# Re: Almost had a Marshall Heart Attack

• From: Jim <inse@ttle>
• Date: Thu, 30 Sep 2010 14:37:45 -0700

On 9/30/2010 1:59 PM, RichL wrote:
<salty@xxxxxxx> wrote in message
news:jtq9a6t6d58vmrqcuvrqqlvulj5avdp83b@xxxxxxxxxx
On Thu, 30 Sep 2010 15:02:00 -0400, "RichL" <rpleavitt@xxxxxxxxx>
wrote:

"Jim" <inse@ttle> wrote in message
news:MOednRmyzIAfRTnRnZ2dnUVZ_qednZ2d@xxxxxxxxxxxxxxxxxxxxx
On 9/30/2010 9:47 AM, salty@xxxxxxx wrote:
On Thu, 30 Sep 2010 09:37:29 -0700, Jim<inse@ttle> wrote:

On 9/29/2010 7:26 PM, WB wrote:
On 9/29/2010 5:36 PM, jtees4 wrote:
their prices seem good to me and
you can buy small or large quantities.
http://www.digikey.com/

Oh yeah. Digikey use to only sell parts in large quantities,
but started to allow smaller orders. I've gotten discrete
(IC) from them before. www.partsexpress is a fav too.

Auto parts stores tend to have a large section of fuses
too.

6.3 amps ... that baby sure sucks the electrons.

But it's on the filament source.

A typical hand-held hair blowdryer draws more than twice that, and if
the fuse is rated at 6.3 amps at 120 volts, the amplifier draws less
than that in normal continuous operation with all settings cranked to
max

I pointed out that it's the filament supply because of the low voltage.

If you consider POWER available at the fuse rating:

6.3A @ 6.3V < 40W

Bad math. You've gotta transform the current along with the voltage
(they
scale inversely) so the below calculation is the right one:

6.3A @ 120V would be > 750W

On the secondary side, the voltage is 6.3 V so the current would be (120
V/6.3 V) x 6.3 A = 120 A!

Where did you come up with that crazy formula?

As far as I know,

6.3 Amps at 6.3 volts = about 40 watts.

That's correct but inappropriately applied in this situation.

The point is that the 6.3 A fuse is on the primary side of the
transformer, where the voltage is 120 V.

But it's not.

The amp uses a 6.3A filament fuse and a 3.15A mains fuse.

On the secondary side of the transformer, the voltage is stepped down to
6.3 V but the current is stepped up to 120 A.

The power has to be calculated with values of voltage and current on the
*same* side of the transformer. If you do this, you get 756 W,
regardless of whether you use the voltage and current values from the
primary side or the secondary side.

.

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