Hey all...
So I have re-caped the amp, replaced the bad stuff and I have came to a bit of question... As I am in Europe and use 220-240V lines and select 240V at the selector always, what kind of fuse should I put into the amp, it calls for a 2.5 amp slo-blo (written under the fuse holder) but it doesn't say the voltage it needs, but on the left corner of the fuse holder amp says 117 volts 2.3 amp 60 cycles and how is that possible when amp is running on 220V?
I don't know many things about tube amps, but i laughed at myself for not solving that problem.
So I have re-caped the amp, replaced the bad stuff and I have came to a bit of question... As I am in Europe and use 220-240V lines and select 240V at the selector always, what kind of fuse should I put into the amp, it calls for a 2.5 amp slo-blo (written under the fuse holder) but it doesn't say the voltage it needs, but on the left corner of the fuse holder amp says 117 volts 2.3 amp 60 cycles and how is that possible when amp is running on 220V?
I don't know many things about tube amps, but i laughed at myself for not solving that problem.
The Export model has either multiple taps or straight 230volts. The mains fuse should be 2.5A slow blow for 230volts and 4A for 117v.
Don't forget to disconnect the killer capacitor on the hum phase switch!
Don't forget to disconnect the killer capacitor on the hum phase switch!
I have been searching around google but can't find one, do you where they maybe sell them in EU?
What fuses do you find? General purpose fuses sold in the EU should have suitable voltage ratings. I would think 2.5A slow blow fuses are common. I expect they will have ratings like 250v. There is no voltage to match. You just need fuses rated for your mains voltage or higher. Do you not have fuses in your power plugs there in general? Use the same kinds of fuses you would use for a home appliance or a radio or TV set.
They are called T5A 20mm Cartridge fuse. They are rated at 250volts.
Here is an example; S505-2.5-R | Cooper Bussmann S505 2.5A Ceramic Cartridge Fuse, T, 5 x 20mm | Cooper Bussmann
Here is an example; S505-2.5-R | Cooper Bussmann S505 2.5A Ceramic Cartridge Fuse, T, 5 x 20mm | Cooper Bussmann
When run on 117V it sucks 2.3 Amps. They do not tell you what the current is when the PT is wired and fed with other voltage.
But you can work it out from Basics.
I have a 240 Watt heater under my desk. On my 120V power it obviously must suck 2 Amps. (120V*2A= 240 Watts.) The same heater is sold globally. The one for 240V lands must obviously suck 1 Amp. (240V*1A= 240 Watts.) If they make one for the 100V power in parts of Japan, it would be scaled to suck 2.4 Amps.
Therefore a "117V 2.3A" rating translates to "234V 1.15A".
We can also work back from the actual amplifier. The four big bottles and all the little ones take about 30 Watts of heater and plate power. The power bottles' plates probably idle somewhat below Pdiss(max), say 18W each or 72 Watts. At FULL Roar this is a 80-100 Watt output amplifier. Tube amps do not run much over 50% efficient. So when screaming the plate input power must be near 200 Watts. There is additional loss in PT.
Counting on thumbs, the Dual Showman idles at 100W and roars at 240 Watts.
At 117V this is just over 2 Amps. "2.3A" allows for some margin. 2.5 Amps is the next-up standard fuse size, though actually 3A is far more common in the store and in most older amps.
At nominal 234V this would be just over 1 Amp. A 1.5A fuse is a safe bet.
In the US, 1.5A is a standard value. EUR has different customary values. However the Fender fusefolder is scaled for the "3AG" series fuse developed in the US. So you may be offered a 1.5A. Littelfuse also lists 3AG slo-blow in 1.6A and 1.8A, which are 2nd choices for 240V lands.
When working the fuse has NO voltage. But when the fuse ruptures, it is harder to stop high-voltage than low voltage. This affects fuse size and cost. So there are two general everyday fuse ratings: 50V for cars, and 250V for wall-power. You want the 250V. (Even if you lived in 117V land.) Don't worry that your "240V" may some days be 255V. The fusemakers obviously allow for large line variation; "250V" nominal rating is to differentiate this series from, say, the 25,000V fuse my neighbor just blew on his power feeder, or the 600V fuses for industrial use.
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Official Dual Showman spec, for the USA model (117V) is:
Since it´s not a commonly available value, use immediate next higher, so 1.5A .
Mind you, it MUST be a Slow Blow or T(imed) type fuse, or it will "nuisance blow" often just on the turn on surge.
Some call them Surge fuses, for that reason.
This is a regular fuse, has only a thin wire inside and nothing else, will blow in a very short time, since it has very low mass:
This is a slow blow one (more expensive than plain ones); it has added mass inside (thicker spiral wound wire or even a ball of lead and a small spring) so it takes longer to blow and survives the initial current surge (a fraction of a second):
left to right, cheapest to best.
So 230V mains shoukd scale that to 1.25A .
Since it´s not a commonly available value, use immediate next higher, so 1.5A .
Mind you, it MUST be a Slow Blow or T(imed) type fuse, or it will "nuisance blow" often just on the turn on surge.
Some call them Surge fuses, for that reason.
This is a regular fuse, has only a thin wire inside and nothing else, will blow in a very short time, since it has very low mass:
An externally hosted image should be here but it was not working when we last tested it.
This is a slow blow one (more expensive than plain ones); it has added mass inside (thicker spiral wound wire or even a ball of lead and a small spring) so it takes longer to blow and survives the initial current surge (a fraction of a second):
An externally hosted image should be here but it was not working when we last tested it.
left to right, cheapest to best.
But I think the OP is looking to find some voltage rating on the fuses, and doesn;t realize they don't come in 100, 200, 300, 400 volt ratings like caps do.. There are of course voltage ratings, but he needs 250v fuses rather than 32v fuses.
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