All tube amps, standby switch, and load

[Wasnex]

The point for me to use the standby switch is also to experiment sending the preamp of the Sadowsky sa200 into the power section of another amp to hear how the power section can make a difference.

The preamp in the SA200 should shut down in standby as well. So that's not going to work.

On the positive side, the Effects Loop is at the very end of the preamp; right before the Master volume.

To run your experiment, I suggest connecting a cab to the SA200. Insert a dummy plug into the Effects Return. This will lift the connection from the preamp. You can turn the Master volume down if there is any residual noise. Run the Effects Send to your other amp.

The effects loop runs at -4dBV (-1.79dBu). Probably not enough to drive a power amp to full power, but it may work in the Effects Loops of various amps.

 

[baxter_x]

The preamp in the SA200 should shut down in standby as well. So that's not going to work.

On the positive side, the Effects Loop is at the very end of the preamp; right before the Master volume.

To run your experiment, I suggest connecting a cab to the SA200. Insert a dummy plug into the Effects Return. This will lift the connection from the preamp. You can turn the Master volume down if there is any residual noise. Run the Effects Send to your other amp.

The effects loop runs at -4dBV (-1.79dBu). Probably not enough to drive a power amp to full power, but it may work in the Effects Loops of various amps.

Very interesting. Thanks!

 

[Passinwind]

Very interesting. Thanks!

A dummy plug with a shorting connection is preferable IME.

 

[byacey]

A signal may still be going to the output tubes on Standby, but the tubes would not be able to amplify that signal because the B+ voltage is missing from the plates. Standby typically eliminates the B+ voltage. This is typically a few hundred volts DC.



I always power my tube amps on with the amp in standby, for reasons of safety. I might power the amp off when not in Standby, and I might be sending a signal through the amp at that moment. Sometimes. But then I put the amp on Standby after it is powered off.

No B+, there is no signal present anywhere past the first preamp grid, in an all tube amp.

 

[byacey]

They were originally placed on old Fender guitar amps as a handy tool when servicing, but they are a great way to mute/ "Standby" your amp. Im sure Fender had that in mind too. After that, everyone just copied them, and after so long of seeing standby switches on amps, people freak out when they dont have one. All its doing it just cutting the signal being fed to the tubes. And no you cant harm your amp if you dont use the standby when powering on and off

Standby switch shuts off the B+ voltage. Without B+, the tubes will not pass any plate current, and cannot amplify any signal present on the grid.

 

[aiaosu]

Maybe this explains a bit better: The Great Standby Switch Myth | SweetwaterThe Great Standby Switch Myth | Sweetwater

This is an excellent article on the subject. I copied and pasted the same article when I saw this.

 

[Darrell Vachon]

It all makes sense with radios and lower power amps, but aren't SVTs up there with transmitter towers?

 

[K2000]

I don't know anything about transmitter towers, but Dennis Kager (who once serviced my SVT, and was for some years the head of the service department at Ampeg) told me to use the standby precisely because the SVT has high voltages. "Standby is good for soft-start" as someone in the amp tech's article states, and that is a worthwhile purpose, IMO. My amp is old, and wear & tear is a big concern, so I'll continue to use the soft start. Is this possibly unnecessary? I don't care, because it's not a big deal to start with the amp in standby for 10-20 seconds when starting it up, as was recommended to me.

The Sweetwater "myth" article said don't leave the amp in standby for more than a few minutes (yep) and that standby "soft start" is to protect the capacitors (not to protect the tubes). Okay, I stand corrected. Also note that recapping an amp is time consuming. Considering bench fees, recapping a tube amp is expensive - maybe even more expensive than replacing tubes (I don't know, I would have to dig up my last bill, and then try to make sense of the handwriting).

 

[baxter_x]

Standby switch shuts off the B+ voltage. Without B+, the tubes will not pass any plate current, and cannot amplify any signal present on the grid.

Is it the case with all standby or there are different designs?

 

[Wasnex]

I don't know anything about transmitter towers, but Dennis Kager (who once serviced my SVT, and was for some years the head of the service department at Ampeg) told me to use the standby precisely because the SVT has high voltages. "Standby is good for soft-start" as someone in the amp tech's article states, and that is a worthwhile purpose, IMO. My amp is old, and wear & tear is a big concern, so I'll continue to use the soft start. Is this possibly unnecessary? I don't care, because it's not a big deal to start with the amp in standby for 10-20 seconds when starting it up, as was recommended to me.

The Sweetwater "myth" article said don't leave the amp in standby for more than a few minutes (yep) and that standby "soft start" is to protect the capacitors (not to protect the tubes). Okay, I stand corrected. Also note that recapping an amp is time consuming. Considering bench fees, recapping a tube amp is expensive - maybe even more expensive than replacing tubes (I don't know, I would have to dig up my last bill, and then try to make sense of the handwriting).

I agree that starting the amp in standby may help protect some of the capacitors. Many SVTs run the plates very close to 700V. If none of the tubes are conducting, this voltage will probably rise to about 720V. Without tube current, Node B and C will also rise to 720V in a very short time. The stock capacitor for Node B was rated for 600V and the stock capacitor for Node C was rated for 450V. Node B feeds the preamp which also has a 450V capacitor. So that's 3 capacitors that could be stressed from starting the amp in operate rather than using the standby.

When the tubes are allowed to warm up. They start conducting as soon as the positive supply rails develop any voltage. The current passing through the resistors in the supply rails cause a voltage drop which keeps all of the nodes within a safe range.

I use the standby for turn on with every amp that has one.

One of my amps that lacks a standby is impacted by the over voltage problem. It's a 76 Matamp GT120 and it had all of the stock capacitors when I bought it in Europe, so apparently the problem was not too severe.

A few years in the US with occasional use and it needed a cap job. I believe that is because the power supply produces more voltage on 120V 60hz. The capacitors were being run overvoltage continuously, rather than just at startup. I used capacitors with a higher voltage rating and also increased the value of the resistor feeding the preamp from 10K to 16K. So far so good.

Of the top of my head, the other tube amps I own that lack a standy all use a tube rectifier. The tube rectifier has to warm up a bit before it will start producing voltage for the power supply.

 

[Old Garage-Bander]

I don't know anything about transmitter towers, but Dennis Kager (who once serviced my SVT, and was for some years the head of the service department at Ampeg) told me to use the standby precisely because the SVT has high voltages. "Standby is good for soft-start" as someone in the amp tech's article states, and that is a worthwhile purpose, IMO. My amp is old, and wear & tear is a big concern, so I'll continue to use the soft start. Is this possibly unnecessary? I don't care, because it's not a big deal to start with the amp in standby for 10-20 seconds when starting it up, as was recommended to me.

The Sweetwater "myth" article said don't leave the amp in standby for more than a few minutes (yep) and that standby "soft start" is to protect the capacitors (not to protect the tubes). Okay, I stand corrected. Also note that recapping an amp is time consuming. Considering bench fees, recapping a tube amp is expensive - maybe even more expensive than replacing tubes (I don't know, I would have to dig up my last bill, and then try to make sense of the handwriting).

All tube amps have "high voltage." Without defining what "high" means, it's just another way of saying, B+ or Plate Voltage.
Tubes in broadcast transmitters can have high voltage on the order of ten times what you might find in a tube amp. Measured in kilovolts, rather than volts.

 

[chadhargis]

I have only owned one all tube amp....My Ampeg PF-50T which is the gold standard for me tone wise. I love that thing.

I made sure to read the manual before I used it and the instructions on the Standby switch are right there in black and white. So I'll do as Ampeg suggests.


12. STANDBY SWITCH:
Use this switch to turn the Standby Power on or off. Press the top of the switch to disengage the Standby circuit [ON position]. The Standby mode allows the tubes to warm, or remain warm, without high voltage being applied to them, helping to extend tube life. This switch should be OFF when first turning the amplifier on. Allow the unit to warm up for at least 20 seconds before switching to the ON position. During short periods of non-use, the amp should be put into Standby mode.

 

[Old Garage-Bander]

I have only owned one all tube amp....My Ampeg PF-50T which is the gold standard for me tone wise. I love that thing.

I made sure to read the manual before I used it and the instructions on the Standby switch are right there in black and white. So I'll do as Ampeg suggests.


12. STANDBY SWITCH:
Use this switch to turn the Standby Power on or off. Press the top of the switch to disengage the Standby circuit [ON position]. The Standby mode allows the tubes to warm, or remain warm, without high voltage being applied to them, helping to extend tube life. This switch should be OFF when first turning the amplifier on. Allow the unit to warm up for at least 20 seconds before switching to the ON position. During short periods of non-use, the amp should be put into Standby mode.

Reading and following the instructions for a particular device is always the way to go.
If Ampeg say, do. Then do.

That does not necessarily mean this applies to other devices.
Gotta go by the instructions for those other devices then.

 

[chadhargis]

Reading and following the instructions for a particular device is always the way to go.
If Ampeg say, do. Then do.

That does not necessarily mean this applies to other devices.
Gotta go by the instructions for those other devices then.

Absolutely!