting the amp trying it.

 

[Scar_Begonia]

It quite likely powers from the source it measures, so it might not read at 1.5v or whatever those bias at.

A voltmeter that has an external power source plus two leads for monitoring a voltage would get it done though. An analog meter would also likely work fine.

That makes sense, except if it’s a meter telling you what voltage your car battery is running at, shouldn’t it be able to dip below 12v? I was thinking it probably only needs some miliamps to work.

 

[s-petersen]

You really need a 3 wire 9.99v meter 2 of the wires are power, and the 3rd is the sensing voltage. I blacked out the decimal point.

 

[Scar_Begonia]

You really need a 3 wire 9.99v meter 2 of the wires are power, and the 3rd is the sensing voltage. I blacked out the decimal point.

The image didn’t come through.

Are there three wires connected to the socket in the inside and that’s why I need three wires? I haven’t gotten there yet in the build.

 

[Scar_Begonia]

Here is a picture of the ones sold on the bay.... how do these work? They look just like the ones at the auto store

 

[s-petersen]

http://audiokarma.org/forums/index.php?threads/citation-ii-hack.471242/ Citation II picture
you need 2 wires for power to the meter, and 1 goes to the bias point

 

[gadget73]

That makes sense, except if it’s a meter telling you what voltage your car battery is running at, shouldn’t it be able to dip below 12v? I was thinking it probably only needs some miliamps to work.

I'm sure it goes below 12v, but I doubt it runs as low as the bias voltage in a typical tube amp. If this biases like an original ST-70, thats 1.56v.

The type of meter Scott suggests would certainly do it though.

 

[kward]

how do these work?

It uses a separate power source.

Quote from the details of that listing, italics and color added for emphasis:

"Removable when not in use , keeps octal sockets stock doesn't alter using inputs at the octal sockets .
here is a visual led bias indicator kit , it comes with a pair of digital led's and everything needed and is pre-wired for installation does have some solder points and installation of a powerpak ."