This article provides some information about tubes in conjunction with the AC30 amplifier.
- The AC30 is a cathode based amp with auto-bias. This means, you do not have to rebias your amp after you’ve exchanged tubes – just exchange them and you’re done.
- You should always get a matched set of power tubes.
- Depending on the actual model, accessing the tubes may or may not require removing the amp chassis
Most amps can be improved by changing tubes. In many cases, factory tubes are not the best sounding ones available and the tone can be significantly improved by upgrading to better tubes. However, it might not be an easy task to find the right tubes for your amp and your personal needs. Even different AC30 models may react differently to different tubes. Moreover, there are a lot of tubes available and the possible combinations are barely limited. You may follow other peoples experiences and best practices, but if you want to find the right tubes for your taste, you should consider a decent amount of time to try and experience for yourself.
Effects of Tubes
Different tubes may not only change the tone, but also the amount of gain/distortion respecitvely the amount of headroom. Usually, the most significant improvements in tone can be achieved by changing the preamp tubes. But also the power tubes and rectifier tube (if you have one) have an influence. Different power tubes, the EL84 in the AC30s, can make the sound thinner or more full. That´s the main difference when we tried different factories (those were TAD, Mullard (new), JJ and EH). The rectifier, the GZ34 in AC30s delivers the DC the power tubes use. The main way they affect the sound is by the different output voltage they deliver to the amp. In our experience, the difference can be more than 50V between different factories.
Those tubes mentioned above, especially matched quartetts of EL84, tend to be expensive so you maybe don´t want to buy more sets than needed. Good news, preamp tubes (exept NOS (New Old Stock) tubes) are in general cheaper and have more impact to the sound. But this is also the bad news about it. To really improve your sound, it is necessary to buy different factory tubes, more than you will need in the end. If you want to use other types of tubes be sure they match the specifications and the socket-layout.
The number of preamp tubes in the AC30 varies between the models. Top Boost and Normal Channel mostly use ECC83/12AX7 tubes. If you´re not shure have a look in the manual or at our Info Page.
Let´s say we got 3 tubes for the channels including the phase inverter tube. Than you need at least 5 different tubes as basic for experimenting. Good ones we can suggest are TAD Premium, Tung Sol, Valvo (NOS), Telefunken (NOS), Genalex Lion, Mullard, Silvania. Try to get selected low noise tubes, it´s always worth the money.
After you got some tubes, take your time to experiment. Set each tube to a different position, one after another and you will hear while playing if it is better or worse. But be careful while changing tubes and switch off the amp each time you chance them and only catch the tube and no other components inside the amp. Let them cool down a bit, they can get very hot.
Write down the combinations that improve your sound and then take these combinations and check again to find out which one is best.
– the tube in V1 affects the sound most.
– high gain tube means in general more distorted sound and lower gain tubes result in a cleaner sound.
– low microphonic tubes are suggested because noise always becomes more after the sound passes another tube.
Basically, tubes not last forever but we must differ between preamp, power and rectifier tubes. If you like the sound and nothing is getting microfonic oder noisy, there is no need to change the preamp tubes.
The rectifier tube only needs to be changed if you feel the amp is not keeping its tone when playing hard chords. The volume may lowers when playing hard chords. This can be because the tubes are not getting enough voltage from the rectifier when stressed. Another indicator is a blown amp fuse.
Power tubes need to be changed from time to time. They slightly lose their brilliance and the amp sounds muddy or they fail completly. Depending on how often you play and how hard you push the tubes you need new ones after 3 months to 3 years. We recommend to change them at least every 3 years. You may not notice the lose of brilliance but you may be surprised if you plug in new ones how open and airy the amp sounds.
Feel free to use the comment function to share your experiences about particular tube setups in specific amp models. Let us know what worked well for you, what did not, and why.