What makes the Texas Tone 12™ different from a Princeton amp?

Recently, I was showing a new amp build to a friend of mine.  After telling him a bit about the amp, a 14W tweed style combo with tremolo, he rightly asked, “What makes your Texas Tone™ amp different from a Fender Princeton amp?”  It’s a good question.

The Princeton wasn’t in mind when I designed this amp, although I used to play through a mid ’70s Princeton (AB1270 with a 5U4 rectifier), in a band with this friend.  I used the Princeton both in the studio and on live gigs. I eventually sold that amp because I couldn’t get loud enough unless I had my Tele wide open on the bridge pickup, and couldn’t get good distortion unless I was using the neck pickup. Now the Tele bridge pickup wide open is not a bad sound, it’s just not appropriate for every song and every situation.

I often play my Tele with both the bridge and neck pickups together, and I often roll the tone control off a bit, no matter what pickup I’m using.  I like the flexibility.  I couldn’t get either the volume or crunch that I wanted. So, I went home, pulled up a Princeton schematic and did a comparison.  What I found is are some interesting thoughts about amp design.

Leo Fender intended the Princeton to be a student amplifier, using in teaching studios and bedrooms.  Of course, I’ve known many people who have used them on gigs and recording sessions, myself included.  In my opinion, it’s fine for not only its intended application, but for use on small gigs, such as coffee houses, and recording, as long as what you want is clean and bright.

So, here’s a synopsis of the differences between my Texas Tone 12™ and the AA964 black-faced Princeton amp. Compared to the AA964 black-faced Princeton, the Texas Tone 12™ has:

  • Cathode biased power tubes vs. fixed bias. The cathode bias I use is somewhat cooler than a 5E3 (the reference for tweed, low wattage, single 12” combo amps for blues and rock), as I find the tone to be much richer that way, and rich tone is what these amps are all about.  Better living through better tone, I say.
  • No negative feedback vs. negative feedback on the Princeton. NFB reduces distortion and gain, while slightly enhancing treble response by attenuating low frequencies. A feedback loop helps create a cleaner signal that goes into cutoff distortion at a much higher volume setting (which ties in with why I wanted to move on from the Princeton). The cleaner sound of NFB is good for clean headroom (a la black-faced Fender amps), great for country, jazz, and Hi-Fi. I find amp headroom in other ways.
  • A 12AU7 cathodyne phase splitter vs. a 12AX7. The single-triode cathodyne phase splitter is slightly-less-than unity gain (about 0.9), meaning there is no voltage gain (actually a slight loss). The 12AX7 tube triode is a voltage amplifier, while the 12AU7 is a current amplifier, and therefore more suitable to cathode follower/cathodyne applications, and can drive more current to the output tubes.
  • The Texas Tone 12™ operates at a higher B+ voltage, and has a beefier output transformer.  Since cathode biased amps tend to have less output power than fixed bias amps, all other things being equal (which they rarely are), the higher voltage level gives me more flexibility to help recover some of that loss while operating at a more reasonable bias than the hot-biased Fender tweed amps. Besides richer tone, the slightly cooler bias leads to longer power tube life. The beefier output transformer has a richer tonal response and more power handling capability.
  • A Jensen speaker that is both higher end and larger (C12Q vs. C10R) than the one on the Princeton. The result is a louder, fuller tone.
  • A subtle and full range discrete Tone control and independent Volume control vs. interactive Volume, Treble, and Bass controls. Easy, full range of tonal coloration and less insertion loss.  It’s not quite as “bright” as a tweed 5E3, although brightness is not lacking.  I get it back in other ways.

Both amps use a grid bias tremolo, although the component values are different and the Princeton acts on fixed bias power tubes while the Texas Tone 12™ acts on cathode biased power tubes. As far as the tremolo goes, everyone who has played or heard this amp raves about the tremolo.

The combination of higher voltages, a 12AU7 PI, reasonable cathode bias, no negative feedback, a beefier output transformer, and a larger, louder, full-range speaker enable the Texas Tone 12™ to be amazingly dynamic and touch responsive, while the single Tone control allows the simple freedom of varying the amount of warmth or sparkle. When the University of Illinois Physics department did an analysis and upgrade of a Weber 5E3 kit, they found that, after their many mods, “the sound of the amp was great, but in many instances the amp without the feedback loop sounded more interesting.” They go on to elaborate. I concur.

Better living through better tone.