Speaker Wire Blues?

[bubba2]

After knowing very little about electronics and building an 18watt amp
by following the layouts and threads on this site, I have almost been elevated to amp guru god status by some local musos. You know the story, phone rings, so&so gave me your number saying you might know whats wrong with my 400watt fender blackface-quadmaster- rhythmlux combo... (like how the hell would I know.. I'll check my crystal ball).
Anyway a fellow dropped by with a 30watt Laney amp that was only putting out about ¼ power in volume. Handy I thought for a bedroom amp. Anyway checked all the tubes in my tube tester, all checked good. Tried new tubes in amp, still the problem remained.
Checked for dry solder joints, found none. Couldn’t see anything physically wrong with components, pcb board, wiring, inputs ect. Decided to check the 2x10â€

[stevesuk]

The great thing about tube amps is you can normally find a fault with one of the three free diagnostic tools.

Sight
Smell
Hearing

Just forget touch !!!

Just try that with a solid state microprocessor amp. Particularly, when there is just no sound

Also, they don't smell as good.

Steve UK

[stevesuk]

Thinking about your original post re: speaker wires.

I had a 20 watt head and G12M cab for repair and the 25uF 50V capacitor was blown wide apart. Also an EL84 valve was blown. It came back two weeks and many gigs later with another blown valve. I replaced them all with Marshall valves (cheap). Anyway to the point

I made up a lead out of twin cable and two jack plugs, and when the owner saw it he said ' can I have that ' when I said why, he said ' I have only got two guitar leads, and using one for the speaker means I only have one

So, I have read, a guitar lead has so much capacitance it damage a valve amp when used as a speaker cable.

Anybody know what it damages ??

Steve UK

[Ethan]

The capacitance of an instrument cable, even e cheap one, is pretty small. Especially if you put it in series with big inductors like output transformers and speaker coils. I can't imagine how that would do any serious damage to the output stage of a tube amp.
The conductors are small in instrument cables, so I suppose, if the current far exceeds the wire's limit, you could load the output stage, but even that seems unlikely.
What I'd be much more suspect of is an intermittent connection to the speaker (perhaps in the cable connector). A no-load situation could be fatal to an output tube, or even an output transformer.

Peace-
Ethan