Tube amplifier modifications


Because tube amps are rather simple to design and build, they are offered by a lot of companies. Most of these companies don't have the knowledge or available investments to get most out of the circuitry. A good balance between amplifier topology and component quality is crucial for getting a overall satisfying result. Just substituting a capacitor into a top-of-the-notch Black Gate might change the sound, but might not be the best improvement that could be achieved for that budget. TentLabs has a lot of experience optimizing an amplifier given a certain budget.


TentLabs has more than 20 years of experience with tubes, ranging from modifying amplifiers to researching the linearity of directly heated triodes. I worked with many different brands:

• Aristona
• Audio Innovations
• Audio Note
• Audio Research
• Bang & Olufsen
• Beard Audio
• Bocama
• Conrad Johnson
• Copland
• Dynaco
• Grant Lumley
• Harman Kardon
• HeathKit
• Jadis
• Lafayette
• Leak
• Magnatone
• Marantz
• McIntosh
• JoLida
• Philips
• Radford
• Ray Lumley

Besides modifying amplifiers, I still design and carry out fundamental research on tubes and tube amplifiers. In addition, modern components allow for optimised circuits where even semiconductors sometimes find their place. Time for some upgrades!

Modification Levels

I distinct 3 levels of modifications throughout any tube amplifier:
1. Upgrade of parts. Caps, tubes, resistors, whatever is inside and needs improvement.
2. Improvement of initial circuits, phase inverter stage, penthode output into triode conversion
3. Architectural upgrade and change of initial circuits. In the most extreme case this comes down to rebuilding the amp, but keeping chassis, transformers etc in their place.

Upgrade zones

Within an amp, various zones are present:
1. Input stage / Driver
2. Output stage
3. Power supply
4. Peripherals (volume controls, switches, connectors)

Obviously, it depends on the amp and the owners wishes (and budget) what to do, where to start, and what money to throw in where. Practice shows those different zones need different level treatment, to come to an optimally balanced result, in line with your taste and requirements.


A worked out example on the Web shows the modification of a Classic 25, which includes a lot of TentLabs suggestions (and soldering).


Please contact me at for a dedicated approach for the upgrade of your existing tube amplifier.