Guytron GT100 F/V

September 19, 2005

It has been said that the quest for tone is a journey and not a destination. One of the advantages that smaller amplifier manufacturers have is the ability to continue to evolve and fine-tune a design in response to real-world user feedback. Longtime GP readers may recall that I reviewed an earlier version of the Guytron GT100 in January 1998. Since then, Guytron’s head honcho and namesake, Guy Hedrick, has further refined the amp’s design, and the GT100 F/V reviewed here incorporates a number of new features that were developed during the intervening years.


The Guytron GT100 F/V may look like a typical two-channel 100-watt head, but hidden inside lurks a very unusual and innovative patented design. To create more dynamic, complex, and expressive overdriven tones, the GT100 F/V incorporates an additional low-power output stage between the preamp channels and its 100-watt final output stage. Picture a complete 20-watt amp with a classic long-tailed phase splitter driving two cathode-biased push/pull EL84s into a custom hand-wound interleaved output transformer driving a dummy load. Then picture sending the signal from that output transformer’s secondary winding straight into a plexi Marshall. That’s the basic concept of the GT100 F/V, but, as you can imagine, it has taken Hedrick years to refine it to its present state.

Hedrick gigs regularly, and over the years he has tweaked the design in response to his own playing experiences, as well as those of many of his customers. And, like many boutique manufacturers, he has fine-tuned many of these amps to meet specific tonal requests. These mods led to the development of the recently added Focus and Voicing controls, hence the origin of the GT100’s new “F/V” suffix.

The new Focus and Voicing controls essentially let you perform your own custom amp mods on the fly. The 4-position rotary switches give you the stock GT100 sounds when they’re set to the their first positions (straight up). The other positions affect various circuit tweaks that reshape the amp’s frequency response and dynamic characteristics in the following manner:

Focus Switch Positions
1) Stock, unmodified
2) Reduced EL84 fizz
3) Warm and smooth with reduced compression
4) Clear and clean, with lowest compression—like a 6L6 amp

Voicing Switch Positions
1) Stock, unmodified
2) More British voicing (more upper mids and highs)
3) More American voicing (rounder highs and flatter mids)
4) American voicing with low-mid boost

All of these changes occur after the individual preamp channels, and many of them alter the performance of the EL84-powered pre-output stage. Some positions also affect the range and operation of the global tone controls and the frequency response of later stages.

Besides the addition of this self-serve amp-modding capability, there have been some other less obvious changes over the years. The chassis is now made of stainless steel—its corners are welded, neatly ground and radiused, and it has chassis-mounted threaded inserts along with a stainless-steel bottom plate that’s secured with eight countersunk screws. The metalwork is gorgeous—this is one of the most skillfully made chassis I’ve seen—and because it’s made of stainless steel, it’s going to remain untarnished for a very long time. Besides looking great, stainless steel has the additional benefit of not transferring magnetic fields through the chassis like ordinary steel. This can reduce hum and other problems, and many amp geeks believe it can also help focus the tone. To further reduce hum, the new version also features DC heaters on all of the 12AX7s (earlier versions had DC heaters on only four of the preamp tubes).

The circuit boards have evolved considerably over the years, too. The current boards are labeled “Revision F,” denoting the sixth evolutionary stage in the amp’s layout history. While the earliest GT100’s had flying leads connected to individually chassis-mounted tube sockets and pots, newer versions have their pots and tight-gripping Belton sockets connected directly to the PC boards. Hedrick says this change lessened preamp microphonics and improved consistency and reliability.

Guy’s Night Out

While the GT100 F/V delivers the goods at both low and high volumes with uncommonly smooth, rich, and dynamically sensitive clean and overdriven tones, the new Focus and Voicing controls expand its tonal palette considerably. Channel A still possesses impressive Vox-like chime and jangle, and the F/V controls allow you greater control over the final seasoning. With its extra gain stage, Channel B still excels at higher-gain tones, but now you can fine-tune the amount of compression and low-end tightness. Together, these powerful controls offer an abundance of tone-tailoring combinations. The addition of the new Focus and Voicing controls, along with the other recent refinements, propel the Guytron GT100 F/V to new heights of tone-sculpting capability. This is truly a one-of-a-kind, world-class tone machine that, like a fine wine, keeps improving with age.

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