Mute switch

[demonstratedspatulas]

As we all know, there is really no need for a standby switch.

So instead, I would rather just include a mute switch on my amp.



I'm guessing this is the best way to do it, unless anyone knows a better way.

C6 is the input to the PI.

Would like to avoid any popping sound if possible.

[Roe]

just turn down the volume instead

[demonstratedspatulas]

Volume has been set to match the band, it's annoying to pick that level out again. A mute switch is very nice to have.

[Stevem]

The fact is that any tube idling in class A like signal gain stage tubes do will live a lot longer if the DC voltage is removed by means of a standby switch when not playing thru the amp!

If you want to put in a mute switch in install one in your guitar if it's not active such that it shorts out the signal just like the switching input jacks do in our amps.

[sluckey]

Another option... Look at the Silvertone 1484. I don't remember any switch pops.

https://el34world.com/charts/Schematics ... ne1484.pdf

[wpaulvogel]

I’d experiment with a resistor across the contacts between 10-22Meg to eliminate popping.

[sluckey]

I’d experiment with a resistor across the contacts between 10-22Meg to eliminate popping.

The pot is already across the switch contacts.

[R.G.]

The fact is that any tube idling in class A like signal gain stage tubes do will live a lot longer if the DC voltage is removed by means of a standby switch when not playing thru the amp!

Academic note: this would be true if life was simply in terms of power-on-hours; but it's not that simple. It is true that hours of electron emission and hours of active cathode bombardment do add up to poison cathode emission, and hours at temperature do erode and eventually open heater filaments. But for something like a 12AX7 left on continuously, this may be a huge number of hours, the equivalent of decades of continuous operation. For power tubes, the thermodynamics are worse, but the number of hours of life when idling at current may still be many years altogether. One other big factor in lowering life is the number of thermal cycles and current surge cycles.

Each turn on/off cycle involves cycling the heaters from dead cold to hot and back again. This stresses the heaters both mechanically and thermally as they heat up. Current surges cumulatively age the cathode oxide coating far more than idling. And worse yet, some Marshall models (in)famously switch off the power tube bias with the standby switch as well, so there is a pulse of instant underbias and high current every time it's being switched out of standby.

These factors weigh in for having to make a decision about switching off DC versus muting. It's not simple. For short periods, mute is better for more life. For longer periods, removing DC becomes better for longer life. For even very long periods, power off is better. The difficult thing is to define exactly how much time "short", "longer" and "longest" really are. This probably depends on the power supply voltages, bias currents and even the thermal situations inside the amp enclosure.

End Academic Note.

[Stevem]

Yes, I forgot and you reminded me!

I have a 1484 and it's a very quiet way to mute the amp.

[pompeiisneaks]

Interesting, I guess if the PI is imbalanced enough some sound might come through, but mostly it just cancels each side out with the other. Smart!

~Phil

[demonstratedspatulas]

My understanding is that the main cause of tube decay is cathode material evaporation, which is entirely determined by the cathode temperature, switching the DC off won't help.

[demonstratedspatulas]

If you want to put in a mute switch in install one in your guitar if it's not active such that it shorts out the signal just like the switching input jacks do in our amps.

What if someone else needs to use my amp? (Which happens time to time!) I would prefer something more universal also this forum is about building amps, not guitars, is it not?

[pdf64]

The fact is that any tube idling in class A like signal gain stage tubes do will live a lot longer if the DC voltage is removed by means of a standby switch when not playing thru the amp...

That may seem intuitively obvious but I don’t think it’s correct.
As the total cessation of HT current whilst heaters remain fully energised may lead to cathode poisoning / interface resistance / sleeping sickness, see Tomer p33 http://tubebooks.org/Books/Atwood/Tomer ... 0Tubes.pdf
Hence Jahn’s and Merlin’s standby with trickle bypass.
https://el34world.com/charts/Schematics ... _400ps.pdf
http://www.valvewizard.co.uk/standby.html

It may be that the final generation of audio tubes that were adopted for our application are not prone to developing interface resistance, ie the special cathodes of premium tubes mentioned by Tomer became the norm. But then why would a ‘proper’ highly competent tube EE such as Ed Jahn bother with the trickle bypass in his pet project, the 400PS?
Hence it seems reasonable to draw the assumption from that if he thought it worth doing something to mitigate that issue arising with HT standby, then it is a real thing.

[martin manning]

Anybody know what the "special design" in the 010309 tube is?

[Kagliostro]

Just to mention it

This is an unusual but effective way for a standby

note, a relays disconnect the CT of the B+ and G2 supply windings and an SPST connects G2 to the negative voltage

http://www.chambonino.com/construct/constwire1.html



Franco