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Was he certain he’d left nothing to be desired? I challenged Tommy. "Buyers get what they pay for. Better quality parts can improve the sound and won’t hurt our reputation. But of course each designer has his or her own way of thinking. Personally, I use the best components my budget allows. If I cannot afford the parts, I have to decipher the know-how and manufacture my own. The parts I invested in the JB3 speaker for instance are getting close to absurdity. The new binding posts will be cryo-treated and are very close to WBT in performance. My only regret is that I can’t source the same high-purity copper they’re using. In the TL66, I have thought about using aluminum resistors but they don’t offer the impedance and wattage ratings I need except for special orders. I don’t have the quantity to justify such luxury. Cement resistors were a reasonable option and they do sound good for what they are. After all, I’m not selling astronomically priced products but high value."

Tommy’s biggest design challenge was the AC voltage supply to the grid long known to many DIYers as a tug of war between musicality and noise. For full-flavored SET sound, AC grid drive is regarded as mandatory (DC drive can be more complicated and expensive to produce). But the low-power output of a SET might expose a high S/N ratio with speakers of 95dB+ sensitivity. The trick lies in a carefully mapped point-to-point topography and a discrete power supply. Tommy’s custom power transformer runs two primaries to supply 6.3V AC to the 6L6 and the 6AU6 separately instead of a parallel supply from the same winding. Hence the TL66 delivers discrete supply voltages to each tube. The next critical component is the power filter capacitor.

The TL66 offers four high-voltage AC power filter capacitor configurations: Hitachi 220µF (basic), BHC Aerovox 220µF (good), BHC Aerovox 470µF (better) and Evox Rifa 220µF (best). My review loaner had the British-made BHC 220µF. Tommy sent me a photo of the Evox Rifa PHE169 version he’s using and elaborated on this Swedish-made electrolytic. "This is the mother of all capacitors, with high performance, low ESR and ESL and super-long life. Very few audio manufacturers would invest in these expensive components. I’ve seen them in Audio Nord’s Dali Gravity power amp, Gryphon’s DM-100 and REF-1. They are nicknamed canned pineapple here because of the size and liquid sound they make when you shake them. They can handle humongous current and charge and discharge at lightning speed to make them ideal for ultra-wide dynamics and inexhaustible bass reserves. But it’s not just the low frequencies that benefit. Most electrolytic capacitors have considerably high internal equivalent inductance and resistance that cripple high-frequency performance. Rifa has uniquely low ratings in those areas to result in naturally open extreme highs."

The higher the price tag, the better the performance? Tommy’s retort was "personal taste". Rifa excels in the high frequencies with exuberant tone colors and details; BHC is texturally rich in the midrange and Hitachi sweet overall with a still convincing midrange. However, DIYers are not encouraged to roll capacitors alone because other components should be modified accordingly like the feedback resistor.

Apart from power filter capacitor options, there are also three grades of coupling capacitors to choose from: TPX (good), TAPX (better) and TCPX (best), all JohnBlue’s own models. DIYers will crack the code in no time: T = Teflon, P = Polypropylene, A = silver foil, C = copper foil and X stands for mixed. My loaner originally ran TPX but Tommy sent me the TCPX to mod alongside with matching Allen Bradley resistors to replace the CGW resistors.

First I only replaced the coupling caps and broke them in for a few weeks. There’s good reason to believe that the simplest and fastest way to mod is by changing the coupling caps especially in such simple circuits and T-amps. The most noticeable improvement was airiness. The musical presentation became unrestrained and unbridled to set free a wide open soundstage. However, I also noticed that the presentation was somewhat more delicate and lighter than before. I informed Tommy who responded: "It’s time to replace the resistors." I'd almost forgotten about those. Luckily I found the Allen Bradley resistors and replaced the CGW. Another round of breaking in later, I had that weird feeling that Tommy was spying on me and knew everything one step ahead of me. There seemed no point telling him that I really loved what I heard. The AB resistors put the rich midrange back where it belonged. Well, I did tell the man. But this time he surprised me: "Usually I will match CGW with BHC and TCPX but in your case I think you’ll like a bit more midrange." Indeed.

It was time to take it to the next round of partnering ancillaries. Instead of running the Micromega Microdrive and Deltec Little Bit Bitstream DAC as source, I tried both the Micromega Variodac (with preamp) and the KingRex Preamp. I also had the Klipsch Synergy F2 replace the JohnBlue widebanders. Not to slight miniature widebanders but for Mahlerians and Stravinskians, this was the only way to real symphonic presence. You can’t argue once you hear them side by side. If the TL66 could put up this kind of performance with the Synergy F2—a low-fi high-efficiency speaker—I’m sure it could only get better if you raised the stakes in the speaker department. Somehow my attention was more on the partnership between pre and power amp though. Would the performance improve further if I eliminated the volume control?  

I expressed my concern to Tommy and he emailed instructions to rewire the signal path between RCA input and volume control for better compliance with a preamplifier. Before the mod, back ground hum was higher and I had to carefully set the volume of the TL66 in relation to my preamp to keep it at bay. After the mod, I could fully crank the TL66 and still feel comfortable although my preference was to leave it at around 3:00 and allow for some leeway for left and right channel balance in case it was needed.