What fuse in 230v amp?

[Oddvar R]

Hi, what fuse do I use in European Dumble 230v? Schematics says 5A slo blow, is that the value or is otherwise?

[martin manning]

Reduce it by half to 2.5A slow blow.

[Oddvar R]

Thanks...

[norburybrook]

I put 2A slow blow in my Dumbles




M

[Oddvar R]

I put 2A slow blow in my Dumbles




M

Any reason why you choose that value?

[martin manning]

The fuse should be as small as possible, but not too small, i.e. not so small that it opens on power-up due to the initial current surge. If Marcus is having success with a 2A fuse operating in UK at 240V, then you can probably use that value too.

[norburybrook]

I put 2A slow blow in my Dumbles




M

Any reason why you choose that value?

I've no idea I'm sure when i started building I saw/read something that mention 2A fuses for the mains so I've been using them ever since on my 50 and 100w ODS amps. I've had no issues with any of them using that value.

MC

[erwin_ve]

3A for a 100w, 2A for a 50w when in 230-240 area.
It's better to slightly go above 1/2 110v rating. The inrush current can take a 1/2 rating fuse when in 230-240v area.
Marcus: You lucky bastard

[Guy77]

Hi. I have also used 1.5A - 2A fuses on 230v - 240v builds of 50 watt dumble style amps, as Erwin has mentioned, with no issues.

Cheers
Guy

[norburybrook]

3A for a 100w, 2A for a 50w when in 230-240 area.
It's better to slightly go above 1/2 110v rating. The inrush current can take a 1/2 rating fuse when in 230-240v area.
Marcus: You lucky bastard

Hmm, I've got a couple of 100w amps out in the field getting hammered regularly should I get them back and fit 3A fuses? Had no issues with any of them.


M

[erwin_ve]

Marcus, I think it is ok. It's the inrush current that can take out the fuse, so when you switch the amp on. If your amps dont have this problem dont bother.

[didit]

Yes. If it's worked so far, should continue so. Avoid bad substitutions, and include a spare fuse (or two) of the correct type.

Best .. Ian

[donvan]

For the sake of someone who stumbles onto this thread looking for the answer to their fuse questions I think that the output power tubes need to be part of the discussion. I don't think it's enough to just say that the output is 50 or 100 watts so use fuse size x.

Also, it might be a little misleading if we say something like "I use 1.5 amp fuses in all of my 100W builds." That may be fine if all of that persons 100W builds used 6L6 power tubes. However, EL-34 output tubes draw a lot more current than 6L6s. So. you should probably also mention the power tubes you are using as well as your fuse size.

From what I am seeing in the file section schematics, Dumble used 5 amp slow flow fuses for 100W, EL-34 amps and he used 3 amp slow blow fuses for 100W, 6L6 amps.

So, I guess what I am trying to say is that I'm a little nervous hearing people suggest that 1 size fuse will work for all 100W amps.

I think I prefer Martin's advice (in my own words): For a 230v amp use a fuse that is 1/2 the value of what is called for the in the 120v schematic.

[norburybrook]

For the sake of someone who stumbles onto this thread looking for the answer to their fuse questions I think that the output power tubes need to be part of the discussion. I don't think it's enough to just say that the output is 50 or 100 watts so use fuse size x.

Also, it might be a little misleading if we say something like "I use 1.5 amp fuses in all of my 100W builds." That may be fine if all of that persons 100W builds used 6L6 power tubes. However, EL-34 output tubes draw a lot more current than 6L6s. So. you should probably also mention the power tubes you are using as well as your fuse size.

From what I am seeing in the file section schematics, Dumble used 5 amp slow flow fuses for 100W, EL-34 amps and he used 3 amp slow blow fuses for 100W, 6L6 amps.

So, I guess what I am trying to say is that I'm a little nervous hearing people suggest that 1 size fuse will work for all 100W amps.

I think I prefer Martin's advice (in my own words): For a 230v amp use a fuse that is 1/2 the value of what is called for the in the 120v schematic.

good points I think when I started I hadn't come across a thread like this so it's all good information, well for me at least Fortunately from a safety concern using too small a fuse isn't a safety issue.

M

[martin manning]

Good point, Donvan. The initial current surge is mainly PT magnetizing current, reservoir caps, and filaments. It would be reasonable to assume that the first two are proportional to the output power, but the filament current is 0.6A more per tube for EL34 vs. 6L6. That's 0.6A per tube steady-state, but probably 3x that when the filaments are cold, so say 1.8A/tube. Referred back to the primary that's 120/6.3*1.8, or 0.095A. So for a 100W amp, I'd add 0.38A to the fuse rating for EL34.

True enough Marcus, but you don't want the damn fuse blowing for no reason when you switch on.