Why are
processed tubes superior
to untreated tubes?

Cryogenic Process
Phase I - Selection

Cryogenic Process:
Phase II
- Treatment



    is here.

Click on any of the items on the left to learn more about
these superior sounding, cryogenically frozen tubes.

TubeWorld's cryogenic process takes select tubes and deep-chill anneals them for 36 hours at -193° Celcius / -320° Fahrenheit in a cryogenic chamber, producing a superior sounding vacuum tube called a

In stock form, a typical electron tube exhibits several problems that directly impact its sonic performance. Most serious are the many internal stresses in the construction materials that accumulate during most of the stages of manufacture and a very hard, heavy oxide-coating on through-glass pins to which direct connection is made. Seven (7) and nine (9) pin miniature tubes are typical of those pins that are heavily oxidized while power tubes such as KT88 and EL34 are fitted with bases whose pins are tinned with the result that contact quality is much improved. During cryogenic tempering, the tube is slowly cooled to the -193°C / -320°F temperature of liquid nitrogen (LN2), "soaked" for 36 hours, then slowly returned to ambient temperature.

By means of this unique and vital process, the stresses interior to the materials of the tube are substantially and permanently relaxed. The "Q" of the (self) resonant (electro) mechanical systems responsible for the output of (self) microphonic spuriae is thereby drastically reduced. By this important reduction, both the peak amplitude and the "ring down" time of these systems is reduced with the result that the "apparent gain" of the tube is increased - even in feedback controlled circuits - while the "dynamic noise floor" is lowered.

The sonic improvements of a over a "factory condition" NOS tube include:

TubeWorld selects tubes for treatment based on the following criteria:
1. Specific name brands that have superior sonics versus other brands.
2. Production years that have yielded the best sounding tubes.
3. Tubes with superior electrical characteristics as follows:

PREAMP TUBES (12AX7, 6922)

- Noise Grade: Low Noise or Gold Grade

- Dual triodes with close AC and DC section balance;
  most within 10%, many within 5% as tested on a SOFIA plate curve tracer

- Microphonics Test: Good (low) or Excellent (very low)

- Plate Current (ma) (will exceed specified rating)

- Transconductance (Gm) (at or above specified rating)

- Triode Section Balance Idle (DC) (within 1-10%)

Test Equipment used:

- SOFIA by Audiomatica plate curve tracer
- VTV Dual Triode Characterizer
- Custom Preamp: The design is full gain with no negative feedback;
   a very sensitive test to check tube noise and microphonics. Copyrighted
- Other test equipment listed soon

POWER TUBES (EL34, 6550, EL84, 211, 2A3, 300B)

- High transconductance

- Medium to high standing idle current

- Matched before treatment in triode mode and/or pentode mode

Test Equipment used:

- SOFIA by Audiomatica plate curve tracer
- Maxi-Matcher


- Tightly matched diode sections tested on SOFIA plate curve tracer

- Plate current as per specifications

Test Equipment used:

- SOFIA by Audiomatica plate curve tracer


The process is computer-controlled and consists of three stages:

1. Descend: 8 hours. Lowers temp from 65°F (room temp) to -320°F/-193°C.
2. Soak: 36 hours. Maintains a constant temperature of -320°F/-192°C.
3. Ascend: 8-10 hours. Raises temp very gradually from -320°F back to 65°F.

Tubes loaded in cryo tank

  • 211 GE 1940's
  • 6550A GE JAN 1985
  • GZ37 Mullard 1958-1959
  • CV378 High Wycombe
    England 1950-1952
  • 5687 Tungsol 1950's
  • 6900 Bendix 1950's
  • 5AS4 Mullard 1960's
  • 7025 RCA 1960's
  • 6X5GT RCA 194


STAGE 1, continued
Descent temperatures are displayed.

Temperature when lid was closed 16°C / 60°F (give or take):

Descend temperature after 6 hours:

LN2 valve on the cryo chamber is open, drawing precise amounts of LN2
into the chamber at specific intervals:



Top of LN2 tank after 24 hours:

Transfer hose connected to cryo chamber:

Temperature after 24 hours:



Ascend temperature displayed: