Metropoulos Forum

Anyone using 18? I see some guys do...but with the voltage, I cant fiqure why.

It's the current.
With 3 preamp tubes:
and two EL34s = 3.9amps
and four EL34s = 6.9amps

Generally, 22awg is good up to 7amps.
That be said, marshall always used 22awg.

If you are using fat PT heater leads to the first socket then the 22awg between sockets is handling:
With 3 preamp tubes:
and two EL34s = 2.4amps
and four EL34s = 5.4amps

If you are worried about it, use 18awg on the power tubes, and 22awg to the preamp tubes

Even with the 18, your fuses should blow above 5 amps though correct?

There is no fuse dedicated to the heaters.

I suppose if there is an issue, it is that the insulation and of wire is going to start to burn up before the mains fuse would blow.

http://forum.metroamp.com/viewtopic.php?f=22&t=21482" onclick="window.open(this.href);return false;

There's some good info in here. I was wondering what the difference would be too,and if it would affect the feel of the amp due to voltage drop. It seems that the voltage drop would be negligible.

StuntDouble wrote:http://forum.metroamp.com/viewtopic.php?f=22&t=21482

There's some good info in here. I was wondering what the difference would be too,and if it would affect the feel of the amp due to voltage drop. It seems that the voltage drop would be negligible.

That last statment by Classic Tone makes a lot of sense. Check what your PT is running out and go with that I guess.

So....why is 18 guage used for wiring 4/12 cabs?

He is describing the wires connected to the heater winding.

You don't need heavy wire throughout. The current is heaviest nearest the transformer.
Here is the current the wires are carrying starting at v1:

Pre v1 = 0.3 amps
Pre v2 = 0.6 amps
Pre v3 = 0.9 amps
Pwr v4 = 2.4 amps
Pwr v5 = 3.9 amps
Pwr v6 = 5.4 amps
Pwr v7 = 6.9 amps (these are the wires going to the transformer)

As you can see the load accumulates as you move towards the transformer. As you move down the chain the wires are not only carry the current for the tube they are feeding, but also the current from the previous tubes in the chain.

22awg can handle 7amps. So really only the wires from the PT are even close to that.

So even after the first power tube its already dropping significantly. I guess for the power tubes it would be ok, but perhaps overkill to some respect.

In terms of speakers....they would be carrying a large amperage to warrent 18 awg?