Safe to use 6L6/5881 with 120mA rated PT?

[elipsey]

Thermistors are commonly and successfully used for just this purpose i.e surge control in millions of pieces of equipment. The down side is you have to let them cool off between cycles.

What happens if I don't?

[nickb]

What happens if I don't?

You get a current surge, very similar in magnitude to not having one as all.

[elipsey]

You get a current surge, very similar in magnitude to not having one as all.

Thanks. So I suppose that if the user flipped the power or standby on and off repeatedly and quickly, the thermistor would not help. They proabably shouldn't be doing that with any tube amp I guess?

[nickb]

Thanks. So I suppose that if the user flipped the power or standby on and off repeatedly and quickly, the thermistor would not help. They proabably shouldn't be doing that with any tube amp I guess?

There's always one....

I suppose you could use a quick blow fuse along with the thermistor if you were really concerned about it. If you get a surge then it blows and protects against any more. I think it might be quite tricky to get the optimum value. It would not be my personal choice, it would sure tick the pants off me if the fuse blew every time I accidentally left the standby closed

If it really bugs you can use a MOSFET (or relay) to reliably switch the HT to avoid surges. With a MOSFET you could even extend that to make sure it limited the voltage to the safe range too. I fear we may be overthinking it now, after all there are plenty of amps that have run for decades with no anti-surge measures.

[elipsey]

So this was a pretty cheap and easy way to build a power supply, and with a multi-tap transformer I can have any plate voltage I want. The problem is I built it for myself as an experiment, but now I'm thinking about giving it to my cousin so I don't want it to embarrass me by breaking!



Edit: I should add that I have now totally changed amps in this conversation, but I'm looking for generally applicable approaches to power supply design and reliability here.

[nickb]

So this was a pretty cheap and easy way to build a power supply, and with a multi-tap transformer I can have any plate voltage I want. The problem is I built it for myself as an experiment, but now I'm thinking about giving it to my cousin so I don't want it to embarrass me by breaking!

[ATTACH=CONFIG]40270[/ATTACH]

Edit: I should add that I have now totally changed amps in this conversation, but I'm looking for generally applicable approaches to power supply design and reliability here.

I think it was a perfectly acceptable way to do it. And better than most. I don't think you have anything to fear (unless your cousin is the one of the one's we were just talking about).