If you own a 100W tube amplifier and want to reduce its power, you may have wondered: What happens if I remove two of the power tubes? Will it work? How will it affect the impedance? Which tubes should I remove? These are common questions among guitarists looking to lower their amp’s power for rehearsals or small venues. In this post, I’ll explain everything you need to know about this process, including how to do it safely and the best practices to follow.
Does this work for all tube amps?
This method works only with grid-biased tube amplifiers that have 4, 6, or more power tubes. Most 100W guitar amps fall into this category, making this modification simple and effective without requiring bias adjustments.
However, some 100W tube amps are not suitable for this modification. Mesa Boogie Mark IV and Mark V, for example, use power tubes with independent taps on the output transformer. Some amplifiers, like the Peavey ValveKing 212, have series-connected filaments. Removing a tube in these amps breaks the filament supply. Other models may fall into this category as well.
All tube amplifiers with cathode bias – common in models using EL84 tubes, like the Orange AC30 are not compatible. In cathode-biased amps, the bias is shared across all four tubes, so removing two will result in a very hot-biased amp. This can significantly shorten the lifespan of the remaining power tubes and even cause damage to the amplifier. For these amps, an external power attenuator is a safer option for reducing power.
How do I safely remove the tubes?
Before attempting this, always prioritize safety. Power tubes get very hot when the amp is in use, and high voltages are present inside the amplifier. Disconnect the amp from the mains and allow the tubes to cool completely – this usually takes 5 to 10 minutes. Only begin the process when the tubes are cool to the touch.
Which tubes should I remove?
In most amps, power tubes are arranged in a straight line. Typically, the first two tubes amplify one half of the signal, while the second two amplify the other half. I recommend removing either the inner pair or the outer pair of tubes as shown below
Never remove just one tube! Always remove an even number to keep the amplifier balanced.
As a safety precaution, after removing two tubes from your amp, test it on the clean channel with the master volume set low. Gradually increase the volume while monitoring the signal. If you hear a clean, distortion-free sound, you’ve done everything correctly.
There are high power tube bass amps, like some Mesa Boogie, Fender, or Orange models, which may have six or even twelve power tubes (e.g., the Mesa Bass 400+), you can reduce power similarly. However, because these designs can vary significantly, it’s best to consult the manual or ask a qualified technician for guidance.
What about the impedance?
When you remove tubes, the amp’s output impedance increases!
For example:
• If your amp’s output is rated for 4 ohms, it will now match an 8-ohm load with two tubes removed.
• If your amp’s output is rated for 8 ohms, it will match a 16-ohm load with two tubes removed.
What about tube life?
Removing tubes doesn’t reduce their lifespan. However, if you frequently use your amp with only two tubes, it’s a good idea to occasionally swap the inactive tubes with the active ones. This helps ensure their performance remains evenly matched and extends their overall lifespan.
Final thoughts:
Reducing the power of your amp by removing output tubes can be a practical solution. However, it’s essential to understand your amp’s design and follow the safety guidelines to avoid any damage.
I hope you found this post helpful! If you have any questions or want to share your experiences, feel free to message me.
Niki Hristov