I swear baby, this has never happened before (please help me, Crack won't work)

[Todd R]

You guys might want to measure the resistance value of that first 270 ohm resistor to make sure it didn't drift when it was connected wrong. I would think it would hold up OK, but it's easy to check. The two different fuse problems could be from different causes, e.g, the fuse blowing when the amp isn't even turned on indicates a problem in the IEC socket or power switch wiring, while a fuse that blows after an hour usually indicates that it was previously stressed and just finally let go.

FYI, I checked and it did not blow when plugged in but amp left off, so it's not an IEC problem.

Resistor checks fine at 270 ohms.

[Doc B.]

It's possible that the 1/2A Slo Blo fuse could be marginal. If all the resistance checks are still good you could maybe try a 1A. I've seen the situation happen in the past where we spec the smallest fuse that holds OK on the prototypes, and then end up going up one size because we see the occasional failure in the field during the startup current surge. It could be that there are variations in how much and how fast various tube heaters pull current when they start up.

[Dr. Toobz]

You guys might want to measure the resistance value of that first 270 ohm resistor to make sure it didn't drift when it was connected wrong. I would think it would hold up OK, but it's easy to check. The two different fuse problems could be from different causes, e.g, the fuse blowing when the amp isn't even turned on indicates a problem in the IEC socket or power switch wiring, while a fuse that blows after an hour usually indicates that it was previously stressed and just finally let go.

Doc,

I get a reading of ~320 ohms on that resistor as opposed to 270. My meter is really old and cheap, so it's possible that could be part of it, but usually, the resistances are within 5%. That would be 18.5% off. Are these 20% tolerance or something?

I visually checked my new 500mA fuse, and it looks like new. So I think that the last one indeed became stressed and just "let go." The local Rat Shack has a bag of .5A ceramic fuses for something like $1.99, so this was easily fixed.

EDIT: Just to clarify, I cannibalized the .5A glass fuse that came with my Seduction for the Crack, and replaced that with a ceramic fuse in the Seduction. Can't really "visually inspect" a ceramic fuse..... :-)

[Todd R]

It's possible that the 1/2A Slo Blo fuse could be marginal. If all the resistance checks are still good you could maybe try a 1A. I've seen the situation happen in the past where we spec the smallest fuse that holds OK on the prototypes, and then end up going up one size because we see the occasional failure in the field during the startup current surge. It could be that there are variations in how much and how fast various tube heaters pull current when they start up.

Slo Blo? The one it came with & the ones I've been blowing are fast blow. Ok, will go up to 1A if I can't find 1/2 amp slo and let you know here in a couple min.

[Todd R]

Alright, found a 1.6A fuse in my arsenal and gave it a try.
The amp is on now. I'm going to leave it running with an iPod on repeat while I work on my kitchen floor project and check it periodically.
What would be the maximum fuse size that would be safe to put in this amp?
Thanks,
TR

[Doc B.]

I would first try a 1/2 A slo blo (I thought that was what we had in stock here) and if that doesn't hold try a 1A slo blo. We can mail some to you if you like.

[Todd R]

I would first try a 1/2 A slo blo (I thought that was what we had in stock here) and if that doesn't hold try a 1A slo blo. We can mail some to you if you like.

That would be cool if you could since I've already made 2 trips to the "shack" today.

[Todd R]

Got the fuses, thanks.
TR