Quote:
Originally Posted by ColinTheAmpMan1
Can I refer you to "Valve Amplifiers" by Morgan Jones, page 354
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And if you continue to read he goes on to discuss cathode poisoning which can occur when the cathode is heated to its normal working temperature with no HT voltage applied (which is exactly what happens in a guitar amp with a standby switch). He points out that this is not advisable and should be avoided.
You can indeed choose your information source as you see fit, equally important is how you interpret that information.
An internet search on the subject of cathode stripping will show that vast majority of informed opinion is that it is not a problem in receiving valves. Additionally I am not aware that any valve manufacturer has ever recommended that their receiving valves need to be pre heated in any way, they were (and still are) manufactured on the basis that they will likely be used in equipment where the HT and LT voltage are applied simultaneously from cold. There are a great many 70 and 80 year old valve radios still operating on their original valves that are surely testament to the fact that this is not a problem!
I have however seen many guitar amps with poorly implemented standby switches that have caused problems, switching high voltage DC is not trivial and the majority of the switches used for this in guitar amps are neither suitable nor rated for such applications. They typically use normal mains rated switches which are not rated for high voltage DC and over time arcing in the switch will cause failure. I have also seen amps with valve rectifiers (some from well-known manufacturers) where the standby switch has been placed between the rectifier and the reservoir capacitor, this is most definitely a bad idea as the current surge to charge the reservoir capacitor when it is switched on can cause arcing and failure of the rectifier valve.
The main reason guitarists like having a standby switch is that it is a convenient way to mute the amp during breaks without having to wait for it to warm up when you return. A much simpler and better way to do this is to fit a mute switch that grounds the signal path, no high voltage switching, no problems with cathode poisoning and as far as the end user is concerned it does exactly the same job. At best standby switches are unnecessary and in all probability they actually do more harm than good.