"Over the weekend, I was curious why my 101D/205D were such hummers. Our SPVR heater supply is so clean, with noise in the low micro-volt range; plus the ultracaps are isolated from noise and offer a very still DC. Just to be sure, I ran the filaments off a battery and fed LIO from a custom battery supply. I had no inputs connected to make ground loops impossible. Still the hum was there. Then I decided to put tin foil around the entire glass bulbs and connect the foil to signal ground. VoilĂ , that solved the issue. So these tube types were picking up EMI. Other tubes I've been using are much less sensitive to hum pick-up but still, it can be heard with a few of them when one puts an ear right up to the woofer. In all cases, the tin foil trick solved the issue. Of course it looks terrible but I'm thinking that if I included something made of solid metal, then at least one has the option to place a cover over particularly the 101D/205D types to make them quiet - something along the lines of this but custom and offered in black or clear anodized. I need a ca. 3" Ø and 6" height to cover all applicable tube families."


"Next I tried a metal cylinder I had on hand. That took care of both hum and microphonics caused by exposure to sound waves; like that Pyrex glass you mentioned. If you knock on the chassis, of course it will still trigger microphonics. But as long as you don't actually do that when listening, it's no issue. What is from a purely aesthetic point is that you no longer see the bottles. With certain current-production 2A3 and 300B I tested, there's really no need for a sleeve cover. For the 101D/205D and perhaps some others which people want to try—and/or in conjunction with highly sensitive speakers—you would want the shield for the blackest of backgrounds. More soon."


In rapid succession, the demands of his DHT project had Vinnie retrace established tube lore with personal experiments. I'd seen Trafomatic's Experience Two integrated use grounded metal cylinders around more noise-prone driver tubes to operate their 300B triodes without hum; and many a small-signal tube in vintage gear arrive inside spring-loaded twist-lock covers to hold it in place, extra useful with horizontal mounting but presumably also to shield it from RF/EMI. Given today's escalating ultrasonic pollution from WiFi networks, cell phones and switch-mode power supplies, it's perhaps not unreasonable to think that so-called NOS tubes made in far earlier times could be more susceptible to these conditions than properly engineered current production specimens which ought to account for them as the blatant status quo?


Allnic Audio's Kang Su Park combines glass and wire mesh for some of his custom tube chimneys with vented metal tops. This would seem to accomplish the tin foil trick without hiding the bottles. It's a clever John Le Carré double cross between functionality and aesthetics. Allnic's custom shields show up in their $19'900 pure DHT preamp, in the matching $19'900/pr A5000DHT monos and in the gargantuan $89'000/pr A10000 mono shown. We appreciate that braving the not exactly common DHT waters can mean custom parts which, in small runs from boutique vendors, can complicate things on the production and bookkeeping sides. It's not like op-amps funded by Big Corporate, then repurposed for hifi use by small firms. If you want an attractive tube shield for a DHT; or a tube socket suspension - you'll likely have to roll your own.



After showing a pre-production version at Axpona, Vinnie had actual photos right after.


About the new power supply which replaces the stock ultracap charger, "it is ~6.5x9x3.75" WxDxH, black and weighs about 10lbs. Its umbilicals (one for the 24V power input, one for the DHT filaments) are about 5 feet. There's an on/off rocker with red power LED on the front which should be left on all the time. The DHT turns off when Lio is turned off via its front-panel or remote switch. There are heat sinks on the rear and a power IEC. The DHT module will come with the new DHT Output module with added PWR input jack for the filaments. There is no extra charge for that but we do ask that people return their stock Lio output module at their convenience."

 
The left tube supplies the right channel and vice versa
 
When a luckily insured box worth $4'000 of nude Vishay Z-foil resistors from Texas Components got lost in shipping with FedEx—at $15/ea., those resistors end up in the volume control module for the DHT conversion—my review loaner dispatch suffered a bit of a delay. But this actually helped it catch up with availability of the custom-made tube covers so Vinnie could ship everything out together. Which gets us at minimal housekeeping chores for inveterate and newbie tube rollers alike. They only must keep in mind to match their 3-position switches next to the tube sockets to the bottles they're plugging in. A 2A3 or 45 wants to see 2.5V. The PX4, PX25, 101D and 205D need 4V. The 300B, SR71A, SV811-20, SV572-40 and CX301A all want V5. Be mindful that the values of the left/right switches are inverted relative to each other. This graphic shows how. Mistakes here could take out a lovely triode so be sure not to rush or go momentarily dyslexic and get this right. It's simple enough but important.


Also, tube pins vary in thickness relative to the socket's female receivers. It's why Vinnie deliberately went with the premium Japanese Yamamoto sockets. They use split sleeves for each pin. Should you suffer bad contacts because your pins are too thin, use a jeweler's flat-blade screw driver to gently bend the socket sleeves inward. They'll narrow and the simple down force of insertion when you plug in the tube will create the desired tight fit. That's common mechanical sense but a little care can go a long way. As to stock tubes, "we ship a pair or electroharmonix gold-grid 2A3. They're very linear, extended and quiet." About 45 as my favourite DHT in the past, "I've tried a few NOS 45. They had a lot more hum. I need to try with the tube covers and see if that helps (it should). The EML 2A3 mesh plate so far is my favourite! I haven't tried the EML 45."