"Dave Plowman (News)" wrote in message
...
In article ,
Arny Krueger wrote:

"Dave Plowman (News)" wrote in message
...
I've been fixing a Cambridge A60 - turned out to be nothing more than
both speaker fuses blown. But thought I might as well check the
quiescent current while I'm at it. And the method given in the manual
is weird - replace the PS DC fuses with 15 ohm resistors and measure
the voltage across them.

Not having any high watt 15 ohm resistors to hand is there a different
way?


I don't know that those resistors have to have a lot of power rating.
If you are adjusting quiescent current, you're only talking a few dozen
milliamps. That doesn't drop a lot of voltage and therefore, the power
being dissipated is nominal.

They say to use 5 watt ones.


Not exactly high power in my book. My high power resistors are rated at
250-300 watts.

On Sun, 12 Jun 2011 07:11:48 -0400, "Arny Krueger"
wrote:


"Dave Plowman (News)" wrote in message
...
In article ,
Arny Krueger wrote:

"Dave Plowman (News)" wrote in message
...
I've been fixing a Cambridge A60 - turned out to be nothing more than
both speaker fuses blown. But thought I might as well check the
quiescent current while I'm at it. And the method given in the manual
is weird - replace the PS DC fuses with 15 ohm resistors and measure
the voltage across them.

Not having any high watt 15 ohm resistors to hand is there a different
way?


I don't know that those resistors have to have a lot of power rating.
If you are adjusting quiescent current, you're only talking a few dozen
milliamps. That doesn't drop a lot of voltage and therefore, the power
being dissipated is nominal.

They say to use 5 watt ones.


Not exactly high power in my book. My high power resistors are rated at
250-300 watts.


The 5 watt rationale is obvious. Still physically small and wire ended
yet big enough not to go pop if the current is a bit higher than
expected on firing up.

And of course if you are expecting a dissipation of about a milliwatt,
5W is an extremely high power resistor.

d

"Don Pearce" wrote in message
...
On Sun, 12 Jun 2011 07:11:48 -0400, "Arny Krueger"
wrote:


"Dave Plowman (News)" wrote in message
...
In article ,
Arny Krueger wrote:

"Dave Plowman (News)" wrote in message
...
I've been fixing a Cambridge A60 - turned out to be nothing more than
both speaker fuses blown. But thought I might as well check the
quiescent current while I'm at it. And the method given in the manual
is weird - replace the PS DC fuses with 15 ohm resistors and measure
the voltage across them.

Not having any high watt 15 ohm resistors to hand is there a
different
way?


I don't know that those resistors have to have a lot of power rating.
If you are adjusting quiescent current, you're only talking a few dozen
milliamps. That doesn't drop a lot of voltage and therefore, the power
being dissipated is nominal.

They say to use 5 watt ones.

Not exactly high power in my book. My high power resistors are rated at
250-300 watts.

The 5 watt rationale is obvious. Still physically small and wire ended
yet big enough not to go pop if the current is a bit higher than
expected on firing up.

I suspect that the 5 watt rationale is based on making the part finger-tip
safe. Or it makes for a durable part with heavy leads.

If someone makes a mistake with a bias pot, both they and the equipment are
probably better off with the low value part - it will act like a fuse.

And of course if you are expecting a dissipation of about a milliwatt,
5W is an extremely high power resistor.

If you do the math, you can easily see that 5 watts is vast overkill.