Real McTube fuse

[MikeH]

I just pulled out the tonepad RMT I built many years ago and I noticed that it does not have a fuse on it. Which seems... well, dangerous, to say the least. Can anyone tell me what value fuse would be appropriate for this project, and how they determined that value?

Much thanks in advance.

[PRR]

All power comes through one 12V 0.5A transformer.

12V*0.5A = 6 VA (about 6 Watts).

Are you 230V or 120V wall-juice?

In Ann Arbor (surely 120V): 6VA/120V= 0.05A fuse.

You must round-up severely! Start-up surge, magnetizing currents, and other unknowns. I have seen a smaller transformer unable to run with less than 0.5A fuse. Still, worst-case 120V*0.5A is only 60 Watts, which can set fire, but isn't too likely.

> seems... well, dangerous, to say the least.

Actually not. Doorbell transformers in this size are routinely connected with NO fuse. Instead their high internal impedance (big sag) means they CAN'T suck big power and are unlikely to start a fire. I recently noted that several 12VA general-use world-fit units are stated to be "intrinsically limited".

[george]

Why bother?  All the Real McTube demos I've heard sound pretty ordinary to me, even if you are only after a low gain bluesy kind of sound.  If you want to do high voltage, try the GTFO by gtudoran.  Runs off 12v DC and and sounds like that SLO that you've been wanting to sell your grandmother for.

[antonis]

All power comes through one 12V 0.5A transformer.
12V*0.5A = 6 VA (about 6 Watts).
.................................................
Still, worst-case 120V*0.5A is only 60 Watts,

You confuse me, Paul..

If secondary's current capability is 500mA then primary's one should be 1/10 (at 120V with not counting any loss) and power should be 6W (idealy) so mains fuse should be a 50mA (practically a 100mA one)

If it's slow-blow type, IMHO he shouldn't worry about inrush current (even if he deals with toroidal transformer)

Or maybe I missed something on your answer..??