hot plate/powersoaks

[plexi]

I've run many different, if not all the major brands of attenuators in my many years of working with Vintage Amps. Of all those I've used, they generally have the same result. There is a flattening of brightness and an overall degradation of the sound quality. As transparent as those brands claim they are, I must be honest, there is no such thing as a perfectly transparent attenuator. There are a number of built in methods as well to help tame amp volume levels. The first that come to mind are the brands using the Kevin O'Conner system, Power Scaling. My own amp line, Mojave has a system we developed called Power Dampening. This is a good way to go with a new amp but it does not help with a valuable investment grade vintage amp and I would never prescribe or endorse modifying a vintage quality amp with an internal modification like Power Scaling or Power Dampening or anything else for that matter. Its destructive and devalues the product. The best solution is to find a safe and palatable way of getting the volume and tone to a point you like without ruining your amp. I do know that Mercury Magnetics does not want their OUTPUT TRANSFORMERS used with any attenuators. They have done their own investigating and feel that running attenuation is damaging to the transformers. I tend to agree with them since the truth is, the load is static and the transformer will not behave the same with loads such as an 8 or 16 ohm resistor or even inductive loads. The truth is, they don't sound that good either. If your amp is set to 16 ohms and your pumping 100 watts into a 16 ohm load attenuator, your theoretically matching your load to your amps Output Transformer. That is supposed to get you the correct frequency response and provide a natural effect. the truth is, that by the time you reduce the power level to the point where your satisfied with the volume, your more likely to be disappointed with the tone quality.

With respect to the Ultimate Attenuator there is a difference. The first palce this difference exists is the load resitor. The Ultimate Attnuator, also known as the "UA" uses a 30 ohm load resistor. I do not know exactly why that value was chosen, but I do know this. It's safer. A lot safer. Your amps power output is a mathematical equation. If you match the load to the ohmage tap on the transformer, say 8 ohms to the 8 ohm tap on the amp, your amp will provide maximum power efficiency. That means it works hard and will pass the maximum current. That also means heat. Heat in the Power transformer and the output transformer. That is because its passing loads of current. Dangerous for an old amplifier. This is not an ideal scenario for a vintage Marshall. The older original transformers were simply not designed for this kind of use or better yet "Abuse". With the Ultimate Attenuator, your amps current is reduced leaps and bounds.
For instance, if your amps set for a 8 ohm load, the UA is only going to see a maximum of around 25 watts made by your 100 watt amp. That is because the load is approximately 4 times larger. The result is the power amp is full throttle but the power output is low. That is good. It saves not only your output transformer but your power transformer. This is probably a good answer to the Mercury Magnetics concern now that the amp is not actually making any where near its full power even though the power amp is full tilt. The power transfered from the amp to the laod simply cant be any higher then the equation allows for.

Now what about the tone. The load is so far mismatched, how can the sound be correct? The UA has a built in low impedance power amplifier. The term low impedance means strong high frequency response and with their well crafted internal audio coupling, they have managed to retain and preserve the sound quality while keeping the amp at a low volume. The reduction of actual power is safer and the audio quality is preserved and enhanced via the audio coupling circuitry as well as the built in low impedance power amplifier, which does exactly what you need for low volume high frequency preservation.

Because of these two basic facts, the Ultimate Attenuator is definitely the safest product you can use and it delivers that low volume sound with the least impact which results in a very accurate quality of sound reproduction. For what its worth, this is just my opinion and my explanation was provided here to try and help some of you understand the way these things work.

Over the years, I have always told my customers that it was safer to use both a Hot Plate and a Variac together. The reason was simple, you can knock down the volume with the attenuator but you need to lower the power that is fed to the amp which results in how much power is made by the amp to protect it from catastrophe. I also recommended that the customer not use his best tubes since a variac will lower the heater voltage and thus reduce the temperature of the cathodes and that causes the preverbal Cathode Stripping, which simply put, ruins your tubes very quickly.

If your using an attenuator at present, I strongly advice you incorporate a Varaic to dial back the power level the amp can make. Reducing the power by 30 volts is enough to prevent catastrophe. The core temperature of the transformers can get very high internally and that will melt insolation between wire and cause shorts. The attenuator that is set way down for good volume control and even if it sounds good to you will be absorbing full power. Full power means full throttle on the current flowing through the transformers and full throttle on the internal core temperatures, several hundred degrees F. That can damage your amplifiers original transformers. Newer transformers like Mercury have developed improved insulation and with a quality improvement in over all design materials, they can withstand the increased core temperature much better but it's still a risk not really worth taking if you can simply avoid it.

The UA offers a higher load to start with and that makes it safer. You can mismatch a passive attenuator buy using a 16 ohm Hot Plate or similar attenuator on your amplifiers 8 ohm output tap, thus reducing the power in half, but the mismatch and the fact that your using a passive system will further erode tone quality if not dealt with some how. Again, the UA has adapted audio coupling and incorporates the low impedance power amp which resolves the tone issue.

I'm in no way claiming the UA is perfect but it does the best job to my ears and technically speaking there is a safety factor which is worth considering especially if you want to keep those old transformers from blowing or over heating.

I was informed that there is a protection circuit to prevent a major issue if you plug up your amp to the UA in reverse. That is to say you plug the output of the amplifier into the speaker output of the UA. That would result in a problem if there were no protection for that. Thanks to Tone-Freak, I have made the correction to my previous comments that you could have a problem with the UA because of its built in power amp. It's not an issue and that is very cool to know.

Sorry to admit it but I am guilty of this mistake. Thank God it was a passive Hot Plate. I did plug the amp into the speaker connection and the speaker into the amplifier input of the Hot Plate. There is no damage and no ill effect. The unit simply does not work as an attenuator. If you reverse the wires your back in business and all is well. one of the safer factors of a passive system.

For the money and trouble of buying both a passive Attenuator and a Variac and the fact that you will have to lug around an additional 13 pounds of iron using the variac and think about your tubes dying off, It makes a lot of sense to stick with the UA. The unit provides safety, good tone and you can use your best Mullard power tubes. The UA does have a 100 volt power outlet on the rear of the unit to allow you to run your amp 20 volts down for a good measure of safety especially if your using an old JMI that runs on 100VAC or 105 VAC. That goes for old Marshalls as well. We did many old Coffin logo, Block logo and Script logo Marshalls. They run exactly right at 240VAC but if you set them for US voltage, typically 105-115VAC on the back of the amps selector, they are over voltage at 120VAC. 100VAC is ideal for the older amps and will keep those internal voltage low enough not to blow up your original capacitors. Just another good reason to have the UA. When you guys use your older Marshalls or Vox amps or any British amp that was originally built for UK use, be sure to check this out or have someone check it out for you. You can see if your amps running hot buy measuring the heater voltage on pins 4 and 9 of the pre amp tubes. The ideal voltage for the heaters is 6.3VAC. If your looking at 8 VAC, you've got a problem and your running the amp with a very high internal voltage most likely. This is where a Varaic can help. It will lower the power down until the amps running at 6.3 Volts AC on the heaters. Now you can see where your amps AC input needs to be. If it sits at 100VAC, then that is the input you can safely use. If the running voltage works out to say 115 VAC input, your probably ok to just go ahead and run 120VAC since the difference is not outrageous and your not jeopardizing the amp. This is off topic but I mention it because the heaters reflect the internal voltages. That is to say if the heaters are way high, then your going to most likely have very high internal voltages inside your amp and then your in danger of over voltage on the old capacitors and putting tremendous stress on older tubes and power output will increase as well. Al these things are tied together.

That is my 2 cents.

[Bleuz me]

That is my 2 cents.

That was worth at least a buck and a half

[reece_26]

Thanks plexi, thats basicly what i was after.

[Roy Boltz]

Wow, you can't get much more detailed description than that. thanks!

[JFreden]

So, didn't mean to bad mouth the UA - I mean I have just bought one and I love the response and dynamics being preserved as well as the tone being much better to my ears than my HP. (Not to mention the two volume option which will make my life so much easier )

My point might be that you should get the "Plexi switch" to increase versatility and thus be able to use also in low volume conditions.

I'm gonna shoot Mark an email to see if it is a manageable thing to add a Plexi switch afterwards

[Britishampfan]

Thanks for the Info, I thought my hotplate was completely safe for use with my old Marshall. Have I gotten lucky with all the torturous use I`ve put my Marshall through?

After Plexi`s post I was willing never to use my hotplate again.

I love my old marshall, if the UA is that easy on it Vs the hotplate I would switch.

[plexi]

Thanks for the Info, I thought my hotplate was completely safe for use with my old Marshall. Have I gotten lucky with all the torturous use I`ve put my Marshall through?

After Plexi`s post I was willing never to use my hotplate again.

I love my old marshall, if the UA is that easy on it Vs the hotplate I would switch.

Please don't take my report the wrong way. A Hot Plate by itself will not do harm to your amp. I'm simply recommending that in addition, for older amps, a Varaic would be a good and safer bet to use in conjunction with your attenuator such as the Hot Plate. The Hot Plate or any attenuator by itself does not cause amp failure, its that you can push the amp beyond its capacities and that is where the danger lies.

[Britishampfan]

Thanks for the Info, I thought my hotplate was completely safe for use with my old Marshall. Have I gotten lucky with all the torturous use I`ve put my Marshall through?

After Plexi`s post I was willing never to use my hotplate again.

I love my old marshall, if the UA is that easy on it Vs the hotplate I would switch.

Please don't take my report the wrong way. A Hot Plate by itself will not do harm to your amp. I'm simply recommending that in addition, for older amps, a Varaic would be a good and safer bet to use in conjunction with your attenuator such as the Hot Plate. The Hot Plate or any attenuator by itself does not cause amp failure, its that you can push the amp beyond its capacities and that is where the danger lies.

Thanks for the reply and answering my concerns. Yeah I don`t demand cranked bedroom volume levels from my amp, all good sir and thanks.

[Tone-Freak]

Eric Johnsons amp tech told me that according to EJ a hot plate ruined the sound of one of his marshall's

[Roy Boltz]

Eric Johnsons amp tech told me that according to EJ a hot plate ruined the sound of one of his marshall's

Permanently? I never liked the way any of my Marshalls sounded with the hotplate, but I would never atribute the hotplate to be the cause. I thought maybe the Marshall circuit just didn't sound good being attenuated in genral. I didn't mind other amps with the hotplate, but the UA or HO unit does seem to make a difference & Marshalls sound better with them than the hotplate. Actually I find most amps sound better with the Ho type of unit, but more so with Marshalls IMHO.

[Britishampfan]

Eric Johnsons amp tech told me that according to EJ a hot plate ruined the sound of one of his marshall's

Eric Johnson is also a little nutty.

Add- Just so you all know, I have to try a UA attenuator now....sometimes info is a bad thing and ignorance is bliss.

[Tone-Freak]

I beleive the 30 ohm load is because when they first came out they only had a 100 watt load which was not enough for a 100 watt marshall so they recomended pulling two tubes. When you pull 2 tubes and run it on 16 ohms you need a 32 ohm load

[Tone-Freak]

Another thing about the UA I love is I can use it with any amp. I use it with my 100 watt marshall or my fender pro reverb.

[Magus]

Actually, the 30 ohm load was a very conscious decision. Ho didn't originally design the UA to be used with 100 watt amps. His original circuit was for amps under 25 watts. The 30 ohm load sounded best and was safest. The Ultimate Attenuator was developed from there.

[cedarchoper58]

Actually, the 30 ohm load was a very conscious decision. Ho didn't originally design the UA to be used with 100 watt amps. His original circuit was for amps under 25 watts. The 30 ohm load sounded best and was safest. The Ultimate Attenuator was developed from there.

weird why would you want to attenuate a less than 25 watt amp? i love my UA