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Topic: Tube Amp with Power Cut? |
Isaac Stanford
From:
Philadelphia, PA
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Posted 31 May 2011 4:06 am |
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| Does anyone know of an amp manufacturer that makes a good pedal steel tube amp that has the ability to cut some of the power so that you could get a lower wattage with the same amp? Do I really have to buy two amps? It looks like victoria and carr use this in some of their amps but the higher wattage is still pretty low for pedal steel head room. |
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Franklin
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Posted 31 May 2011 5:16 am
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Isaac,
The Little Walter has that feature available.......Paul |
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Mike Neer
From:
NJ
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Posted 31 May 2011 6:16 am
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You can buy an aftermarket kit that will enable you to add this feature to tube amps (London Power offers Power Scaling). http://www.londonpower.com/catalog/about_our_ps_kits.php It is an extensive mod and should either be done by a pro or someone with experience.
_________________
Links to streaming music, websites, YouTube: Links |
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Ken Fox
From:
Nashville GA USA
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Posted 31 May 2011 6:20 am
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| Fender did it with the Pro Tube Series Twin amp. It merely cuts the plate voltage in half and changes the bias voltage. Had one in the shop for repair. Seen it on older Musicman amps as well. Same scenario. |
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Tim Whitlock
From:
Colorado, USA
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Posted 31 May 2011 6:27 am
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| I used to pull two of the power tubes out of my Twin Reverb to cut the power in half. Rather inconvenient so I had a switch installed that would cut them out of the circuit. It's a common mod for Twins. |
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Ken Fox
From:
Nashville GA USA
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Posted 31 May 2011 6:29 am
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It seems a good power attenuator would give you more control to dial in the "sweet spot" for your particular application.
some info here:
In conjunction with an electric guitar amplifier, a power attenuator is used to divert and dissipate some or all of the amplifier's excess or unneeded power in order to reduce the volume of sound produced by the speaker.
Contents
[hide]
1 Explanation
2 Description
3 See also
4 References
5 External links
[edit] Explanation
With tube guitar amplifiers, it is often desirable to produce distortion by overdriving the output stage. Under such a condition, the amplifier will produce at or near its maximum output power. By reducing the amount of power delivered to the speaker, power attenuators reduce to desired levels, the volume of sound produced by the amplifier.
The most common approach to power attenuation is the 'power soaker' approach. In a 'power soaker', a portion of the power is absorbed by the power attenuator (which is placed in circuit between the output transformer and the guitar speaker), while the remaining portion of the output power is directed to the speaker. An example of a common type of attenuator circuit is the L pad. A variable L pad is a power divider circuit that is designed to operate with a load in such a way as to provide an adjustable level of power to a speaker while maintaining a constant load impedance on the amplifier. [1]
A different approach, using a Variac or a power scaling circuit, reduces the B+ supply voltage available to the power tubes thus producing power tube distortion at a reduced level such that all available output power is sent to the guitar speaker. The Variac method is not without risk, as the reduced heater voltage applied to the tubes can damage the filament and/or cathode if not operated within the manufacturer's specifications. In a power scaling circuit, by decreasing just the B+ plate voltage, the cathode bias and screen grid voltage decrease proportionately, while the filament voltage stays constant. However the term power attenuator may be a misnomer for this type of power control because lowering B+ voltage tends to increase distortion, whereas according to convention, an attenuator should not introduce distortion.[2]
Power Damping is a method of output level control that involves the phase inverter and a potentiometer. The potentiometer allows that stage to be overdriven at reduced output similar to a Post Phase Inverter Master Volume (PPIMV) control.
[edit] Description
A power attenuator can be either purely resistive, or mostly resistive and partly reactive. The original guitar amp power attenuator, the Altair Attenuator, was primarily resistive, used a rotary switch to select taps on a toaster coil with low inductance windings. Another early model, simply called 'Power Attenuator' by Active Guitar Electronics, used continuously variable power rheostats. Other models, such as the Marshall Power Brake, add some electrical inductance or capacitance to the electrical load (including fans, light bulbs and coils). There is debate about whether reactive attenuators do a better job of preserving a guitar amplifier's tone.
A guitar amp power attenuator may also offer a line-level output jack for sending the distortion-processed signal through an effects chain, to a recording console, or for the purpose of re-amplifying signal through a larger or smaller amplifier.
If the amplifier is designed to accommodate being driven continuously at full power, the use of an attenuator will neither increase nor reduce the potential of damage to the amplifier. An early guitar amplifier to include a power attenuator was the Jim Kelley amplifier, which came with its own L-pad type attenuator. Some production attenuators are the Scholz Power Soak[3], the Marshall Power Brake, THD Hot Plate, and Weber MASS. |
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Isaac Stanford
From:
Philadelphia, PA
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Posted 31 May 2011 8:21 am
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| Thanks for the replies. Is there a reason that this feature isn't more standard on tube amps? It seems like it would be real useful. |
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Jim Peter
From:
Mendon,Mich USA
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Posted 31 May 2011 8:51 am
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My Mesa Boogie 50/50 power amp has a switch that will cut the power from 50 watts to 15 watts.
Jim |
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Tim Marcus
From:
San Francisco, CA
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Posted 31 May 2011 9:02 am
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there are a few ways to do this
1 - you can pull the two middle tubes on a twin. This will get you half the output wattage, but change the output impedance. And the bias voltage.
2 - you can put in a switch to cut power to those two tubes by simply lifting the ground (fixed bias only) which also affects bias voltage and output impedance
3 - pentode triode switch: this keeps all tubes in circuit and does not affect the output impedance. You basically re-configure the way the tube is wired with a DPDT switch. The result is half power, and a much grittier sound. Put a label on it that says "fun"
you can easily do any of these to any fixed bias amp like a Twin.
I don't really like half power for pedal steel. I prefer an amp that sounds good at low volume, and turning it down.
For guitar though, a twin with 2 tubes and a pair of 16 ohm speakers is a good sound. Very super reverb like - but with giant transformers!
_________________
Milkmansound.com |
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Tim Marcus
From:
San Francisco, CA
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Posted 31 May 2011 9:08 am
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| Isaac Stanford wrote: |
| Is there a reason that this feature isn't more standard on tube amps? It seems like it would be real useful. |
remember - 99% of tube amps are made for guitar players! Not pedal steel players.
What's useful for you/us is not useful for the manufacturers who have millions of guitar players to cater to.
_________________
Milkmansound.com |
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Isaac Stanford
From:
Philadelphia, PA
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Posted 1 Jun 2011 12:45 pm
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| Ken - Any recommendations for a good power attenuator? Any you know work well with your steel amp? |
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Ken Fox
From:
Nashville GA USA
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Posted 1 Jun 2011 1:33 pm
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I must admit I have never tried one. I have always tried to play in the clean area for Tele and steel, I guess I am a bit old fashioned! I have always used a compressor on Tele. Years ago I used an an old MRX Distortion plus, back in my wild and crazy youth!!
Still I can see where a good one should work well with any tube amp, mine included. Just make sure it can handle 100 watts of power.
Keep in mind the steel amp is a high powered tweed Twin with a few tweaks that I liked. Mainly things different:
-adjustable bias
-multi output transformer and ext sppeaker capability with auto transformer switching to keep impedance correct. I can actualluy set it up for 8 ohm or 4 ohm cabs
-ceramic power tube sockets for better heat dissipation
-adjustable power tube bias (like a 60;s Fender amp had)
-inrush current limiting on the AC primary side
-fused heater and 5 VAC supplies
-set up for a soldi state or tube rectifier |
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Ken Fox
From:
Nashville GA USA
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Posted 1 Jun 2011 1:40 pm
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Info from the net:
Explanation
With tube guitar amplifiers, it is often desirable to produce distortion by overdriving the output stage. Under such a condition, the amplifier will produce at or near its maximum output power. By reducing the amount of power delivered to the speaker, power attenuators reduce to desired levels, the volume of sound produced by the amplifier.
The most common approach to power attenuation is the 'power soaker' approach. In a 'power soaker', a portion of the power is absorbed by the power attenuator (which is placed in circuit between the output transformer and the guitar speaker), while the remaining portion of the output power is directed to the speaker. An example of a common type of attenuator circuit is the L pad. A variable L pad is a power divider circuit that is designed to operate with a load in such a way as to provide an adjustable level of power to a speaker while maintaining a constant load impedance on the amplifier. [1]
A different approach, using a Variac or a power scaling circuit, reduces the B+ supply voltage available to the power tubes thus producing power tube distortion at a reduced level such that all available output power is sent to the guitar speaker. The Variac method is not without risk, as the reduced heater voltage applied to the tubes can damage the filament and/or cathode if not operated within the manufacturer's specifications. In a power scaling circuit, by decreasing just the B+ plate voltage, the cathode bias and screen grid voltage decrease proportionately, while the filament voltage stays constant. However the term power attenuator may be a misnomer for this type of power control because lowering B+ voltage tends to increase distortion, whereas according to convention, an attenuator should not introduce distortion.[2]
Power Damping is a method of output level control that involves the phase inverter and a potentiometer. The potentiometer allows that stage to be overdriven at reduced output similar to a Post Phase Inverter Master Volume (PPIMV) control.
[edit] Description
A power attenuator can be either purely resistive, or mostly resistive and partly reactive. The original guitar amp power attenuator, the Altair Attenuator, was primarily resistive, used a rotary switch to select taps on a toaster coil with low inductance windings. Another early model, simply called 'Power Attenuator' by Active Guitar Electronics, used continuously variable power rheostats. Other models, such as the Marshall Power Brake, add some electrical inductance or capacitance to the electrical load (including fans, light bulbs and coils). There is debate about whether reactive attenuators do a better job of preserving a guitar amplifier's tone.
A guitar amp power attenuator may also offer a line-level output jack for sending the distortion-processed signal through an effects chain, to a recording console, or for the purpose of re-amplifying signal through a larger or smaller amplifier.
If the amplifier is designed to accommodate being driven continuously at full power, the use of an attenuator will neither increase nor reduce the potential of damage to the amplifier. An early guitar amplifier to include a power attenuator was the Jim Kelley amplifier, which came with its own L-pad type attenuator. Some production attenuators are the Scholz Power Soak[3], the Marshall Power Brake, THD Hot Plate, and Weber MASS. |
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Dan Tyack
From:
Olympia, WA USA
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Posted 4 Jun 2011 10:08 pm
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THD Hotplate.
It's the gold standard for power attenuators. |
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Cory Dolinsky
From:
Old Saybrook, Connecticut, USA
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Posted 6 Jun 2011 8:04 am
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i have a vht porweramp 2/90/2 with that feature. I love the amp i usually just use it on the higher setting.
Can you just switch in between the high and low power modes by putting it on standby or do you have to shut the amp off.
Cory |
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