ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

previous: Mike Re: Mesa-Tremoverb head -- 8/26/1998 8:07 AM

Re: Mesa-Tremoverb head (long)

8/26/1998 10:40 AM
GVB	Re: Mesa-Tremoverb head (long) Well it depends on how you look at it. It shouldn't over stress the tube, but it does wear the tube out. That is, if there are no design flaws in the standby circuit. The cathode in a tube is coated with materials that give off electrons when heated, and it will eventually be used up. When in standby, the electrons form a cloud around the cathode and most electrons will return to the cathode when switched off. Most, but not all. Their are mechanisms in place that will still wear out the coating when left in standby for long periods. When tubes are run in "non-standby", their is a bias current running through them, which uses up the coating faster. So it does shorten the useful life of a tube, but not as quickly as if used regularly. As for "flaws in the design, their are two that come to mind. Cathode stripping, the robbing of the coating material occurs when the heaters are not run at the proper voltage. Which is why variacs shorten the life of tubes when used to lower the voltage to an amp. If for some reason the voltage to the heaters changes in standby, it may also wear them out quicker. You can check by measuring the voltage on the heaters when in standby and regular operation. The other problem that can occur, is the destruction of filtering caps in the power supply. If the standby is located after a filter cap (it isn't usually), it can have a higher than normal voltage placed on it when no load is on the transformer. There is also the factor of thermal stress on components in the amp. The heat given off by the heaters can eventually cause nearby components to heat up and will eventually cause problems, if the amp design does not take this into consideration, or a component is faulty and "wear's out" faster than surrounding components. GVB

8/26/1998 10:40 AM

GVB

Re: Mesa-Tremoverb head (long)

Well it depends on how you look at it. It shouldn't over stress the tube, but it does wear the tube out. That is, if there are no design flaws in the standby circuit. The cathode in a tube is coated with materials that give off electrons when heated, and it will eventually be used up. When in standby, the electrons form a cloud around the cathode and most electrons will return to the cathode when switched off. Most, but not all. Their are mechanisms in place that will still wear out the coating when left in standby for long periods. When tubes are run in "non-standby", their is a bias current running through them, which uses up the coating faster. So it does shorten the useful life of a tube, but not as quickly as if used regularly.

As for "flaws in the design, their are two that come to mind. Cathode stripping, the robbing of the coating material occurs when the heaters are not run at the proper voltage. Which is why variacs shorten the life of tubes when used to lower the voltage to an amp. If for some reason the voltage to the heaters changes in standby, it may also wear them out quicker. You can check by measuring the voltage on the heaters when in standby and regular operation. The other problem that can occur, is the destruction of filtering caps in the power supply. If the standby is located after a filter cap (it isn't usually), it can have a higher than normal voltage placed on it when no load is on the transformer.

There is also the factor of thermal stress on components in the amp. The heat given off by the heaters can eventually cause nearby components to heat up and will eventually cause problems, if the amp design does not take this into consideration, or a component is faulty and "wear's out" faster than surrounding components.

GVB

Replies:

Steve A. GVB: ... -- 8/26/1998 7:28 PM