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Posted by: Scott Gentzen Jul 19 2008, 05:07 PM

This topic comes up on here occasionally. I finally got a cabinet to go with the Valve Jr I have so I decided to check it out.

I already had a 3' instrument cable and I just picked up a 3' speaker cable.

With the speaker cable, it sounds like it should.

The instrument cable is interesting. It is a lot different. The sound's muted, muffled, sorta. The low end is a little louder, but muddy and has a weird pulsating effect...kind of like a weird tremolo effect isolated to a certain frequency range. It increases as the volume increases.

I don't think it's damaging anything. It doesn't sound as "good" as one would expect it to sound but I don't think it's completely "wrong" either....just different. Makes me wonder what else I could put in between the head and the cab without wrecking the head..

Posted by: kjutte Jul 19 2008, 06:31 PM

DO NOT use signal cables. This is a power cable, it needs higher dimension wires, or it will litterally burn up.
I emphasize, do NOT use signal cables to cabinet.

The reason it sound muted is because your speaker needs alot more electrical current to function than a signalwire can deliver.

I don't know the exact digit, but a signal cable may be able to deliver 3amps or something, whilst a powercable can deliver 20amps.

Again; Do not use signal cables to cabinets!!!

Posted by: Andrew Cockburn Jul 19 2008, 06:38 PM

I totally agree - don't do it!

Worst case, the cable will fuse and break, then you will have no speaker connected to your amp and it in turn will then blow an output transformer or maybe redplate your tubes - either way ... D O N ' T D O I T !

Posted by: kjutte Jul 19 2008, 06:40 PM

Well, the fuses will blow, if the wires fuse together. May still damage the cab though.

Posted by: Bogdan Radovic Jul 19 2008, 06:47 PM

I hope Scott reads this topic as soon as possible !
I don't recommend experimenting with "what can you put in between speaker and head"

Posted by: kjutte Jul 19 2008, 06:49 PM

Yeah man. Though, it's quite obvious. The poweroutputs are red, and have lightninggrahpics next to 'em. Should ring a bell.

Posted by: Andrew Cockburn Jul 19 2008, 08:25 PM

Not necessarily , and definitely not if the wire melts and goes open circuit - that's when the real damage happens to a tube amp!

Posted by: kjutte Jul 19 2008, 09:00 PM

What's the fuse for then, if not overload, andrew? Melt together=short circut=massive overload.

If this is true A, our fuse cabinets at home would explode too, when the kid shoves something in the contact.

Posted by: Scott Gentzen Jul 19 2008, 09:39 PM

Actually, they don't. Not on mine anyway. There's the normal warnings about power and heat but nothing specifically on the head about cabling. I didn't really read the manual though.

Kept an eye on the cable for heat buildup and didn't play around like that for long. No damage done.

I'll not mess around with that anymore. I promise. Thanks for the heads-up, guys.

Posted by: kjutte Jul 19 2008, 09:41 PM

Hehe, well now you know. Signal and power is very very different cables.

Glad I could help!

Posted by: Andrew Cockburn Jul 19 2008, 11:06 PM

Because tubes have high voltages in them, not high currents. Fuses protect against high currents only. When you disconnect the speaker from a tube amp, the secondary of the output transformer goes open circuit, which reflects back through inductive coupling to the primary making it also go high impedance. Since the impedance is high, the voltage is also forced higher as there is nothing to load it down. If the voltage goes high enough, it can arc inside the transformer, burning out the insulation, or in some cases, the raised voltages within the tubes causes arcing there instead.

Either way, it isn't good, and a fuse won't protect you - but this is a peculiarity of tube amps only.

Posted by: kjutte Jul 19 2008, 11:15 PM

Even if the tubes have high voltage, the current will still raise massively when you short circut, and the fuse will instantly blow. Also, you say the voltage will raise, but I don't understand this

voltage=reistance*current, and when the wires melt, you get zero resistance, lower voltage.

Am I thinking wrong? Enlighten me please.

Posted by: Andrew Cockburn Jul 19 2008, 11:36 PM

I'm saying the wires melt and go open circuit, not fuse together ...

Posted by: kjutte Jul 19 2008, 11:47 PM

aha aha, I understand, and agree.

Btw, a question to you.
I have no cabinet for my tube amp, but I took the power tubes out.
can it still be damaged? It's been working nicely, and still am, butI keep reading that it's not good having it powered up without load.

Posted by: Caelumamittendum Jul 19 2008, 11:48 PM

On topic of this, I'm actually using one guitar jack cabel from my Boss GT6 output to my soundcards in, as well as one head-to-cab cable from my GT6 output to soundcard in. Is that bad in any way?

Never really put much thought into it, as they seemed pretty much the same. Had no other cables at the moment either.

Posted by: Andrew Cockburn Jul 19 2008, 11:51 PM

Hmm ... well, without power tubes, you wont have the problems mentioned above because there will be no voltage going directly across the OT, but you will almost certainly be getting higher voltage across the preamp ... that in itself may or may not be a problem depending on the amp. At the very least it will increase your clean headroom and mean you probably get less preamp distortion.Worst case you might blow the tubes and/or other components, but that is not very likely.

Posted by: kjutte Jul 19 2008, 11:52 PM

Head to cab cables are made for high current, and are not noiseless. Do not use these as signal cables.
I don't know what

Again, head to cab cables are power cables, and are ONLY ment for that purpose.



ohhhhhhhh andrew, so that's why my effects sound louder in clean channel than the others?

Please explain this further, I need to learn this stuff!

Posted by: Caelumamittendum Jul 19 2008, 11:56 PM

I'm getting a bit confused here. Which cables should I run from my GT6 to my soundcards ins? Just regular jacks?

Posted by: Andrew Cockburn Jul 19 2008, 11:56 PM

Not loader - cleaner ... distortion happens in tubes because they cant swing enough voltage to make a clean signal. If you increase the voltage they have to work with they can do louder clean work before distortion. For guitarists, we want that sweet tube distortion so this might make your amp distort less.

Posted by: kjutte Jul 19 2008, 11:58 PM

I see I see, and I think that's correct.
I also have a problem with my effectloop though.
All the effects seem to be more present in clean channel than the other ones. Why is that?
also I noticed that my "effect mix" pot meter is barely increasing the effect level.

Do you have any idea?

Posted by: Andrew Cockburn Jul 20 2008, 12:11 AM

Thats a little hard to say without knowing the design of them amp ... if you have atube buffered effects loop it could be affected by the higher voltage but I am really just guessing.

Posted by: kjutte Jul 20 2008, 12:21 AM

!!! of course, becuase it's standard signals, 4-20mA right?

So if my voltage raises, this signal becomes retarded.

Ok, I can't afford a cabinet at the moment- Can I just put a resistor at the output?
Well, of course I can, but do you have any suggestion to which?

Here is the diagram.

Posted by: Caelumamittendum Jul 20 2008, 12:23 AM

I'm just gonna quote myself in hope of a reply!

Posted by: kjutte Jul 20 2008, 12:24 AM

Yes, regular signal jacks.

Posted by: Caelumamittendum Jul 20 2008, 12:29 AM

Dumb question - though I got fairly good grades in physics - are those just the ones you'd have for your guitar to pedal/amp/head? I always just call them jack cables and not signal jacks! Sorry for being such a dumbhead.

Posted by: kjutte Jul 20 2008, 12:35 AM

You're not dumb. I build electro cabinets, that's why I know this stuff.
Anyway, yes, an ordinary jack.

You see, the power cables taht are from head to cab, have much thicker wires (becuase that means it can lead more electrones.) Imagine a waterpipe, a bigger one allows higher waterflow.

Same principle is here - You need more power to run the cabinet.
Ordinary jacks on the other hand, just carry signals, that are to be amplified later on.

Hope this helps!

Edit:
Powercables also don't have any noiseprotection, because high current=noise.
This is why you ALWAYS seperate signal from power, to avoid noise.

In my pedalboard, all my signaljacks are seperated from all power contacts etc, becuase it will be greatly noticed if I mess it together.

Edit again:
Jack btw, is just the plug. Both power and signal jacks, are jacks

Posted by: Caelumamittendum Jul 20 2008, 12:41 AM

Be quite you electro-geek!

Thanks for the answer - not sure I understand it all. Now I'll just go and play my guitar - that should be understandable to me.

Posted by: kjutte Jul 20 2008, 12:48 AM

Have fun buddy.

Btw andrew, incase you missed my post, I posted the diagrams for my amp further up.

Posted by: Scott Gentzen Jul 20 2008, 01:16 AM

14 gauge speaker cable, in my case.

Posted by: Andrew Cockburn Jul 20 2008, 03:17 AM

A resistor isn't the same as a speaker, a speaker is reactive as well as resistive, although it might be better than nothing. Though, as I said earlier, if you have no power tubes in there it should be ok ... any resistor you put in there would have to have a huge power rating though. Chances are if it hasn't blown up allready it probably won't.

the schematics make it look like you have a lot of solid state stuff in there as well though, which will run of a separate power supply, without spending several hours looking through the schematic I can't tell exactly what is going on here ... still not sure why your FX loop is louder on the clean channel ...

Posted by: kjutte Jul 20 2008, 08:46 AM

What do you mean by solidstate?

Yeah, I know that it has no reactans, but does it matter? I just have a transformer and an amplifying link, would it matter aslong as I have a load?

Posted by: Andrew Cockburn Jul 20 2008, 04:39 PM

Solidstate is transisters and such instead of tubes.

Really, to use a resistor for this it would need to be huge in terms of power dissipation - I really wouldn't go down that route ...

Posted by: Ivan Milenkovic Jul 20 2008, 05:58 PM

With a new tube amp that is a sensitive piece of equipment, I must say this is not too responsible of you mate. DOn't get me wrong, you could start a fire, damage the amp or maybe something even worse, god forbid.

Posted by: kjutte Jul 20 2008, 10:38 PM

Well, it has a tube preamp and poweramp.

Do you mean the controls of it? I am not an electronicsman, really.

Dissipation? do you mean to get rid of the heat? There shouldn't be any current there because signal goes out after preamp.