Fuse rate to use 5E3 in EU

tweed · 10-31-2009, 04:27 AM

Hi all,

I'll back to Europe with my tweed in 2 days. I was advised that I should
change the fuse type from 2a 250V to 1a 250V, what would be more
appropriate "slow blow" or "fast blow"?

Thanks

tubeswell · 10-31-2009, 05:41 AM

multiply volts with amperes (for each winding) and you get VA. Sum up the VA values and you get the whole VA of the secondaries. Divide that by the mains voltage and you get the primary amperage. Take the nearest value and multiply by two.
For instance
PT:
650v x 70ma = 45.5va
6.3v x 2a = 12.6va
5V x 2a = 10va
68.1 va altogether

68.1va / 240v = 0.29a

Match to .25A and multiply by two = 0.5A mains fuse.

Somebody's bound to correct me if I'm wrong

Albert Kreuzer · 10-31-2009, 09:45 AM

Tweed,

does your amp have a voltage selector? Set it for 230V (or 240).

2A x 115V = 230VA
1A x 230V = 230VA

So 1A is what you need.
If you are using a stepdown transformer, leave the original 2A fuse in there.

Tubeswell, your calculations are correct, but a cranked amp could draw more than 140mA on the B+ and take out a .5A fuse.

Slow blow fuses for all tube amp mains.

Cheers,
Albert

tweed · 10-31-2009, 02:37 PM

The VAC is 220V and my power transformer primary has 220, 230, 240v taps.
So, 1A 250V slow blow will be fine.

I thought that fast acting would be better, but I understand they may be to sensitive.

Tks guys

10-31-2009, 04:27 AM	#1
tweed Member Join Date: Oct 2009 Posts: 21	Fuse rate to use 5E3 in EU Hi all, I'll back to Europe with my tweed in 2 days. I was advised that I should change the fuse type from 2a 250V to 1a 250V, what would be more appropriate "slow blow" or "fast blow"? Thanks

10-31-2009, 05:41 AM	#2
tubeswell Supporting Member Join Date: Feb 2007 Location: Wellington NZ Posts: 2,661	multiply volts with amperes (for each winding) and you get VA. Sum up the VA values and you get the whole VA of the secondaries. Divide that by the mains voltage and you get the primary amperage. Take the nearest value and multiply by two. For instance PT: 650v x 70ma = 45.5va 6.3v x 2a = 12.6va 5V x 2a = 10va 68.1 va altogether 68.1va / 240v = 0.29a Match to .25A and multiply by two = 0.5A mains fuse. Somebody's bound to correct me if I'm wrong __________________ Building a better world (one tube amp at a time)

10-31-2009, 02:37 PM	#4
tweed Member Join Date: Oct 2009 Posts: 21	The VAC is 220V and my power transformer primary has 220, 230, 240v taps. So, 1A 250V slow blow will be fine. I thought that fast acting would be better, but I understand they may be to sensitive. Tks guys Last edited by tweed; 10-31-2009 at 02:50 PM.

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10-31-2009, 09:45 AM	#3
Albert Kreuzer Senior Member Join Date: May 2006 Posts: 287	Tweed, does your amp have a voltage selector? Set it for 230V (or 240). 2A x 115V = 230VA 1A x 230V = 230VA So 1A is what you need. If you are using a stepdown transformer, leave the original 2A fuse in there. Tubeswell, your calculations are correct, but a cranked amp could draw more than 140mA on the B+ and take out a .5A fuse. Slow blow fuses for all tube amp mains. Cheers, Albert

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