Blown fuse

barryswanson

New member
So I switched on my brand new VH4 and the mains fuse blew. I checked it over for any obvious faults and replaced the main fuse. Played it for an hour an all channels with no problems checked power tube fault lights and none where lit. What would cause that? I am an electrician by trade and I understand a short or excess current draw would blow the fuse but amps are not something I work on. I’d like to note that my amp is a 230v model and our nominal wall outlet voltage is 240v in Australia but can vary from anything between 230-250v depending time of day etc. Would it be wise to swap a couple of the transformer wires around to the 240v spec as per the service manual, or leave it as it is?
 
Well, I'll let someone with more direct VH4 experience than I answer, but I'll take a preliminary stab.

With the blown fuse, I'd guess that if it was the first time you'd turned the amp on, maybe the inrush of current to the filter caps combined with the higher than expected voltage might've caused the fuse to blow. If you haven't had any more problems with blowing fuses, and assuming that you replaced the blown fuse with the exact rating for voltage and current (since you're an electrician, I'm sure you did), I wouldn't worry about it.

As for changing the transformer to the 240v winding, yes, I would do that if it were mine. Since you're local voltage is 240v, leaving the amp set to 230v is going to subject all its parts to an additional 5% higher voltage, closer to 9% if the local supply goes up to 250v. That's putting extra wear on all the parts. Best case is that you wear out your tubes faster, but you'll also be more likely to blow capacitors, resistors, relays, logic ICs, and even risk the transformers and especially the tubes.

Having said that, Diezels are incredibly tough amps, built like tanks, and are definitely made of the highest caliber parts. While I'm sure they can withstand as much abuse as any and more than most, personally, I just wouldn't chance it.
 
Not to take away from Peters point, which of course is a great point.

But I have found fuses tend to wear out over time, especially when there are high surge loads ( such as when you hit the power switch on and amp, and all those big caps are filling, very close to an short for a small amount of time) Some amps have a ICL (inrush current limiter) that slows the current on startup.
 
That’s plausible, but I learnt something today that I didn’t even though. Australia is 230v not 240v I found this;

The Australian Standard AS 60038 states the nominal mains voltage as 230 V +10%, – 6%, giving a range of 216.2 to 253 V.

Makes me wonder than why all my Mesa Boogies are marked 240v is it because it can get up to 250v? I myself have measured 250v plenty of times and more often measured around 230v. But right now this is what I’m getting. Given that information do you think I should still wire it up to 240v Peter?

 
FWIW, I would. Running a few volts under is much easier on the amp than running a few volts over. Of course, I'll defer to Peter's direction.
 
All sorted, thanks to Peter for his advice. Your really can’t get better customer service. Being able to speak directly to the guy who designed the amp is truely remarkable. Now I know what you guys where on about.
 
Peter's customer service is the best in the business. Completely world class operation in every aspect: design, quality, and service. Hope you're enjoying that beast of an amp!!
 
I sure is man! I love this thing. Channel 3 is what I bought it for and it doesn’t disappoint. Even sounds good a bedroom volume.
 
Good to hear! I love my Herbert!! It sounds great no matter what volume I'm at, and, oh... it can get LOUD! I've had it a little over a year now and I still find new sounds in it every time I play. One of these days, I'll get a VH4, too. The Paul looks really interesting, too, as does the Big Max. Diezels are definitely addicting!! Absolutely modern classics!
 
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