Preamp Tubes – How To Fine Tune Your Amp

You can fine tune your tube amplifier with one tube substitution. The tube that you want to change is V1 which is the first gain stage preamp tube. You can tailor the gain structure with different tubes making your amp run cleaner or dirtier and also change the dynamics. For example changing a 12AX7 for a 5751 ,which has 30% less gain, your amp will be a little cleaner and be more scooped in the mids along with a little more chimey top end. You can identify V1 on your amp by looking at the back of the amp. The tube closest to the input jack is usually V1. On Fender amps it is to the right and on Marshall’s it is usually to the left. You can also open the amp and look at the chassis tracing the wires from the input jacks to the tube. On amps with two channels like a blackface amp you can experiment with both first gain stage tubes. On channel switching amps you may have to consult your schematic or open the amp up and look at the chassis. You can experiment with many different types to suit your taste and playing style. There is a tube substitution chart in the article “Preamp Gain Factors and Substitution Chart” on the Articles page.

Let Me Repair Your Guitars & Amps

The 300Guitars Shop

Billy Penn's 300guitars Shop located at 1L Executive Drive in Toms River, NJ will bring your guitars and amplifiers back to life! Specializing in guitar & amplifier repairs and restorations in New Jersey.

  • Guitar Repairs
  • Guitar Restoration
  • Guitar Amplifier Repairs
  • Custom Tube Amp Building
  • Guitar Pickup Rewinding
  • Guitar Amplifier Modifications

Click here to find out more

How to find me

View Larger Map


300Guitars Shop 1L Executive Drive Toms River, NJ 08755 Phone: 848-218-0362