What kinds of things blows fuses?

[TerryD]

There is a 100 watt 1971 fender bassman head that I want to sell for a fellow in town.  It's pretty beat up.  It's blowing fuses.  What things do that?  Could plugging it in without being hooked up to speakers do that?  Thanks, Terry

[HotBluePlates]

Excessive current draw blows fuses. That's it.

The challenge is finding the thing that pulls excessive current. "No speakers" doesn't do that typically; that's an issue of potential voltage spikes in the output transformer, and usually just kills the OT.

There is a 100 watt 1971 fender bassman head ...  It's blowing fuses.  ...

When? When it is turned on? When you play it? When you dunk it under water?

[plexi50]

When does it blow the fuse?
Flipping only the power switch on?
Flipping the standby switch on after power switch is on?

[Paul1453]

There is a 100 watt 1971 fender bassman head that I want to sell for a fellow in town.  It's pretty beat up.  It's blowing fuses.  What things do that?  Could plugging it in without being hooked up to speakers do that?  Thanks, Terry

You want to sell for a fellow?  In it's current fuse blowing state it will not fetch much of a price, and certainly is not of much value to this fellow.  Maybe you want to BUY this from the fellow and then fix it for yourself.  Ask him if he'd take $20 for it.  No, how about $30?  You might get yourself a deal.

[TerryD]

Thanks.  I was hoping to give him 200 and sell for 400 but apparently "It was just my imagination....once again"

Thanks,
Terry

[jjasilli]

FROM GEOFEX.COM . Tube Amp Debug page:


Fuses blow quickly for massive overloads, like AC shorts to a grounded chassis. They blow with a some time lag - maybe only a second or two, up to minutes, as the overcurrent gets closer to the fuse's actual rating. Anything that uses enough power to cause the AC line current to exceed the rating of the fuse will eventually cause it to blow.
It is important to remember that a fuse NEVER blows without something else being wrong. It could be that:

• fuse is the wrong rating - replace it with the correct rating
• power tube shorted
• rectifier tube shorted
• power supply filter cap failing
• Carbon trails on the output tube sockets between the plate lug and the other electrodes, especially the heater electrodes.
• power tubes have lost bias or biased incorrectly
• power section of the amp is oscillating at too high a frequency to hear
• there is an ac wiring short or high leakage
• power transformer is faulty
• choke (if present) is shorted/leaking to chassis
• output transformer is faulty
• AC power wiring or B+ power wiring is faulty/shorted

[eleventeen]

Paul1453 has the right idea. Try to buy it cheap.


The GEOFEX list jjasilli posted is the punch list.


The standard concern here is: If you know enough to fix this (it's fairly easy) then you shouldn't be asking the question. Please don't take my comment as an insult. It's a safety concern. The things that blow fuses are 99% of the time located in the highest power/voltage section of the amp.

[Colas LeGrippa]

remove the output tubes and power it on. if the fuse doesn't blow, replace the power tubes one is short.

[HotBluePlates]

... apparently "It was just my imagination....once again"

Not blowing fuses now?

[TerryD]

No. Getting 400 beaners as is.