by (soundmasterg) » Wed Jan 28, 2015 2:00 am
Amps that use receiving tubes, which would be all musical instrument amps, do not need a standby switch. There are a couple special cases such as the Fender 400 PS mentioned earlier, and an Ampeg SVT can use one too though it is not strictly necessary. People usually want to recommend a standby switch so that you don't have the problem of cathode stripping. With receiving tubes and the voltages used on them, cathode stripping is not an issue. It says something to that effect in the RCA tube manual, and I believe also in the Radiotron Designer's Handbook (RDH4). If something is using transmitting tubes at the voltages those often run at, say upwards of 700 volts, then cathode stripping can become an issue and standby is helpful or in some cases necessary for the tube life.
Now don't get me wrong..... a standby switch can be useful, especially in a live environment in between sets to mute the sound. The typical way to do this in the circuit is to interrupt the B+ high voltage supply to the tubes but there are other ways to do it that are less brute force and work equally well. The B+ interrupt method does have advantages from the repair standpoint as it is handy to be able to shut of the high voltage at times for the repairman. Many vintage amps such as the 5E3 Tweed Fender Deluxe never had a standby switch and the tubes in those last a loooong time. Amps with a GZ34/5AR4 rectifier tube will have a slow warm up time anyway as that tube has that built into it's function, so amps that use that rectifier tube have even less reason to use standby except for the muting feature.
Turning amps on and off when you use them is not good for the tubes and will make them wear quicker, especially rectifier tubes, which are already spotty on reliability these days. If you do a sound check and then will be not playing for 3 hours or something, then it is best to shut the amp off, and turn it on again a bit before the show so the tubes will warm up. If you do a blues jam or something and you put it on standby in between sets then that is a good use of a standby circuit and protects the tubes and their life much better than turning it off between sets.
Most musicians expect that an amp should have a standby switch and think of it as being a cheaper amp if it does not. This is mostly due to conditioning and internet scuttlebutt since most people, especially in the US, grow up with Fender amps that usually have a standby switch.
Greg
