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Don Pearce[_3_] Don Pearce[_3_] is offline
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Default Silly Question: Can an 8 Ohm Speaker on a 16 Ohm Output of a Tube Amp, Blow out the Main Fuse?

On Thu, 14 Jan 2021 23:06:08 -0700, Paul Dorman
wrote:

This is on an Ampeg VT-60 amp. Here is the schematic:


https://ampeg.com/support/files/Sche...SCHEMATICS.pdf


It was the main AC fuse F1, a 2.5 Amp Slow-Blow fuse, that was blown open.

Then I noticed the single 12" 8 Ohm speaker, was incorrectly hooked
up to the 16 Ohm output. Was this possibly the cause of the blown
fuse?

Some people on the internet, feel that with tube guitar amps, the
impedance of the speaker is not as critical as it is with solid-state
amps, and that the main danger is to have a no-load condition (an open).


Simple answer. No. If the fuse is blowing there is very likely a
fault. But there are fuses, and there are fuses. As important as the
current rating is the delay. Some are instantaneous - these tend to be
filled with sand to ensure fast heating of the wire. Then there are
varying degrees of delay - T , 2T etc. These fuses are used where
large momentary switch-on inrush currents are expected. Anything that
uses a mains transformer would qualify.

If you happen to switch on as the mains is moving through the zero
part of the cycle, you'll get a big magnetizing current that dies away
over a couple of cycles. You'll probably hear a "boing" from the
transformer as it does it too.

d