Screen grid muting

[KevinOConnor]

Hi Guys

Standby switches are inherently dangerous and widely misused. There is a Technical Article on my site about Standby switches which explains why they should not be used on most tube amps.

Muting the amp is a hazard as it allows one to "forget" that the amp is still powered. You leave it for a while and it is a fire hazard just as any other heat source can be in your home or jamming space. This is why certain countries in Europe will not allow amps to be sold unless the standby switch is disabled.

Standbys are needed if the tubes are very expensive, the power is very high, and/or when the voltages are very high. None of these parameters are met by any guitar amp ever made. The closest might be the SVT. Its standby was achieved by turning off the PT that supplied the plate and bias voltages while leaving powered the PT that supported the heaters.

To reduce output stage power, one can break the DC path to the OT feed, or break the DC path to the screen-stops. Doing either will cause a 'pop' so a small cap or very high resistance should be placed across the switch contact, or use an electronic interface to control the DC path. Breaking the cathode path to ground also puts the tube into a low or zero current mode and many companies used this method for both standby and power level control.

Assuming you still want the muting function, there are many methods that work. You can short any audio path to ground that does not have DC voltage on it, so many places in a preamp, at the power amp input, at the reverb mix point, etc. Linking the power tube grids will cancel signal but can upset the bias of the tubes and cause hum at the output.

Have fun

[wizard333]

I need to create total silence. I want to record the silence and then play it back at full volume while I sleep so it will cancel out the sound of the neighbor's barking dog. My question is do I need to make a stereo recording or will mono due? Sometimes there are two dogs.

I bought some blank tapes and put them in my stereo, turned it up all the way. My neighbor called the cops. He was a mime.

[SoulFetish]

Kevin, I would've replied with a quote but I'm on my phone and I don't want to deal with all that text.
if you capacitively couple the two grids together it's not going to upset the bias. But I concede it Isnt perfect system. If the output stage "perfectly" balanced, it would theoretically work better than many other methods.