June 1997
67
Table 1
Ten-Tec Centaur Model 411 HF Linear Amplifier, serial number 01A10087
Manufacturer’s Claimed Specifications
Measured in ARRL Lab
Frequency coverage: 160, 80, 40, 30,* 20, 17, and
As specified (can be modified
15 meters; 12 meters and 10 meters by modification.
by licensed amateurs for
operation on 12 and 10 meters).
Power output: 600 W on SSB and CW, 80-15 meters;
As specified, except 500 W
500 W on 160 and 10 meters. 350-400 W on
measured on 17 meters.
RTTY or SSTV (depending on band).
Duty cycle: SSB, continuous voice modulation, at
As specified.
rated PEP output; CW, 50% duty cycle, no time limit
at rated PEP output (30 seconds maximum
continuous key-down).
Gain: Not specified.
Approximately 8 dB, typical.
Drive power required for full output: 90-100 W, typical.
As specified.
Spurious signal and harmonic suppression:
≥
48 dB.
Meets or exceeds FCC requirements.
Intermodulation distortion (IMD):
See Figure 1.
Not specified.
Power supply requirement: 120 V ac at 12 A;
As specified.
240 V ac at 6 A.
Size (HWD): 6
×
15.5
×
13 inches; weight: 40 lb.
*The FCC-specified maximum legal output on the 30-meter band for US amateurs is 200 W PEP.
for the RF input and output. The rear panel
also has an
ALC
input jack and an
ALC
CONTROL
. If you plan to take advantage
of the QSK (for some users, this will be
the main reason for buying this amp), you
need to wire your keying line through the
Centaur. This is accessible through RCA
jacks on the rear of the amplifier. If you
have a late-model Ten-Tec transceiver
with
TX OUT
and
TX EN
jacks (such as an
Omni VI), connecting these to the
KEY IN
and
KEY OUT
lines, respectively, takes care
of keying the transceiver for other modes.
For other transceivers, there’s a
PTT/VOX
jack. There’s a wing-nut connection for
ground.
The first thing you’ll notice when you
push on the
POWER
switch is that the whole
box will shudder a bit. This is disconcert-
ing, but normal. The next thing you’ll cer-
tainly notice is the rapidly increasing deci-
bel level of the cooling fan as it accelerates
to warp speed. As noted, Ten-Tec moves a
lot of air through this amp, and it makes a bit
of noise in the process. The high blower
noise level was the only major complaint
about this otherwise well-thought-out and
well-built economy amplifier. We checked
sound levels of some other amps and found
the Centaur to be noisier than even some
higher-power units. Ten-Tec acknowledges
that the fan is loud, but a spokesman said it
was a design decision to incorporate lots of
air flow. Ten-Tec says it’s been unable to
come up with a quieter means of doing so
that’s within economic reason and does not
compromise tube life and component lon-
gevity. Even so, many ops would probably
be willing to sacrifice some tube life for a
quieter-running amp. After all, new 811As
are relatively inexpensive.
The mini-toggle switch next to the
POWER
switch selects
STBY
(standby) or
OPR
(operate). By following the directions
Figure 1—The
Ten-Tec Centaur
Model 411 spectral
display during two-
tone intermodu-
lation distortion
(IMD) testing.
Third-order
products are
approximately
39 dB below PEP
output, and fifth-
order products are
approximately
45 dB down. The
amplifier was
being operated at
600 W output at
14.02 MHz.
Expanded Product Review
Report Available
The ARRL Lab offers an expanded
test result report on the Ten-Tec
Centaur Model 411 HF Linear Ampli-
fier that gives in-depth, detailed tech-
nical data on the amplifier’s perfor-
mance, outlines our test methods and
helps you to interpret the numbers.
This report includes full-power spec-
tral purity charts for each band and a
chart showing how it stacks up
against similar, previously reviewed
units.
Reports are $7.50 for ARRL mem-
bers and $12.50 for nonmembers,
postpaid. Request the Ten-Tec Cen-
taur Model 411 Test Result Report
from the ARRL Technical Depart-
ment, 225 Main St, Newington, CT
06111 (personal checks accepted).
For credit card orders only, call 860-
594-0278.
in the Operator’s Manual, any operator
who’s at all familiar with how a tube linear
like this tunes and works will pretty quickly
get the hang of the tuning procedure. If this
is your first amp, just follow Ten-Tec’s clear
instructions in the Operator’s Manual. The
main thing (as Ten-Tec warns) is to avoid
overdriving the 811As. This is one excel-
lent reason for including separate meters to
simultaneously read the 811A grid current
and plate current. By the way, the
LOAD
and
TUNE
control knobs had rubberized grips
and spinner holes. Their vernier action was
silky smooth.
Another of the front-panel toggle
switches lets you select
QSK
or
PTT
opera-
tion. For CW, the QSK was super. Other
ops—including those who take pride in hav-
ing a critical ear for keying—said it sounded
great. For a CW hand like me, not having to
shut off my transceiver’s full-break-in when
running the amp was a gigantic plus. On
SSB, the amplifier performed well too. No
splatter or distortion was noted by other sta-
tions, and our Lab tests indicated good IMD
performance (see Figure 1).
The built-in wattmeter is handy. The one
in our review unit measured to within ap-
proximately 10%, worst-case. It was most
accurate on 40 meters, where our Lab watt-
meter and the Centaur’s wattmeter agreed.
On other bands, it read up to 10% low.
Ten-Tec did quite a nice job on the
Operator’s Manual. It’s complete and to
the point. There’s a tuning chart to help you
get in the ballpark while tuning up, plus a
chart where you can record actual settings
for each band; a troubleshooting chapter;
detailed descriptions of most individual
circuit boards—right down to pictures and
PC trace templates; and schematic dia-
grams of everything. There was no parts
list detailing the values of components
called out on the schematics, however. In-
T
T
C
–10
–8
–6
–4
–2
0
2
4
6
8
10
–80
–70
–60
–50
–40
–30
–20
–10
0
Frequency Offset (kHz)
Reference Level: 0 dB PEP