My VOX ADVT50 is not putting out any sound I don't know how to get sound to come out. It might be a short but I havent dropped it or anything. I have had it for 5 years but it has been out of commission for about 2 1/2 - 3 of those. I am looking to resell it or at least play on it.

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30 Jun, 2012

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The 'Valves' that are being referred to, are Vacuum tubes. They're in the pre-amp unit.

Electrolytic capacitors are used in the pre-amp, and maybe in the main amp.

[ Main amp uses digital circuitry, ( Transistors { Power MOSFET }, and Integrated Circuits { I.C. ), and not analog vacuum tubes ]

These are the weakest link.
To explain;

Basic construction of an Electrolytic Capacitor:

I'm willing to bet the type of Electrolytic capacitors used, are Radial Aluminum Electrolytic Capacitor's.

Radial meaning both leads, (Think short stiff wires), come out of one end.

The top example is an AXIAL design of electrolytic capacitor.
The bottom example is a RADIAL design of electrolytic capacitor.

The cylindrical blue part is a plastic sleeve. Under it is the cylindrical aluminum body, of the capacitor. Sleeve removed it resembles a 'Coca-Cola' aluminum can.

The body, or case, is just a cylindrical shaped 'can', open on both ends.

There is a round, flat, aluminum disk on the top, that seals the 'can'.
This has a shape etched into it part way. A lK or X.
It is called a Vent Cover.

The bottom of the 'can' is also sealed. It has a flat, round synthetic rubber disk. The leads of the capacitor poke through this disk.
It is the Bung.

Inside the 'can' are three strips.
One strip is thin aluminum foil. It is the Conducting Strip, and has the Positive ( + ) lead connected to it.

One strip is also a metal thin aluminum foil, but has a non-conducting medium applied to it.
It is the Non-Conducting Strip, and has the Negative ( - ) lead connected to it.

The last strip is usually a paper-like substance, and is soaked with Electrolytic Paste.

The paper-like strip is laid in-between the two metal strips, and all three are rolled up tightly. Then they are inserted into the 'can', with their two leads poking down through the Bung.
(That almost sounds WRONG! lol!)

When the capacitor starts to fail, (Go bad), the paste inside develops a gas. Hydrogen gas. The gas expands, and compromises the seals.
(Vent Cover and Bung)

The paste starts to ooze out from the pressure of the expanding gas.
(May crack the lK or X open in the Vent Cover, and/or push one side of the Bung, down, and out of the 'can')

So much paste loss, and the capacitor operates at a weakened state.
Too much paste loss, and the capacitor fails.

More than you wanted to know, huh?

When an electronic device, such as your amp, isn't plugged into electricity for some time, ( 2-1/2 to 3 years), the Electrolytic Capacitors used, go bad.
The chemical composition of the Electrolytic Paste breaks down.

It is for this reason, that I think some of the Electrolytic Capacitors are bad.

Visual signs of failure, using Electrolytic Capacitors on a desktop computer motherboard, as examples,

Scroll down. First page.

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