Hello, tube_guru here with safe tube substitution information for guitar, bass and harp players, with tube type amplifiers or preamps.

Musicians are very discriminating when it comes to tone, and distortion.The combination of the two is usually referred to as "tone". One of the most overlooked but easiest ways to make large differences in the way you amp sounds, is by tube substitution. What keeps most musicians from experimenting with tube substitution is fear of damaging your equipment. What follows are safe tube substitutions that can be performed without fear of damaging your amp.

The 12xx7 tube family has a lot of substitution possibilities because any tube that starts with 12 and ends with 7, or 7A, 7WA etc. and has the same bottle or glass dimensions, can safely be substituted without damage to your amp. What this will do is increase or decrease the gain of your preamp, which directly affects the amount and tone of distortion. The tubes that can safely be experimented with follow below. The tubes designated by numbers only, no letters,  are military or industrial versions of the standard tube types. Another point is tubes advertised as "triple mica" are more rugged and less prone to microphonics than standard two mica types and are found frequently on the military/industrial versions.

If your amp has one or more of the following tube types in it, any of the others can be substituted in the same socket. Written in a general order of tubes with the least to most gain.

least gain 12AU7-5814-5963-12AV7-5965-12AY7-6072-12AT7-6201-12AX7-7025-5687 most

Having a collection of these tube types in many different brands is the best way to experiment and find the tone you like. If you want more distortion substitute a 12AT7 with a 12AX7 or 5687 (extreme) Similarly blues players will find that often just different brands of the same tube type will affect the tone of their amps. Harp players may find that used tubes that are say in the 50% range, which would read as bad (weak)on most testers, gives the amp that mellow tone without harsh high end that is sought after. In short start collecting tubes and experiment!

A great source for tubes is my ebay store TUBE GURU's Vintage Electronics where unlike most other ebay tube sellers I guarantee most tubes with a no questions asked return policy. See listings for details. Drop me a message and I'll be happy to put together a small or large collection of tubes of various types and brands to experiment with for you, and list it at a reasonable price