Express blowing fuses

[DerStever]

My clone which is part Ceriatone (PS and Boards) has been running great ever since Allyn found the hum issue and I found the hiss problem. However at a gig last weekend it popped one of those dinky 2amp mini fuses - I thought it was because the fuse was a quickblo not a slowblow so I put a slow blow in and played the rest of the gig no problem.

During some "experiments" today with volume off I had to turn the amp on and off without the HV supply engaged and I blew a slowblow in the process. I'm wondering if I don't have some issue somewhere in the amp doing this. I had been using it every week at practice + on my own practices without any problem - the only thing new has been swapping out the PI tube from a Westinghouse Mullard 12AX7 to a Mullard 12AT7 for giggles - Ive since put the old tube back in but I'm not confident thats the problem.

I already had a problem (blew fuses) with a Heybour power tranny in the beginnning of the build and Mojo took it back - said it was defective - they sent me this one. Does anyone have some tests I could run to isolate the problem - as I said - its intermittant and because of this I'm tempted to do the unthinkable and put in a 2.5 amp fuse or a regular size in-line fuse instead just to see if I can find the problem.

Help!

[paulruby]

2A is on the hairy edge. You can increase to 2.5A. I've run into this, too... Although I spec 2A for my 50W amp builds, about half of them really need bumped to 2.5A.

[DerStever]

Thanks Paul - I will.

[Elcabong]

A quick test could be to measure the voltage drop across the 1k resistor and calculate the current draw at that point. If it appears too high, you can then measure across the 18k2, 9k1 and so on and maybe isolate the problematic section.

[lastwinj]

what are the specs on the power tranny? larger trannies, even if the current draw from the amp isnt as much, will sometimes need a larger fuse, that is used for a larger size/wattage amp.

i am using toneslut trannies for a current build, and i am using a 3A sloblo due to its overspec.

germ

[John C]

DerStever (or anybody here),

Would you mind posting your findings & results with your (larger) fuse-size testing and current testing experiments?

Thanks,

John

[DerStever]

I havent had anymore fuses going - but I plan to buy some 2.5s soon. INA sounds really great with that Celestion Alnico Gold - I'll have some recordings soon - we are in the studio now and I'm using INA exclusively for both songs.

[Roe]

2A is on the hairy edge. You can increase to 2.5A. I've run into this, too... Although I spec 2A for my 50W amp builds, about half of them really need bumped to 2.5A.

But should a 240v amp have 1A fuse?

[paulster]

But should a 240v amp have 1A fuse?

It should, but if you're using big transformers like the Toneslut ones then you'll probably want to go up to 1.5A in the same way that a lot of 120V users have gone up to 2.5A to avoid fuses popping.

[Roe]

thanks!

my express works very well. i will do more testing with different tubes after I get back from vacation

[DerStever]

I did go to the 2.5 and all problems have ceased!