4V Tentlabs filament supply

[ianc13]

Hi,

I have a quick question about wiring up a Tentlabs filament supply.

The supply is 4V and looking on the Tentlabs page for fitting instructions it seems that 'ground' side of the supply should be connected to the top of the cathode resistor for auto bias.

Would I need to look at biasing my output tube slightly differently in this instance - i.e. shifting the bias by 2V so that the filament is bias(-31V) + 2V at one end and bias - 2V at the other end.

This is on a Chinese PX25 which should be biased at around -31V for 400V/62.5mA operation.

Thanks,

Ian

 

[pmillett]

Technically, yes, it will shift the bias. But +/-2V on a 31V bias point is inconsequential; the tube characteristics will vary more than that. So you really don't need to change anything.

Pete

 

[ianc13]

Many thanks Pete, most appreciated.