How can I mute one side of the power tube pair?

[psychepool]

My recently built amplifier has a larger volume than expected, making it difficult to control it at home with only the master volume without attenuators.
While looking for attenuating methodes, I found a circuit like this.

a15.jpg

This is a power amplifier circuit diagram of Blackstar Artisan 15.
The vacuum tube is muted with a 2.2M resistance
I would like to apply this configuration to my amps. I'd like to ask you a few questions regarding it.

1.
Blackstar Artisan 15 is a cathode biased amplifier.
The amplifier I made has similar power amplifier with Marshall Plexi circuit, a fixtured bias amplifier.
Negative feedback is also applied.
It is a 40W amplifier that uses 6L6 pairs.
Is it possible to apply to the amplifier I've built in the same configuration as Artisan 15.

2.
If applicable,
How much spec should a switch use?
There's no space for a large switch on the panel that's like a power switch.
Since it's not a high voltage line, can I use a small toggle switch that used for effect pedals?

3.
There's Asymmetry value at the grid leak.(220K - 200K)
What's the reason?
Should I apply the same thing to my amplifier? (Marshal Flexi Power Amplifier)

4.
Will the life of the two vacuum tubes being used as pairs be no big difference, even if one side of the tube is used primarily as a mute?

5.
Does this method have enough attenuation?
It is not possible to predict how wide the attenuation will be through this switch because I haven't used Artisan 15.
I have applied penthod/triode switch on other amp, but the attenuation rate was not very satisfactory.


Please answer. Thank you.

[Stevem]

You can apply the blackstar deal , but it will have certain side effects with a 40 watt amp that you will need to deal with also, plus it will not sound good and the amp will still be too loud for home or bedroom use even running on just one output tube!

You need either a smaller ( 2 watt ) amp or get a at decent attenuator to place on the amps output, or if you have the room in the chassis install a power scallling kit from London power, this latter would be my pick!

[Phil_S]

We see questions like this more often than I'd have expected. "It's too loud. I want THIS AMP to be less loud." You can get an attenuator. It might affect tone in a way that you don't like, or maybe in a way you like.

The best solution to an amp that is too loud is to buy or build another amp. Many people don't realize that you need to go from 40W to 4W before you hear a meaningful difference in volume. Getting the 2W amp is the smart thing to do. Use the 2W or 1W amp at home. Use the 40W amp at a performance venue or practice space. That's just the way it is.

I've got a couple of low-watt amps. They really are very good for what they are. None of them sound like the 15-50 watt amps I've built. There is just something about the amount of air that a 50W amp will move that can't compare to 2W. Regrettably, I have nowhere to use those big amps. I don't play out. At some point I'll sell them.

[tubeswell]

What Phil_S said.

Except don’t just have big amps for playing out and little amps for practice at home, I say ‘why not have a range of little big and middle sized amps to reflect your mood?’

[thetragichero]

i have a switchable 22k high wattage resistor between the rectifier and first filter cap. knocks down the b+ enough to quiet down the amp considerably. i intended it as a standby switch but a lower power switch is nice

[pdf64]

Assume that’s got a cathode biased power amp?

[thetragichero]

yes sorry. that's important information!

[Phil_S]

Except don’t just have big amps for playing out and little amps for practice at home, I say ‘why not have a range of little big and middle sized amps to reflect your mood?’

Ah yes, that is why I keep them. I have the good fortune to live in a single family house on .33 Ac. If I turn it up, the neighbors might hear it, but I'm doubtful they'd complain. Now that we are empty nesters, I just need to wait until I'm home alone, which happens often enough. Pyschepool seem to imply he's got neighbor worries.

[psychepool]

Thank you for your many comments.

I already have a THD Hot Plate and am using it satisfactorily.
So if the blackstar method is inappropriate, I'll just use Hot Plate.
The reason why I'm interested in Blackstar's approach is that it seems to be a very simple work(without major changes in the amplifier structure) to deal with the amplifier itself without the use of attenuators and I wanted to apply it if there was a significant attenuation ratio.

Not long ago, I made a Dumble ODS with same power/output transformers and output tubes.
It has a large output but used it quite conveniently at home with only a master volume without attenuator.
Therefore, even though the output was similar to the amplifier that was made this time, it could be used at home and even in larger spaces.
But the new amplifier is a Bogner XTC based amplifier. For some reason, volume control is much more difficult on a lower volume setting than a Dumble.
So I thought it would be a good result for me if I could give a little help to the master volume control.

If there is no functional problem in applying this, I will apply it simply by wiring it and test it to see if it is necessary for me to make a final decision.

In short, the question is,
Is there is no particular problem applying Black Star's approach to the Marshall Plexi Power Amplifier?
Why is the value of grid leak resistors asymmetric? Can't it matter if you put 220K on both sides?

[Tony Bones]

The Blackstar is cathode biased, so the resistors around the switch are connected to ground. It should work with fixed bias where the resistors are connected to the bias supply.

I don't think it's important to use different size resistors (200k & 220k.) The big resistor (2.2M) is to reduce noise when using the switch, so I would keep it.

[pdf64]

That arrangement probably works fine with the blackstar because it operates close to class A, so won’t sound crap if one p-p side isn’t doing anything. That may be a different matter with a fixed bias amp that can’t operate anywhere near class A.
But as you’re interested, give it a go!

[printer2]

I have used a switch to disconnect the signal to one side of the P-P pair. It was a cathode biased amp but with fixed bias it should work. If the switch come after the PI coupling capacitor the normal bias will still be on the grid of the amp. That tube will idle along while the other will follow the signal it is given. The asymmetrical clipping will not sound like the amp normally overdriving but more like a single tube amp. The reduction in loudness is not a great amount but it is noticeable. The switch can be a simple mini-toggle switch, not a lot of current or voltage. Besides, if you switch it when not playing through the amp it will see no stress at all. The easiest thing to do is temporally disconnect one side of the coupling cap and play through the amp, then use an alligator clip and reconnect the cap to hear the difference.

[Guy77]

Here is another very cool way to get the effect of disconnecting one power tube in a push pull amp.

https://el34world.com/Forum/index.php?topic=4401.0

It works with cathode biased amps and was used by Carr amps on there Viceroy model back in the day.
(To use this with fixed biased biased amps you would need to add the feature that switches them from fixed to cathode biased first)

This method involves having a separate cathode resistor for each power tube and then you disconect one of the bypass caps, on one or on both of the power tubes cathode resistor. If you read to the end of the post you will see how they successfully placed this on an on - off- on switch dpdt and giving you 3 different power levels.



There are some youtube videos of the Carr Viceroy/Vincent and they demonstrated this feature .

Cheers

Guy

[psychepool]

Looking back at the circuit with a cold heart,
In conclusion, seems to be the same result as leaving only one side of the pot zero in the La/Mar PPIMV.
Rather, I think Lar/Mar PPIMV would be more effective.
PPIMV has a disadvantage of limiting power tube overdrive, but it is not an amplifier for that purpose anyway.
I think it would be satisfying to be able to use more phase inverters in plexi mode.