• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Need Fuse Values for 6922 Tube Premp, 6.3v & B+ Fuse Value

I wonder if someone can help me. I build one of GlassWare Audio Design's power supply's, the PS-1 and their Aikido Cascode preamp and they work perfect!

The Aikido Cascode preamp holds four 6922 tubes.

I would like to put a fuse for the B+ and one for the heater that goes to the tubes. I was wondering what fuse amp value to use on each. I would like an inline fuse in the Power Supply (PS-1) also.

Here is more data:

The PS-1 (Power Supply) was configured to output 150Volts (from the 230V transformer), and the winding for the heater puts out 6.3V

The Aikido Cascode was configured for the 6DJ8/6922 tube, it holds four 6922 tubes all pulling 6.3V each, and is configured to drop the 150V B+ down to 90V to the tubes.

I would like a general fuse for the PS-1 but don't know what value to use, then a separate fuse for the B+ going to the preamp and then a fuse for the heater wires (slow blow they recommend for the heater fuse) that go to the preamp but I don't know what value of fuses to install.

Can anyone let me know what values to use for each? I have asked but they don't answer my technical questions.

Thanks in advance!
Rob
 
Link may help you start the selection process. There is no 'general' fuse value to use - you do need to provide some technical effort of your own to detail the currents flowing in your circuitry - whether you then make a guess or get a suggested value provided to you or go further and do a good technical assessment is up to you.

http://dalmura.com.au/projects/Valve%20amp%20fusing.pdf
 
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To choose a fuse you need to consider what it is guarding i.e what fault conditions you wish to deal with. Obviously, the fuse must cope with the normal current flow and any start up extra current.

It is unusual to fuse a heater supply. It is difficult to fuse a heater supply. It is usually unnecessary to fuse a heater supply.