How to improve the Fender 68 Custom Princeton Reverb's sound

How to improve the Fender 68 Custom Princeton Reverb’s sound without braking the bank. To make it more useable for pedals, and have more balanced and dynamic response, you can take a look at V1. This is the Tube that probably has the most influence on the tone and it also determines the rest of the signal flow.

Preamp tubes

As we look at tube amps for guitar, most of them carry a 12ax7 preamp tube in the first gain stage. A few exceptions are of course the Tweed Deluxe and the older tweed era Champs for instance. 

V1, or the first preamp might be one the most influencing on your tone and response as it also determines how your first amplified signal coming from your guitar goes into the rest of the signal chain.

12a tubes & Gain Staging

A brief overview on the different types of preamp tubes with each their own output rating.

The 12ax7: 100%

The 12at7: 60%

The 12av/y: 40%

The 12au: 20%

The Fender 68's Custom's V1

The Fender 68′ Custom Princeton Reverb comes with it’s 12ax7 in the first preamp stage. A princeton traditionally calls for a 12ax7 there, so that’s normal, you could say. 

However, the 68′ Custom tends to be quite an easy overdriving amp. The breakup is very early to perhaps give the player that vintage Princeton feel, which also breaks up early. Yet, a vintage Princeton sounds unreal and very beautiful when breaking up, and this reissue amp sounds both fuzzy and harsh. Why is that?

Well, to begin with V1 we have a GT 12ax7, which isn’t the best musically performing, but it’s also biassed very hot given we have modern wall voltages. Perhaps an truly ideal dialed in bias is possible. But still, you’ll have a compromise there as the circuit and components aren’t up to spec when compared to a hand-wired circuit.

The 'Mod', if that applies

By swapping the domestic average, or inferior first preamp tube by a higher quality one, for instance a JJ if we don’t have any nice RCA’s left laying around.

We also bring back the gain in V1 slightly by going to the 12AT7 type. From 100% to 60% you would say that’s dramatic, but it does a fantastic job. Not only do we shift the task of amplification a bit to other gain stages of the circuit, we also clean up the amp to where it almost behaves like a real Princeton does. 

We still have a lot of the amp’s own overdrive at our disposal, but it becomes more dynamic, more useful as a platform for pedals and to my experience harmonically more balanced. The high frequencies become more pleasant and three-dimensional, and the noise-floor comes down.

See and hear it in action

In this video we’ll do this mod to a Fender 68′ Custom Princeton Reverb and swap out our first preamp tube, a Groove Tubes 12ax7 with a JJ12AT7. 

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