Tweed Twin power reduction

[Randall]

I have a neurotic, PITA customer who owns a High Power Tweed Twin 2x12. It is loud, and he is always fussing about how to make it less loud. He heard that two of the 6L6s can be removed, so we did that, but it's still too loud. He heard that one of the speakers could be disconnected, but as I understand it, half the power, half the impedence, but removeing a speaker doubles the impedance, so I told him no. Now he wants to get an attenuator, which I am not in favor of here, but it is his amp to blow up. I am sure he is going to ask if he can run it on two tubes, and although my gut says that is not a good idea, I am not sure.

Enlighten me?

[Leo_Gnardo]

He heard that two of the 6L6s can be removed, so we did that, but it's still too loud. He heard that one of the speakers could be disconnected, but as I understand it, half the power, half the impedence, but removeing a speaker doubles the impedance, so I told him no.

Other way 'round. Run it on one pair of 6L6, one speaker, that should be OK. Except ... it will likely still be "too loud." So, there are speaker attenuators you want to avoid... Triode wiring for the output section which might help. Or selecting speakers that aren't as efficient & bright as the ones in there. Expensive experiment, yes. Let me point out Tone Tubby's "San Rafael Specials" which have a relatively low efficiency (94 dB/W/M IIRC) and very mellow high frequency response. Some guitarists around here have found joy using them with "untameable" super bright amps. I haven't found anything else quite like them.

[nevetslab]

I have a neurotic, PITA customer who owns a High Power Tweed Twin 2x12. It is loud, and he is always fussing about how to make it less loud. He heard that two of the 6L6s can be removed, so we did that, but it's still too loud. He heard that one of the speakers could be disconnected, but as I understand it, half the power, half the impedence, but removeing a speaker doubles the impedance, so I told him no. Now he wants to get an attenuator, which I am not in favor of here, but it is his amp to blow up. I am sure he is going to ask if he can run it on two tubes, and although my gut says that is not a good idea, I am not sure.

Enlighten me?

While there are numerous amps that change power level by going from pentode to triode mode, or dropping the power supply potentials in half, those to me haven't changed the SPL level of the amp, though probably do limit the max spl from those power reduction techniques. While working on one of the Blackstar Series One guitar amps, it has a control called Dynamic Power Reduction, which will drop it's max output from 100W down to 10W, by both reducing the power supply voltage on the power tubes (no doubt at the CT of the OT Primary), AND also reducing the grid drive to those tubes, without changing the bias level or output impedance. That's the first control I've heard that actually DOES what their claims state. The SPL level at the min setting is substantially lower than at the Max setting, and sounds really good! I don't have any of the circuitry in my database on that, and implementing that on your customer's amp would be way beyond the cost/enginering to make it happen. Mesa shows their tricks for going between Triode & Pentode operation, Fender shows theirs for cutting the power supply voltages in half, and those aren't extremely challenging, but..........no doubt more than your customer would want to pay.

[glebert]

I have a neurotic, PITA customer...

Enlighten me?

Fire your customer

[nickb]

Lower the voltage to the screens and adjust bias to compensate will allow you to get just about any power out you want. I could give more detailed info but I'd need the schematic as I'm not sure which model we are talking about here.

[Pedro Vecino]

Is it a 5F8A? In the Bassman 5F6A a conventional master volume after the treble control works very well. A suitable place is on one of the inputs of the normal channel.

[alexradium]

I have a neurotic, PITA customer who owns a High Power Tweed Twin 2x12. It is loud, and he is always fussing about how to make it less loud. He heard that two of the 6L6s can be removed, so we did that, but it's still too loud. He heard that one of the speakers could be disconnected, but as I understand it, half the power, half the impedence, but removeing a speaker doubles the impedance, so I told him no. Now he wants to get an attenuator, which I am not in favor of here, but it is his amp to blow up. I am sure he is going to ask if he can run it on two tubes, and although my gut says that is not a good idea, I am not sure.

Enlighten me?

then why people go buying a high powered amp if its too loud?
he could have gone 5e3 or another tweed model.
You can go MV,pre or post PI.
Or a simple scaling in the PI bias resistor.
I guess that the speakers are in parallel,so disconnecting one and taking off 2 tubes you should be ok,that will be 6 DB less roughly,plus you could make another 6dB attenuation with a couple resistors.

[Randall]

I never understand the part about how many tubes equates to how many speakers. I though when you remove two of the four tubes, you need to switch to half the impedence (when there is a switch). But, If there is no switch pulling one of two speakers balances things out? How?

Or another idea, can 6V6s be run in a Tweed Twin?

[Helmholtz]

Removing 2 of the 4 tubes doubles the amp's output impedance as the tubes were wired in parallel. So the 8 Ohm output becomes a 16 Ohm output etc.

[J M Fahey]

Above ideas are excelent but the easiest to UN-mod back to normal (do you think he won´t change his mind at random?) and to boot *effective* , you get as many dB down as you wish, no 3 or 6 dB by pulling tubes, mismatching, etc. . is to add a *fixed* attenuator.

IF he changes his mind, you easily mod to a new attenuation level in a jiffy.

Use a close to nominal resistor , full power, in series with speakers, so, say, 4/5 ohm in series with 4 ohm speakers is fine, and then you parallel whatever you want with speakers.
Say 8/10 ohm for minimal attenuation; 4/6 ohm to tame a stage flamethrower to a resonable large Club amp; 2 ohm for a garage amp, and so on.
You can go as low as 0.5 ohm resistor for a bedroom one.

As soon as he changes his minde (he will) , mod the parallel resistor to the new value you need, higher or lower.

You may also add a DPDT switch which *fully* removes attenuator out of the equation, if he ever plays in a large event or outdoors.

This is just a variation of my 3 AM attenuator.

[g1]

I never understand the part about how many tubes equates to how many speakers. I though when you remove two of the four tubes, you need to switch to half the impedence (when there is a switch). But, If there is no switch pulling one of two speakers balances things out? How?

When you remove 2 power tubes you are doubling the impedance on the primary side. So you need to double the impedance on the secondary side as well. If you have an impedance switch, you set it to half of what the actual load is.
Now the transformer 'sees' double of what should be, on both sides.

If, instead of using the impedance switch, you double the impedance of the load (by disconnecting one of the 2 paralleled speakers), you are accomplishing the same thing.

[Randall]

When you remove 2 power tubes you are doubling the impedance on the primary side. So you need to double the impedance on the secondary side as well. If you have an impedance switch, you set it to half of what the actual load is.
Now the transformer 'sees' double of what should be, on both sides.

If, instead of using the impedance switch, you double the impedance of the load (by disconnecting one of the 2 paralleled speakers), you are accomplishing the same thing.

Thank you. I can remember this. I'm not sure I totally grasp the why, but as a practical matter, this is enough.

[g1]

The why is basically that you need to maintain the ratio. Double on the primary side, then you need to double on the secondary side.

[olddawg]

Some people can’t differitiate loud from bright. I will deal with this tomorrow when I use an 18 watt open back combo and a compressor into the clean channel.... While the fool on the other side of the stage is grinding away through a JCM2000 and an oversized 4x12 cab my bass player will be screaming how “loud” the combo is when I use that channel. Go figure. ANYWAY... I would tell your customer simply that this is the way the amp was designed. You can’t make a horse into a cat. He either needs to get a smaller amp or use an attenuator/power soak. I use one all of the time. IMHO the Weber ones with the speaker motors work/sound the best. It won’t stress the amp any more than stressing it loud through speakers.

[Randall]

"I would tell your customer simply that this is the way the amp was designed. You can’t make a house into a cat. "

I did, in no uncertain terms, trust me. I also told him to back off with the freaking constant questions and 30 minutes of texting, because after all, I am supposed to get paid for this. Do your own research, I'm not your on call oracle. We'll see where that goes, it may have solved this problem.