It does pop up in some other things. My 70s Dynacord Eminent II has pretty much no Fender influence to the design yet uses a standby switch. I reckon they did it because they used 450v rated filter caps on a 420v rail, where starting it up from cold would likely exceed the cap rating.
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Tube Amp Without Standby
- Thread starter Eternal Day
- Start date
It does pop up in some other things. My 70s Dynacord Eminent II has pretty much no Fender influence to the design yet uses a standby switch. I reckon they did it because they used 450v rated filter caps on a 420v rail, where starting it up from cold would likely exceed the cap rating.
The cathode stripping not the big deal at typical guitar amp voltages...not dealing with transmitters here.. is not really about the valves..
However, if you did not have a stand-by switch and your amp uses solid state rectification.... You would apply high voltage across every component in the amp including pre-amp stages...until the all tubes warmed up and draw enough current to pull down the voltages .... Typical Marshall that idles at 465V would see roughly 500V un-loaed across all components until tubes warm-up.. figure 6 to 8 seconds warm-up time.... The pre-amp filter caps and coupling caps may be rated at 400V during this 500V over-stress...sometimes not an issue, but if the amp is old..
If all your components are up to the task of high voltage over-stress for 8 seconds each time you turn your amp on..then I guess your all good..
There are cases such as with FOLLOWERS and CASCODE topology, where you can get a HEATER-to-CATHODE breakdown before the valves are warmed up....due to the higher voltage occurring at the cathode when the tube is cold.. Proper design can prevent this...but there are amps out there that have this issue.. Also need to be careful when the heater is floating on the DC voltage....
I like the STAND-BY switch....so I can switch out guitars quickly between songs without having to shut down the amp...I sort of treat it as a MUTE switch..
However, if you did not have a stand-by switch and your amp uses solid state rectification.... You would apply high voltage across every component in the amp including pre-amp stages...until the all tubes warmed up and draw enough current to pull down the voltages .... Typical Marshall that idles at 465V would see roughly 500V un-loaed across all components until tubes warm-up.. figure 6 to 8 seconds warm-up time.... The pre-amp filter caps and coupling caps may be rated at 400V during this 500V over-stress...sometimes not an issue, but if the amp is old..
If all your components are up to the task of high voltage over-stress for 8 seconds each time you turn your amp on..then I guess your all good..
There are cases such as with FOLLOWERS and CASCODE topology, where you can get a HEATER-to-CATHODE breakdown before the valves are warmed up....due to the higher voltage occurring at the cathode when the tube is cold.. Proper design can prevent this...but there are amps out there that have this issue.. Also need to be careful when the heater is floating on the DC voltage....
I like the STAND-BY switch....so I can switch out guitars quickly between songs without having to shut down the amp...I sort of treat it as a MUTE switch..
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Mainly the Standby - Switch is an "my amp has one more switch than yours" - Switch.
There are lots of tube amps that are constructed without a Standby - Switch which are either "On" for years or turned on/of by plugin / unplugin the power plug. I am talking about the amplifiers of vintage music boxes.
There are lots of tube amps that are constructed without a Standby - Switch which are either "On" for years or turned on/of by plugin / unplugin the power plug. I am talking about the amplifiers of vintage music boxes.
Since this is a BASS forum.... I will provide you with a classic case off where you DO need a STAND-BY switch for a bass amp..
The first series of AMPEG SVT heads used 6146B tubes...
This tube has a 250V limitation on the screens...
If you fire the amp ON with the STAND-BY switch the screen on the output tubes will see over 700V for around 8 seconds until the voltages come down to where they should be...
In the meantime you could hear arcing on your 6146B tubes... I have seen this first hand on customers who re-fuse to believe...
The first series of AMPEG SVT heads used 6146B tubes...
This tube has a 250V limitation on the screens...
If you fire the amp ON with the STAND-BY switch the screen on the output tubes will see over 700V for around 8 seconds until the voltages come down to where they should be...
In the meantime you could hear arcing on your 6146B tubes... I have seen this first hand on customers who re-fuse to believe...
No that won't hurt your amp at all, many low power tube amps came with no standby and it doesn't matter where the volume is set either because your amp puts out nothing until the tubes are warmed up enough to work (15-30 seconds). You need the standby on big amps like SVT's, Sunns etc to protect the power tubes, they don't like plate voltage without the filiments warmed up, your tubes will last longer if you use a standby switch if it is there it is there for a reason and not to protect speakers, to protect power tubes.
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Any amp that has a standby switch, should be left in the standby position until the power tubes have warmed up enough to conduct (at least 15-20 seconds, 30 is better), especially an SVT even if it has 6550's in it. I use it on Fenders, SVT's, B-15's etc
