Bias MA in Asteroid build

[deuce42]

Hi guys

I've built an asteroid style build using an existing diode rectifier power supply board with a slightly different bias circuit as the attached schematic shows here.

The transformer bias tap on the schematic is 50v but the bias tap on the transformer I am using is 45v. Currently the maximum bias MA I can't get with the bias pot turned up full is 35ma. I'd like to bias the amp hot at around 40ma. I realise this means I need to change the value of r53 (I did not use r67 as shown in the diagram). I'm just confused as to how to determine what to change it to? It currently is 56k but I am trying to understand whether I increase or decrease this resistor value and by how much if I want to get a bias range that will go up to about 40ma or slightly higher.

Could you guys educate me a bit?

Thanks very much

[JazzGuitarGimp]

To bias the tubes hotter, you need to get the bias voltage more positive (closer to ground). The easiest way to get there is to decrease the resistor that sits between the bottom leg of the pot and ground: it is currently marked as 53K to 56K. I would try 47K. I suspect that will get you into the range you're after.

Cheers,
Lou

[deuce42]

Thanks. I'll try 47k then. I understand that the voltage closer to zero is what I am trying to achieve.

Cheers

[KellyBass]

47k is exactly where I ended up.