How to determine the needed B+

[HMV130]

Hello to everyone,
surfing on the net I have not found anything about "how to determine the needed B+" given a amp schematic.

For every technical article that I managed to find the B+ was always a given parameter in order to determine i.e. plate voltage of the rectifier etc.

Moreover in many vintage schematic there is no specification about the high voltage secondaries of power transformers nor the (needed) B+ coming out from the filtering circuit.

Could someone be so kind to explain me how to how to determine the needed B+ from a amp schematic (i.e. the one attached - what is the voltage that should be measured at the end - to the 6NS7GT tube - of the CRC filter circuit)?

Thanks

 

[JonSnell Electronic]

The best you can do is look at the HT capacitor voltage rating and subtract say 25% for safety margin then work backwards to the transformer. In this case the capacitors are 450V so call it 300V which would fall in line with the maximum HT for the 6V6 valves of 315V.

 

[rayma]

what is the voltage that should be measured at the end - to the 6NS7GT tube - of the CRC filter circuit)?

Probably from 250VDC - 300VDC. I built a related model of this amp in the 60s as my first hi fi project.

 

[DF96]

The quick answer is no, it is not possible to work back from a circuit (giving no voltages) to a rail voltage. The best that can be done is to have a wild guess, based on experience - and assuming the circuit designer knew what he was doing.