Gettering Tubes AL572B AL80B


Gettering tubes 3-500Z, 572B,  and

 AL572B AL80B

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When I designed the AL80B and AL572 amplifiers, I included a high voltage
reduction provision. The transformer in each amplifier has HV winding taps that
provide 1/3, 2/3, and full voltage.

In the AL572 amp, the 2/3 tap can be used to run 811A tubes!!

When you buy new import tubes, it is a good idea to getter the tubes. You can
getter the tubes, or perhaps recover tubes that arc, by following the process below.


NEVER remove the cover with the
amplifier connected to power mains.

Never defeat the interlock.

Always verify high voltage is zero volts with the
front panel meter before touching anything.

WAIT for the bleeders to work.  If you ground the HV to
discharge, do NOT use a dead short unless the voltage is nearly zero on
the HV meter.

 Never run filaments below nominal voltage during

For filament voltage, see


1.)        Remove the cord from the outlet

2.)        Remove the cover

3.)        Locate the step start fuse near
the left rear corner and relay. Change the fuse to a 1-amp fast-blow fuse.

4.)        Locate transformer HV wires.
Normal connection is red/green to R/G, red/yellow to R/Y, and red to R (C21

5.)        Swapping R/G and R/Y without
moving red (red stays on C21) produces 2/3 normal high voltage

6.)        The layout pictured below
produces 1/3 high voltage. Provided you do not connect two wires to the same
point, there is no disastrous combination


AL80B AL572 getter 3-500Z 572B tube






It is OK to tack the wires in place, just be sure they do not easily pull













7.) Install the tube(s) you want to getter or burn in

8.) Install the cover and connect the amplifier to your radio normally

9.) Plug the amplifier in. Be sure the cover is on and has several screws
holding it on!

High voltage getter tubes reduced




High voltage should read 1/3 of normal


If the tube arcs at this voltage, it is “junk”. It will never recover.




















10.)        After confirming high voltage,
set your radio and the amplifier to 40 meters and run the PLATE and LOAD
controls nearly open.


Gettering tube 572B 3-500 tune and load





The idea is to keep the PLATE far from resonance.














11.)        Place your radio on FM or RTTY
on 40 meters, and bring up drive until you see about 200-250 mA plate current



AL80B gettering tube arc




You should have no or very little RF output.

Heat in the anodes is Ip times HV. In this case HV is 900 volts, and plate
current (Ip) is 250 mA.

Notice Grid current is about 1/3 of the Plate current. This ratio indicates a
good 3-500Z










12.)        Watch the color of tube
anodes. Anodes should be a very faintly detectable red. Do not run the tubes too


3-500Z half red






Look for the brightest part of the anode. In this case the anode is faintly
red. Adjust drive power and give the tube time to readjust color, and try for
barely red at the hottest place.

Run the tube like this 2 minutes RF drive on and 5 minutes RF drive off for
30 minutes. Do not turn filament off and on!

When finished remove RF drive and allow the fan to run for 10 minutes or
until exit air is not warm.

Unplug the amplifier, remove the cover, and exchange the red and R/Y wires.
This will place the amplifier at 2/3 voltage.

Operate the amplifier normally at normal maximum plate current for several
hours of normal use. This should be about half to 2/3 of  normal RF power


After this break-in period, if you have a recoverable tube, it should be good
at full voltage.