reduce power on an AD30

[FleshOnGear]

The TH30 and Dual Dark both have half/full power switches as well as 2/4 tube switches. So you're both right.

I wonder about the volume difference between the AD30 and AD15. LPL says the AD15 is noticeably quieter, and I have to take his word for it, since I've never played an AD15. Is it possible the AD15 power section is running at a lower voltage than the 30? Is that maybe part of the reason it's quieter? If so, then halving the tubes in the AD30 won't quite get you there.

Jondog and fiveightandten, I get both of your arguments. I think the hardest part of adding the extra cathode resistors will be making room for them inside the amp. Since the amp uses a PCB, it might be tricky to physically insert them. It might not be that hard, but I doubt it's trivial. Generally I prefer trying options outside of modding the amp first. On the positive side, this particular mod won't prevent OP from using it normally in the future, so it won't need to be undone if it doesn't work as hoped.

Maybe OP can borrow a smaller cab, or get an attenuator and try it under a return policy. Try some options that don't leave a dent in your bank account before you make a final decision. In the end, the mod might be the most efficient solution. It won't cost you as much as a whole new amp.

[Jondog]

It could be modded by cutting two copper traces and adding two wires. You could put it on a switch too easily enough. Just have to remember to change the output jack.

[FleshOnGear]

Ahhh! I had to look at it for a minute, but I see it now. Good stuff! You need to put the tubes in staggered for it to work - V4 and V6 or V5 and V7. As far as I can tell, you wouldn't even need a switch to go back to 4 tubes. Am I wrong about that?

That is easy, and easily reversible.

[Jondog]

Ahhh! I had to look at it for a minute, but I see it now. Good stuff! You need to put the tubes in staggered for it to work - V4 and V6 or V5 and V7. As far as I can tell, you wouldn't even need a switch to go back to 4 tubes. Am I wrong about that?

That is easy, and easily reversible.

Nope, no switch needed. Switch would just allow the tubes to remain in the amp.

[fiveightandten]

The TH30 and Dual Dark both have half/full power switches as well as 2/4 tube switches. So you're both right.

I wonder about the volume difference between the AD30 and AD15. LPL says the AD15 is noticeably quieter, and I have to take his word for it, since I've never played an AD15. Is it possible the AD15 power section is running at a lower voltage than the 30? Is that maybe part of the reason it's quieter? If so, then halving the tubes in the AD30 won't quite get you there.

Jondog and fiveightandten, I get both of your arguments. I think the hardest part of adding the extra cathode resistors will be making room for them inside the amp. Since the amp uses a PCB, it might be tricky to physically insert them. It might not be that hard, but I doubt it's trivial. Generally I prefer trying options outside of modding the amp first. On the positive side, this particular mod won't prevent OP from using it normally in the future, so it won't need to be undone if it doesn't work as hoped.

Maybe OP can borrow a smaller cab, or get an attenuator and try it under a return policy. Try some options that don't leave a dent in your bank account before you make a final decision. In the end, the mod might be the most efficient solution. It won't cost you as much as a whole new amp.

There is indeed about a 20V to 25V difference in the plate voltage between the AD15 and AD30 (the AD15 being lower). I'd guess that pulling 2 EL84s from the AD30 would increase that difference to 30V or 35V. But that isn't the only difference between the amps.

You wouldn't need to add cathode resistors, you would need to replace them with resistors that are different values. So there isn't any additional space needed.

It could be modded by cutting two copper traces and adding two wires. You could put it on a switch too easily enough. Just have to remember to change the output jack.

That would work, for sure. I guess i'm just the kind of guy that doesn't like to perform intrusive mods like this, when there's a version of the amp that already makes half the power. Cutting circuit board traces is irreversible. I know I wouldn't want to buy an amp that had PCB traces cut and then bridged with wire or repaired. I don't know many people that would.

A lot of classic Marshalls were hacked up in the 80s because people wanted more gain stages. These days, things are different. There are so many amps available that will do exactly what you want them to do, I simply don't see the need to cut up a perfectly good amp, when you can sell it to buy the one that suits your needs, and still end up with extra money in your pocket (swapping AD30 to AD15).

Just my 2 cents.

-Nick

[jontheid]

It could be modded by cutting two copper traces and adding two wires. You could put it on a switch too easily enough. Just have to remember to change the output jack.

I'm a bit confused as how this is supposed to work. In my mind it still doesn't mean you can pull 2 tubes without trouble.

What you are doing here is re-routing the cathode current of V7 through R29, and the cathode current of V5 through R33.

Remember what that cathode current does? It (self-)biases the output tubes. It does this by generating a voltage across the cathode resistors so that the grid voltage of each tube is more negative than the cathode voltage (as the cathode voltage is now positive due to the voltage across the cathode resistor).

Now, imagine the above setup, with a poorly matched set of output tubes.
Imagine V7 is a very strong tube, thus conducting a lot. It generates a lot of cathode current. But that cathode current won't directly self-bias & cool down V7 (as it should) - it will develop a big voltage across R29 (which is not its cathode resistor any more!). This will then cause V4 and V5 to run cooler, which will then cause a smaller than normal cathode current to flow, which will then cause not such a big current through R33 (which is V7s cathode resistor), hence V7 will conduct even more strongly.

I just don't get it. Please explain what I am missing here.
Thanks,
Jon

[Jondog]

Well, hopefully anyone with a cathode biased is running a matched set of tubes. Also it's no different than the way the cathodes are wired in the Dual Terror/TH30. It would be the same wiring scheme as found in the AD15. Nothing is being changed electrically. Each cathode is seeing the same resistance, each anode is seeing the same voltage and current. 1 is 1 is 1.

Dual Terror

[jontheid]

I was just being thick. Not the first time. It is a lot easier to see on the Dual Terror schem. how it works, you are just pairing the tubes differently, the reason being that the 2/4 tube switching option does so by cutting of one 'push' and one 'pull' tube by making the cathode resistor be in series with a 100k resistor, cutting them off.

Apologies for my density.

It's actually a really clever bit of design. It means when you switch out 2 tubes you still have the remaining tubes sharing a 150ohm cathode resistor and nothing has changed. As you say, 1 still equals 1.

[Jondog]

The TH30 and Dual Dark both have half/full power switches as well as 2/4 tube switches. So you're both right.

I wonder about the volume difference between the AD30 and AD15. LPL says the AD15 is noticeably quieter, and I have to take his word for it, since I've never played an AD15. Is it possible the AD15 power section is running at a lower voltage than the 30? Is that maybe part of the reason it's quieter? If so, then halving the tubes in the AD30 won't quite get you there.

Jondog and fiveightandten, I get both of your arguments. I think the hardest part of adding the extra cathode resistors will be making room for them inside the amp. Since the amp uses a PCB, it might be tricky to physically insert them. It might not be that hard, but I doubt it's trivial. Generally I prefer trying options outside of modding the amp first. On the positive side, this particular mod won't prevent OP from using it normally in the future, so it won't need to be undone if it doesn't work as hoped.

Maybe OP can borrow a smaller cab, or get an attenuator and try it under a return policy. Try some options that don't leave a dent in your bank account before you make a final decision. In the end, the mod might be the most efficient solution. It won't cost you as much as a whole new amp.

There is indeed about a 20V to 25V difference in the plate voltage between the AD15 and AD30 (the AD15 being lower). I'd guess that pulling 2 EL84s from the AD30 would increase that difference to 30V or 35V. But that isn't the only difference between the amps.

You wouldn't need to add cathode resistors, you would need to replace them with resistors that are different values. So there isn't any additional space needed.

It could be modded by cutting two copper traces and adding two wires. You could put it on a switch too easily enough. Just have to remember to change the output jack.

That would work, for sure. I guess i'm just the kind of guy that doesn't like to perform intrusive mods like this, when there's a version of the amp that already makes half the power. Cutting circuit board traces is irreversible. I know I wouldn't want to buy an amp that had PCB traces cut and then bridged with wire or repaired. I don't know many people that would.

A lot of classic Marshalls were hacked up in the 80s because people wanted more gain stages. These days, things are different. There are so many amps available that will do exactly what you want them to do, I simply don't see the need to cut up a perfectly good amp, when you can sell it to buy the one that suits your needs, and still end up with extra money in your pocket (swapping AD30 to AD15).

Just my 2 cents.

-Nick

No problem with that. I modified and sold lots of amps, been up front about everything and never sold at a loss, and in some cases sold for more. Sometimes, these mods improve an amps build quality. I've actually had tubes blow the traces right off the board, their just very thin skins of copper, much more delicate than wire. Everyones different.

[Jondog]

I was just being thick. Not the first time. It is a lot easier to see on the Dual Terror schem. how it works, you are just pairing the tubes differently, the reason being that the 2/4 tube switching option does so by cutting of one 'push' and one 'pull' tube by making the cathode resistor be in series with a 100k resistor, cutting them off.

Apologies for my density.

It's actually a really clever bit of design. It means when you switch out 2 tubes you still have the remaining tubes sharing a 150ohm cathode resistor and nothing has changed. As you say, 1 still equals 1.

No apologies needed. If you hadn't questioned it, you wouldn't of seen it. Always good to learn. You can also see in the schematic of the Dual Terror how it switches the output taps at the same time on the switch. Theres 3 taps there 16 , 8 and 4 ohms. The 4 ohms acts as 8 ohms with the two tubes.

[jontheid]

You can also see in the schematic of the Dual Terror how it switches the output taps at the same time on the switch. Theres 3 taps there 16 , 8 and 4 ohms. The 4 ohms acts as 8 ohms with the two tubes.

Yes! Very nice bit of design.

[Randy Bass]

Wouldn't all of the effort of converting the AD30 to half power only result in a 3dB reduction in output? That seems like a lot of work to accomplish very little, especially with a giant orange elephant (4x12") in the room.

[Jondog]

Wouldn't all of the effort of converting the AD30 to half power only result in a 3dB reduction in output? That seems like a lot of work to accomplish very little, especially with a giant orange elephant (4x12") in the room.

Yes. I myself probably wouldn't bother. I had a 15w amp next to my Rocker 30 and the difference was minor. More clean headroom, but not much louder. I've owned a Dual Terror and a TH30 as well as Tiny Terror. Full power always sounded best to me.

[FleshOnGear]

Wouldn't all of the effort of converting the AD30 to half power only result in a 3dB reduction in output? That seems like a lot of work to accomplish very little, especially with a giant orange elephant (4x12") in the room.

Yes. I myself probably wouldn't bother. I had a 15w amp next to my Rocker 30 and the difference was minor. More clean headroom, but not much louder. I've owned a Dual Terror and a TH30 as well as Tiny Terror. Full power always sounded best to me.

Which brings the discussion back to less efficient speakers and/or an attenuator. That is, if the user of the amp thinks the master volume just isn't good enough.

The last years I've always been happy, having the amp in a clean/slightly crunch setting and feeding it with some pedals. At the moment and for the band I'm now playing in I'd like rethink this habbit and change to a different sound: I just need one very nice, dynamic and rich rhythm sound, which has some bite and a nice amount of gain, but not too much. Well, this sounds just like the AD30, right? But in fact: As probably everybody can agree, the AD30 comes to life if you crank the Master Volume to the max. But in my opinion, crank the master up and keep the gain back too much doesn't sound nice... Actually my problem is, that the amp with the big cab is just too loud and I think I would come around with only 15 Watts as well! So I was thinking about reducing the power. I have a 70ies Silerface TwinReverb and for this amp, it was no problem to just pull out 2 tubes in the power section and change the speakers from 8 to 16 Ohms, and the power was reduced to the half. But the Twin is an A/B circuit and the AD30 is an class A circuit. My question now is: Is it also possible to reduce the power of the AD30 by pulling 2 tubes? and using the 16 Ohm cab on the 8 Ohm output, cause there will be 16 Ohms on this output, right? And if possible, is it necessary to bias the amp again?

OP, if you're still with us, I want to ask you about the sound you're trying to get. You said above that everyone prefers cranking the amp, that you want less gain, but that you don't like the sound of the amp cranked with the gain low. I must say, I don't really know how making the maximum volume of the amp quieter helps this problem. What is it about the tone of the amp at low gain and high volume that bothers you? Not enough bass or too thin? Muddy or murky? Maybe if you can describe how it sounds to you, we can make other suggestions.

[Ronnie Robinson]

It seems crazy to me to even suggest intrusive mods that will destroy any resale value (and maybe damage the amp) when they only need to get an attenuator