For a long time now, I switch on and off my amp without using the stand by switch.
And I realize that there’s not any problem with my tubes (my amp doesn’t have tube rectifier). Then I thought that there are a lot of amps out there, even commercial, without stand by switch.
I know that we are using it to warm up the cathodes and then apply safely the anode voltage. But safely for what? We are not exceeding any maximum rating.
Sorry if this is another newbie question and it’s just a routine for you to answer but I must ask if I’d like to learn.
And I realize that there’s not any problem with my tubes (my amp doesn’t have tube rectifier). Then I thought that there are a lot of amps out there, even commercial, without stand by switch.
I know that we are using it to warm up the cathodes and then apply safely the anode voltage. But safely for what? We are not exceeding any maximum rating.
Sorry if this is another newbie question and it’s just a routine for you to answer but I must ask if I’d like to learn.
Tom Bavis
It depends... on the amp design and how high the supply voltage is and whether it's fixed or cathode bias.
Problem is cathode stripping - the cathode doesn't heat evenly and whichever part reaches operating temp first will try to carry the full current... which overheats it resulting in loss of cathode coating, so no more electron emision in that spot. So it moves on down the cathode, which finally has no coating left - he's dead, Jim...
But it's not a problem with fixed bias, and it MAY not be a problem if the tube isn't run at the hairy edge of ratings (like some Fender amps).
It depends... on the amp design and how high the supply voltage is and whether it's fixed or cathode bias.
Problem is cathode stripping - the cathode doesn't heat evenly and whichever part reaches operating temp first will try to carry the full current... which overheats it resulting in loss of cathode coating, so no more electron emision in that spot. So it moves on down the cathode, which finally has no coating left - he's dead, Jim...
But it's not a problem with fixed bias, and it MAY not be a problem if the tube isn't run at the hairy edge of ratings (like some Fender amps).
I always have felt that cathode stripping is one of those phenomena looking for a home. it is a real thing, but doesn't really affect small circuits like guitar amps. It is something for the huge radio transmitter guys to worry about. After all, just how much current will be flowing through that 6L6 in your Twin when you flip it on? It isn't like you are cranking it and wailing at the time. And it takes only seconds for the tube to warm up enough that it no longer matters.
The main value of the standby switch in a guitar amp is that you can leave the amp warmed up and have instant-on when the break is over. And leavung the tubes hot all night reduces thermal stress over powering down every hour. Not to mention, there will be no noise surprises when you are across the room hitting on the waitress.
The main value of the standby switch in a guitar amp is that you can leave the amp warmed up and have instant-on when the break is over. And leavung the tubes hot all night reduces thermal stress over powering down every hour. Not to mention, there will be no noise surprises when you are across the room hitting on the waitress.
CATHODE STRIPTEASE...
Hi,
The only part in a tube that can possibly deliver whatever current is pulled is the CATHODE....
If that cathode has not reached it's operational temperature and more current is pulled than it can deliver at that point in time then cathode stripping will occur tearing oxides away from the cathode leaving a stripped area behind.
An area that is of no further use and if sufficient amounts of material are torn away the maximum amount of current that can be pulled will be reduced accordingly.
In practice all it takes is to wait sufficiently long for everything to reach operational temperature, that's all there's to it really.
Having a tube recifier will give a natural warm up sequence to all tubes downstream but it's not a must.
There's no evidence whatsoever, to my knowledge, that solid state rectification would in any way reduce tube life.
Standby switches are useful for guitar amps only to save some unnecessary power consumption. Other than that, the amp could be left idling just the same.
In fact I've seen more damage done by wrongly implemented standby switch sequencing to tubes then if there wouldn't have been such a switch at all.
The topic was discussed here before but I feel that the above should give you a general feel of what should never be done to any tube: draw more current than it can deliver.
Cheers,
Hi,
The only part in a tube that can possibly deliver whatever current is pulled is the CATHODE....
If that cathode has not reached it's operational temperature and more current is pulled than it can deliver at that point in time then cathode stripping will occur tearing oxides away from the cathode leaving a stripped area behind.
An area that is of no further use and if sufficient amounts of material are torn away the maximum amount of current that can be pulled will be reduced accordingly.
In practice all it takes is to wait sufficiently long for everything to reach operational temperature, that's all there's to it really.
Having a tube recifier will give a natural warm up sequence to all tubes downstream but it's not a must.
There's no evidence whatsoever, to my knowledge, that solid state rectification would in any way reduce tube life.
Standby switches are useful for guitar amps only to save some unnecessary power consumption. Other than that, the amp could be left idling just the same.
In fact I've seen more damage done by wrongly implemented standby switch sequencing to tubes then if there wouldn't have been such a switch at all.
The topic was discussed here before but I feel that the above should give you a general feel of what should never be done to any tube: draw more current than it can deliver.
Cheers,
JojoD818 said:
You can place a SPST switch in the line from the CT of the HV winding to chassis ground (or the B+ negative rail if this is not tied to the chassis) on the power xfmer supplying HVAC to the 5U4.
One thing to watch though is if you are running an electrolytic filter on the 5U4 cathode (cap input filter) you could harm the 5U4 with over current surge if this capacitor is too large in value.
If all you want is startup delay you could use a slow warm-up rectifier tube like a 5AR4 or a 5V4 instead of the 5U4. If yo want to use the 5U4 you can take the DC output from it and run it through a TV damper diode tube like a 6AX4, 6AU4 which is slow warmup but this will add more voltage drop to the B+.
You can also use a small tube like a 6AL5 with the two internal diodes wired in series with the coil of a small relay to close the center tap of the HV winding as explained first instead of a manual switch. When the 6AL5 warms up the relay will close.
I’m new over here so, sorry if I’m posting threads that have already been discussed.
As I understand, there’s no need of a stand by switch in normal amps.
Now I’m building a new P-P amp with 6L6GC at 420V / 50-60mA.
And I’m drilling holes, you know, sockets, xformers, SWITCHES….yes, over here I think about the stand by switch.
I’d like to cancel the main switch, too! I turn off my system from the main switch where all the power cables are plugged in. Or cancel this, too! And turn-off everything just with pulling out the cable from the wall socket!
I believe that switches became “old” with a lot of turn on and off.
But I’ll put a main switch, cause I already have done the hole.
One day I’d like my system without any switches and connectors. Only soldering joints. From the arm of my TT to speakers. And, power cables from the main socket to transformers.
Hi,
Not if you're careful not to send a signal full blast through the amp while it's still warming up anyway....which is where a mute switch_relay + timer controlled or not_ comes in handy.
Please don't.
It may cause nasty turn-on/turn off thumps through the speakers, resulting in damage to the voicecoil(s).
Best practice IME is to let the preamp and source(s) warm up with mute switch of the preamp engaged for a couple of minutes, turn on the amp(s) after that, then disengage the mute switch when all is fully operational.
To turn off the system, mute the preamp first, then switch off amp, sources and finally the preamp.
Cheers,
Not if you're careful not to send a signal full blast through the amp while it's still warming up anyway....which is where a mute switch_relay + timer controlled or not_ comes in handy.
Please don't.
It may cause nasty turn-on/turn off thumps through the speakers, resulting in damage to the voicecoil(s).
Best practice IME is to let the preamp and source(s) warm up with mute switch of the preamp engaged for a couple of minutes, turn on the amp(s) after that, then disengage the mute switch when all is fully operational.
To turn off the system, mute the preamp first, then switch off amp, sources and finally the preamp.
Cheers,
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