Audio by Van Alstine presents The New AVA Ultravalve Vacuum Tube Amplifier
The amplifier that was rated "best bargain at the recent Rocky Mountain Audio Fest" by the senior editor of The Absolute Sound.
The Ultravalve is our lovely looking and playing pure vacuum tube amplifier with a polished stainless steel chassis and a gold anodized faceplate with black graphics and text.
The great grandmother of the Ultravalve amplifier is the original Dyna ST-70, no big surprise.We started taking a close engineering look at the ST-70 in the 1970s and were able to identify several design weaknesses that could be fixed at a rational cost. These included getting the bandwidths of the power supply, audio circuits, and input acceptance into the right set of ratios so that no input signal short of output clipping could drive the unit into gross distortion at any frequency. This made the feedback loop job much easier and the whole amp cleaned up a lot all the time.We also added a solid reference to the screen grid resistor and achieved even better stability.
We sold this upgrade as a complete do it yourself kit, our original Super Seventy amplifier, for many years. The kit also resolved the issue of aging and non-available basic power supply capacitors, and the value drift of so many of the original carbon comp resistors.
Next, we introduced the Super 70i when the supply of 7199 tubes dried up and we replaced them with 6GH8A tubes (identical performance, different pin-out). The Super 70i is really the grandmother of the Ultravalve amplifier.
After several more successful years with the Super 70i, it was time to re-evaluate the design again. By this time, we had come up with some unique successful power supply design ideas, some of which were applied to our highly regarded Transcendence Eight preamplifier.
We were able to incorporate these design ideas, namely a separate high voltage regulated power supply for each plate of each tube, into a brand new board design for the Dyna ST-70, our Ultimate 70 amplifier rebuild kit. However, by this time the supply of decent remaining Dyna ST-70 chassis were drying up, as were the number of audio users who dare still try a do it yourself kit.
It was time to rethink things again thoroughly.
What needed to change to produce a thoroughly modern and rationally priced vacuum tube amplifier?
First, we needed a complete new modern chassis. We worked with Dynakitparts to produce the chassis for us from our design in lovely polished stainless steel. Adding a gold double anodized bead blast finished faceplate from our local vendor finishes off the elegant looks of the Ultravalve.
The Ultravalve has a lighted power switch on the front. The back has premium input jacks, 5-way binding post output jacks on 3/4" centers for 4 ohm, 8 ohm, and 16 Ohm taps, a line fuse, and a captive 16 gauge polarized AC line cord. The chassis top has small pin jacks for bias adjusting and the bias adjust controls.
The basic internal wiring layout was just fine, providing low noise and stable operation, and working on the "no surprises" mode we mostly replicated the Super 70i chassis wiring layout because simply it works very well.
The audio circuits are built on a ground plane shielded double sided PC card. We improved the grounding to make sure the amplifier is very quiet, and we located the board inside of the chassis to protect the user from exposed high voltages, and to keep the circuits from being exposed to the heat of the output tubes.
With room for a better power supply yet, we were able to widen the power bandwidth to 3 dB down at 50K Hz and 5 Hz and still maintain our goal of no feedback related overload under any condition of use. More engineering math provided us with better solutions for the bandwidths of the feedback and coupling circuits. Our tube choice has kept up with all the new audio circuit engineering even better than expected.
The Ultravalve uses a 5AR4 rectifier tube, two 6GH8A small signal tubes, and four output tubes. We supply it with matched quad sets of EH 6CA7 output tubes, but EL34 or KT77 tubes can be used too.Power is 35 watts per channel, but you can use it where you would normally use a 100 watt solid state amplifier. It does a great job of driving our 85 dB efficient Salk HT3 speakers full range to reasonable levels. This is one amazingly wide band, dynamic, transparent and utterly musical amplifier. It just does not have typical vacuum tube power amplifier limitations.
The whole thing, except for some active and passive electronic parts, is made in the U.S.A.
Rated "best bargain at the recent Rocky Mountain Audio Fest" by the senior editor of The Absolute Sound, the Ultravalve is ready to markedly improve your home audio system too. The price is $1599 factory wired, plus $50 shipping in its custom protective "cocoon" packaging. It is ready to play out of the carton, no initial adjustments, burn-in, or set up necessary at all. We think you will love it.
Dimensions 13" wide, x 7" high, x 10" deep. Weight 31 pounds