Bare Knuckle Pickups Forum
Forum Ringside => Tech => Topic started by: MrBump on May 18, 2011, 02:47:28 PM
-
Guys, when powering down a valve amp, do you just power off immediately, or switch to standby first, wait, then power off?
I'm not sure I can see a good reason NOT to power off immediately... but I've read some people swear by waiting.
Mark.
-
power off immediately here.
leaving your amp on with no HT voltage for long periods is bad, using standby at turn-on to wait for the valves to warm up is one thing, but your not 'cooling' the valves down by using standby at switch off. may as well just switch it off.
there is also an argument for having no standby switch at all in modern amps.
EDIT: here is the wisdom from Merlin himself http://www.freewebs.com/valvewizard1/standby.html
I've read this a few times but always forget the reason for needing a standby at turn-on, and why amps have them.
-
I use my standby to turn the amp off, but its just to the amp doesn't pop through the PA.
-
power off immediately here.
leaving your amp on with no HT voltage for long periods is bad, using standby at turn-on to wait for the valves to warm up is one thing, but your not 'cooling' the valves down by using standby at switch off. may as well just switch it off.
there is also an argument for having no standby switch at all in modern amps.
EDIT: here is the wisdom from Merlin himself http://www.freewebs.com/valvewizard1/standby.html
I've read this a few times but always forget the reason for needing a standby at turn-on, and why amps have them.
Huh, I always thought it was the cathode stripping reason. Mr. Blencowe is the man so knowledge gained. Thanks for that.
-
i use my standby for turning off so it's in the right position for the next time i turn it on.
-
Further to this discussion, I leave my amp ON 'warming up' while we're setting up for a gig (i.e. not on standby) - I just mute it via my tuner pedal.
This has the added bonus of getting some hiss through your speakers and warming up the voice coils a little - nothing worse for your speakers than going from cold straight to blasting out the power chords. I got this tip from one of the design engineers at Celestion to help prolong the life of speakers.
Lastly, if anything is gonna go wrong with the amp, you'll find it generally will with the amp sitting there in 'play' mode. When it's in standby, you always have the chance something might give it up when you flick the switch. At least if something goes wrong earlier in the night, you have time to sort something out.
-
Excellent information here - I love to see all the old mythology being debunked.
-
Further to this discussion, I leave my amp ON 'warming up' while we're setting up for a gig (i.e. not on standby) - I just mute it via my tuner pedal.
This has the added bonus of getting some hiss through your speakers and warming up the voice coils a little - nothing worse for your speakers than going from cold straight to blasting out the power chords. I got this tip from one of the design engineers at Celestion to help prolong the life of speakers.
Lastly, if anything is gonna go wrong with the amp, you'll find it generally will with the amp sitting there in 'play' mode. When it's in standby, you always have the chance something might give it up when you flick the switch. At least if something goes wrong earlier in the night, you have time to sort something out.
Nice tip
-
^+1, will have to remember that
-
true experience. one of my tubes started redplating the moment i flicked the ON switch. standby only sends power to the heaters. there's no cool down phase when standby. I put it in standby 'till the hiss stops and turn it off. to avoid pops
good tip about the speakers hth! will surely apply that from now on. thanks!
-
On most amps a standby switch is unnecessary.
When valves ruled the world no other electronic devices using receiving valves (TVs, wireless sets etc), had standby switches.
Fender started to use standby switches in the late 50s. In my view this was to a) protect the filter caps from over voltage, and b) prevent arcing in DC coupled cathode followers - the standby switch very quickly appeared after the first Fender models with a DC coupled CF appeared in 1956.
Cathode stripping simply doesn't happen at the voltages found in valve amps.
As most other manufacturers followed Fender's lead standby switches are now seen as a standard feature (and I think you would trouble selling an amp without one).
Perversely, adding a standby switch has, in my view, caused reliability issues in some amps, eg the VOX AC30CC. The original AC30s did not have a standby switch, and as they have a valve rectifier the HT came up slowly as the rectifier warmed up limiting in rush current.
In the AC30 CC using the standby switch before energising the HT lets the filament of the valve rectifier warm up so that the rectifier experiences significant in rush current, which can and does cause the rectifier to short out.
I've seen several AC30CC with shorted rectifiers, and whilst I suspect that modern rectifier valves aren't that robust, this is a fault I rarely see in 60's AC30s and Selmers which use a valve rec with no standby switch.
-
In my view this was to ... prevent arcing in DC coupled cathode followers - the standby switch very quickly appeared after the first Fender models with a DC coupled CF appeared in 1956.
That's an interesting point. Presumably Leo didn't figure out DC elevated heater supplies.
Valve rectifiers certainly give the other tubes a nice soft start, certainly compared to just throwing the standby switch on a SS rectifier and letting the full HT loose on a hot tube. Makes me wonder if anyone's ever built a solid state power supply that mimics this, slowly ramping up the voltage?
-
In my view this was to ... prevent arcing in DC coupled cathode followers - the standby switch very quickly appeared after the first Fender models with a DC coupled CF appeared in 1956.
That's an interesting point. Presumably Leo didn't figure out DC elevated heater supplies.
Valve rectifiers certainly give the other tubes a nice soft start, certainly compared to just throwing the standby switch on a SS rectifier and letting the full HT loose on a hot tube. Makes me wonder if anyone's ever built a solid state power supply that mimics this, slowly ramping up the voltage?
Lots of P.A. power amps have a slow ramp up to full voltage. Can't see why you couldn't do that in a guitar amp. I'd actually prefer it to a standby. I usually flip the power, get all the things in order(guitar on, cable in, find a pick) and then flip the standby which isn't enough time for things to get fully hot anyways...
-
just out of interest, how does a DC elevated filament supply help reduce (protect against) arcing in a cathode follower?
I thought the arcing was caused by the cathode being at ground potential for a split second when the CF grid get the blast of HT, and the arc is from grid to cathode. I thought the protection against it is to add a resistor and diode in series between the grid and the cathode of the follower. I didn't know different filament supplies made a difference.
-
My Orange doesn't have a standby switch. It's got 4 EL34s, and when you power it on it's like some arcane electric chair or something - you hear this "THUMMMM!!!" as the power hits its internal organs...
Kinda scary...
My Egnater is far less scary. Although I guess that's all an illusion...
-
just out of interest, how does a DC elevated filament supply help reduce (protect against) arcing in a cathode follower?
I thought the arcing was caused by the cathode being at ground potential for a split second when the CF grid get the blast of HT, and the arc is from grid to cathode. I thought the protection against it is to add a resistor and diode in series between the grid and the cathode of the follower. I didn't know different filament supplies made a difference.
you're reducing the heater-cathode voltage (180v design max) to within its safe limits - most amps with a cathode follower are pushing the design spec limits here, but the majority of ECC83s/12AX7s cope with it.
I use DC elevated heaters on everything now, its simple, gets rid of any hum and makes the amp more reliable - whats not to like.
-
just out of interest, how does a DC elevated filament supply help reduce (protect against) arcing in a cathode follower?
I thought the arcing was caused by the cathode being at ground potential for a split second when the CF grid get the blast of HT, and the arc is from grid to cathode. I thought the protection against it is to add a resistor and diode in series between the grid and the cathode of the follower. I didn't know different filament supplies made a difference.
you're reducing the heater-cathode voltage (180v design max) to within its safe limits - most amps with a cathode follower are pushing the design spec limits here, but the majority of ECC83s/12AX7s cope with it.
I use DC elevated heaters on everything now, its simple, gets rid of any hum and makes the amp more reliable - whats not to like.
Absolutely.
If the cathodes are cold, neither the CF nor the preceeding valve stage will conduct current.
Thus if you turn the HT on then there will be no voltage drop across the plate load of the triode preceeding the CF ie the full B+ will be imposed in the CF grid, and this can cause arcing. Merlin Blencowe's arc protection circuit prevents this.