Hi stax experts,

I measured my t1w bias voltage, the pro bias port is 420v and normal bias is about 150v, is this normal or something needs to be replaced? Thank you. 

9 hours ago, qqiao said:

Hi stax experts,

I measured my t1w bias voltage, the pro bias port is 420v and normal bias is about 150v, is this normal or something needs to be replaced? Thank you. 

if you are using a multimeter with a 10Mohm input impedance then you will not measure the actual voltage. The stax bias output is very high impendence i.e. provides very very little current and so even the current draw of a 10Mohm multimeter will load down the bias and you will measure lower than expected. Either you need a meter with a Gohm or higher input impedance at 1000V or you need to measure before the current limiting system on the bias output. For example the golden reference HV power supply bias circuit has a 4.7Mohm current limit resistor just before the output so you need to measure before that limiting resistor and of course be careful because if you multimeter can't handle 580V or you touch the probes etc you will get a non-current limited 580V DC shock which is not going to be good for you.

incidentally I get about 378V DC at the socket on my diy T2 (pro bias only) into a 10Mohm meter BUT this value is going to be very dependant upon the value of the current limit resistor in the bias circuit. So if you amps current limit resistor has a lower value then 420V is not necessarily unrealistic.

 

Edited June 4, 20224 yr by jamesmking

Hi Jamesmking,

Thank you very much for the details. The t1w has an adjust resistor for one pro bias port, so it can give 3 different bias voltage, a very versatile amplifier. 

https://i.imgur.com/Dz9hxo6.png

I found the schematic fo 007, the bias circuit should be similar as t1, actually I don't fully understand how it can get 580v voltage, the output from the transformer only provides 270v, it looks like a half wave rectifier circuit.

It's a voltage divider feeding a voltage doubler

understand, thanks very much for the explanation.