tube/resistor failure


I was just reading the Stereophile test of the Audio Research VS110 and they had an output tube arc/fail which also resulted in a burned out resistor. I have had output tubes fail in my amps (VAC and Cary) without any resistor damage. Have I just been lucky or is there something unique to the Audio Research designs that automatically results in resistor damage if a tube fails?
rhljazz
I just recently had the same tube/resistor failure problem in my Sonic Frontiers Power 2 amplifier. No big deal. open the bottom, replace the resistor, replace the tube.
I believe the reasoning is SONIC value.
Different designs. ARC doesn't have individual fuses on each tube, like some tube amps have, as they think it affects sonics. Also, it could be partially circuit topology, which can affect how the unit reacts to a voltage or current surge.
Tubes are just like any other electrical component i.e. they can fail in three different ways.

The first one is to short out i.e. act as a piece of wire rather than some type of component. This will typically cause an increase in current to flow, resulting in damage in support circuitry and components.

The second way is for the device to open up i.e. break the connection of the circuit. Since the circuit is not completed, current flow comes to a halt. While it is possible that other support components could be damaged when this happens, in most cases, the device will simply not function until the part is replaced and the circuit is closed, allowing current to flow.

The third way is for a device to alter its' electrical characteristics to a great degree. While all electronic components ( resistors, capacitors, transistors, tubes, etc... ) tend to "settle" due to use and thermal conditions, some parts can literally shift value way beyond circuit tolerance. These parts can shift up or down in value, so performance can be altered in several different ways. This can cause either erratic operation or no operation at all. In lesser cases, several parts may shift value, causing the product to perform in a less than optimum fashion, but still appear to be working normally. In many cases, this is what causes "production tolerance" from unit to unit and / or "lemons".

As such, there is no way to determine if one part failing will cause another part to fail. It is all up to the circuit design, how the part fails, the quality and ruggedness of the support components, etc...

As a side note, i would count your blessings and practice preventive maintenance. That is, if you have tubed gear, start checking your tubes every once in a while and keep a log. If you've got a circuit with four or eight identical tubes, obviously, you'll have to have some way to identify which tube goes where. This will help you to know when a tube is starting to "soften up" and allow you to keep the unit operating at peak performance without suffering any major catastrophes ( or at least reducing your chances ). There are always tubes that do fail for various reasons, but staying on top of the game can help reduce the casualties incurred. Sean
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Did Stereophile really say the tube will "always" cause the resistor failure? I don't see the automatic connection. You may not be lucky; more that Stereophile was unlucky.