[tab10672]

I have a couple old trf's which some have a c batt post and some do not. on the scematics without it the transformer just jumps across where the c batt would be and leads back to a-, so my question is... Is the c batt a necessity or can you bypass it from the trans (c-) to a- and omit it? Thanks Todd

[BrendaAnnD]

If it requires a C battery, you will need to use one. This is bias for the tubes, and without it, they will run the wrong class and either distort the signal or keep it from passing completely.

[keithw]

The set will work vastly better with a C battery. The B current will be lower and it will sound better. Depending on the tube it will be from -4.5 to -9 volts DC. I have had good luck with -4.5 from 3 c size batteries in series. It draws virtually no current so they will last for a very long time.

To be technically correct the C voltage, grid bias, should be negative enough to keep the grid from ever going positive in relation to the cathode but not so negative as to cut off the plate current entirely.

keithw

[TA Forbes]

Depending on the set the C battery is usually vic -3 to -4.5V. You must connect it this way and not as a positive voltage at the grid of your tubes.

[tab10672]

Thanks for the info. I ask only because one set I own has a jumper between the c posts and I didnt want to power it untill I was sure. Thanks, Todd

[Alan Douglas]

If the B+ is less than 70 volts or so, you can run 01As with no C bias.