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Ultravalve
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Absolute Sound Editor's Choice Award
Winner

2011 Absolute Sound Editor's Choice Award Winner.

Home
Ultravalve Amplifier

Ultravalve Amplifier
E-mail | Print |

Audio
by Van Alstine presents The New AVA Ultravalve Vacuum Tube
Amplifier

1/5

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
$1999
factory wired, plus $45 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

©
2011 Audio by Van Alstine