Rusky tubed bad boy transformer???
Bob Hutchinson, N5CNN
I'm going to
examine QRO Technology's legal limit ++ transformer and see if it is
capable of transforming Hams wallowing in low power mediocrity on the HF
bands into Hams of presence. (Presence meaning, or associated with:
attendance, occurrence, charisma, attainment, persona, appeal, allure,
magnetism, achievement, realization, - - or, in the Ham Radio world,
bad-boy RF power.)
Technologies has been building fine HF linear amplifiers for many years.
Ray Connin, QRO owner, has been building them a lot longer. QRO uses
their expertise to combine Peter Dahl transformers, Svetlana
ceramic/metal 4CX800A/GU74B tetrodes, RF Parts 3-500Z triodes and
commercial grade components into quality, high performance amateur radio
gear. The HF-2500DX price with OSK is $3,145.00 plus shipping from
Bryan, OH, which was about $65.00.
Click any picture larger:>>
Some assembly required
This HF-2500DX arrived in three boxes, small, medium (heavy) and large. I
opened the large box first to take care of "some assembly required" as
the tubes were in their own box, packed in the plate transformer space.
I removed the cover and removed the screws holding the left side panels
so I can get in close with the camera. After inspection of the Russian
military 4CX800A/GU74B tubes to make sure all pins are straight, I got
em all aligned, carefully applied force to seat both tubes and attached
a high voltage harness to each tube. No surprises.
sides of the amplifier are doubled walled. After removing the cover
these two inner walls are removable to allow great access to components.
This feature sure makes it handy for pictures. I only remove one side at
a time because for structural reasons. When assembled with the 1/8"
thick cover, the whole box is very sturdy.
Physical size is 20" Wide
X 19" Deep X 8" High. After installation of all component this QRO
will weigh 90 lbs., so I will install the plate transformer and
ancillary transformer after the photographic session and after I
move it to the test bench.
it's tent duty
With cover and left side inter panel removed there is good access to all
of the amplifier. Large windows in the right inner side panel allow good
camera access. I like the picture taking part. Instead of trying to
compose a picture on the tiny screen on the tiny camera, I cable to a 13
inch color TV monitor just to the left of the light tent. This is the
one pair method, requiring only one pair of glasses. You younger Hams
might be confused here.
After the main picture
session I reattached the left side panel and removed the right side
panel so I could photograph the Peter Dahl transformers in place, but
not bolted in.
have examined and photographed the innards of many amplifiers. I get to
see the construction, design and components up close, and I share all of
it with HRM browser and readers. All can see from the pictures that QRO
uses the very best components, usually of much greater capacity or
quality than necessary. Every component, assembly or harness installed
or secured to military specs. I believe you will agree that, if you or I
were to design and choose components to build our own amplifier, we
would build using the same good stuff that Ray Connin uses in these
amplifiers. QRO's slogan is "Built by Hams, for Hams."
soft start, in-rush protection stuff
No sissy, putt-putt 117 VAC household circuit can drive this one. The
mains power required is 200 or 240 VAC at 20 TO 25 amps. If you have
used a 240 VAC circuit for your smaller amplifier in the past on a
shared basis with some other appliance such as an air conditioner, you
may need to make dedicated arrangements to run this amplifier in bad boy
mode. Soft start current inrush protection is provided by two big,
healthy, 50 amp, not 25 amp, solid state relays that eliminate damaging
inrush currents for all components.
Like the QRO HF-2000 I reviewed last year, upon removing the cover I was
duly impressed with an item than denotes the care, attention and quality
built into a linear amplifier, the band switch. No miniaturization here,
Ray uses the real thing, a big, rugged ceramic Radio Switch Model 86 or
equal band switch that will handle the job. Big coils, big capacitors,
big toroidal 4:1 transformer output network, big choke, big everything.
The air variables have fine 6:1 vernier drives that make tuning and
repeatability to the numbers easy.
squirrel cage type blower. Noise?
Well, any time you have to force air under pressure around corners,
through a plenum chambers and through two axial/radial heat exchangers,
you can't get around the centrifugal blower. The blower must rotate at
high speed to develop the characteristic of their name. Ray has design a
two speed circuit utilizing a big resistor to slow the slightly
overcapacity blower down to a slower and less noisy speed for side band
yammer, yammer, yammer and 50CFM for the high speed switch position. For
the demanding, demanding mo-power and duty cycle, the high speed will
keep things cool.
choke is big and out of heat's way. I have seen a few plate chokes
burned up. They were too small and not out of heat's way. In glowing
tube amplifiers a small diameter choke adjacent to the tubes must be in
the direct air low. In metal ceramic tube amplifiers, the plate choke is
not usually in a direct air stream, therefore it needs to be bigger in
diameter so it wont overheat from operation that is not as it should be
Vacuum RF relay circuits provide T/R switching with great hi-voltage
potential reserve, fast make and break on the order of two or three
milliseconds, and less noise. QRO utilizes a circuit similar to the one
made famous by amplifier expert Rich Measures, AG6K, whose circuit this
writer has installed and used on three Heathkit SB220 amplifiers. If you
are not intimidated or bored by really technical
amplifier writings and projects
click here to the Measures web page.
Svetlana 4CX800A/GU74B tubes
I love the warm glowing glass
tubes. They radiate and conduct heat from the anode, which gets cherry
red or white hot, and the cathode, in all directions to every adjacent
object or component. These surrounding objects and components - case,
plate choke, wires, tube sockets, pins and coils accept and buffer or
store the heat as parasitic heat exchangers. I guess the professor would
want me to use terms like exothermic (gives off heat) and endothermic
(absorbs heat), huh? These components then give up their heat to the
cooling air that slowly and quietly moves past and makes it way through
the exhaust outlet.
Sounds kinda serene, doesn't it? Metal ceramic, indirectly heated cathode
tubes have an anode that gets really hot also. But the heat is
efficiently conducted direct to the metal parts of the tube and the
radial/axial heat exchanger fins. Little heat is transferred elsewhere,
it's all going to the aluminum fins. Serene can't describe the
aggressive process of high velocity pressurized air rushing though the
plenum and tubes, taking the heat right out through the exhaust. Works
Most amplifiers made today in this legal limit ++ class utilize either
3CX800 Eimac ceramic/metal triodes or
4CX800A/GU74B tetrodes. It appears that the future is the Rusky tubes.
Even though the Russian military tube, which has flooded the world
market, are Russian military ugly and without the Eimac brilliant bright
finish, they have economically captured most of the amateur legal limit
amplifier market. I recently noticed replacement Eimac 3CX800 tubes for
$525.00 on a couple of web sites. The Rusky ugly tubes are about $125.00
at the high end and $50.00 at street prices.
What's the difference?
Well, I believe the inter-modulation distortion and some other specs are
better for the Eimac tube. But, the Rusky tube satisfies the FCC specs
required for amateur amplifiers of this type. They also supply the owner
with peace-of-mind satisfaction of low replacement cost, if ever needed.
Screen grid over-current
amplifiers utilizing the 4CX800 tetrodes, this one has a trip circuit to
screen grid from excessive current. See below for more info.
plate voltage, screen grid current, screen voltage, everything but power
out monitoring. Tuning with just the screen current meter is much easier
than I thought it would be. Use your outboard watt meter for status,
power and self esteem feedback, and to keep big brother from beating
down your door and confiscating your bad-boy QRO.
The manual & extras
Superb, best of any amplifier maker. Extra case screws came with this
amplifier. Since this is the first time I have checked out this
amplifier I don't know if it has always shipped with extra screws for
the case. Except for Ameritron, I have never received extra screws with
any amplifier. Thanks QRO.
QRO guarantees it
Warranty: Two years 100%
percent parts & labor. Tubes are covered by the manufacturer for one
the power supplies?
of course. Plate and bias AC voltage is furnished by a lotsa watts black
from the El Paso King of amateur radio transformers, Peter Dahl. Ancillary
power for cathode heaters, control, relay, metering, etc is provided by
a separate robust Peter Dahl transformer.
power supply HV rectifier board contains twenty N5408 rectifier diodes
in a bridge arrangement providing 5,000 PIV capacity for DC smoothed and
filtered by eight 470uf, high grade electrolytic capacitors. Total
smoothing and filtering for the 2,750 VDC B+ is about 58uf.
The larger control board above the HV rectifier and filter capacitor
boards provides LV bias, screen trip and control circuitry. The smaller
circuit board mounted on the divider is the screen supply board. The RF
I/O and ALC circuit board resides in the ventilated box attached to the
rear wall behind the tubes. Metering board is mounted out of camera
range just under the meters and in front of the rectifier board.
Stainless steel and Teflon dominate here. Pictures tell the quality story.
But, does it light up? Does
Will it provide presence on
the bands? Will it transform timid stations? Does it have big brother
attracting, bad-boy capabilities? Let's see.
For HF RF power out our test bench is equipped with:
Coaxial Dynamics 83000A peak reading directional RF wattmeter.
Bird 43 directional RF wattmeter.
Coaxial Dynamics 81000A Directional RF Wattmeter.
These with same slug values, usually 2500 watt, connected in series with
a 3500 watt low pass filter, a 7,500 watt. antenna switch utilizing
Jennings vacuum relays for access to 3000 watt fan cooled dummy load
located outside of building, or 75M & 40M dipoles, and verticals for
higher HF frequencies.
Testing of wattmeters is performed by placing in series with the
wattmeters mentioned above for comparison.
Accuracy of measurement
We use the average of
the two wattmeters mentioned above. Both manufacturer's spec. an
available inaccuracy of + or - 5% of slug rating at a mid-scale reading.
This works out to be an error factor of + or - 125 watts at mid-scale.
The maker's don't even mention accuracy at close to full meter right
deflection. Remember, these wattmeters are the bottom of their line,
most inexpensive of the manufacturer's offerings.
Data below is grouped:
Screen grid Current MA
/ Plate Current MA / CW Power Out Watts
QRP Settings Column
Bad Boy Column
above was done with 15% duty cycle side band yammer, yammer, yammer in mind. The HF2500DX
manual warns against continuous operation at screen grid
currents in excess of 50ma.
It's not like tuning the glass tube amplifiers. Tuning for maximum output
(max. smoke) is not applicable here. There is no forward or reverse power
meter in this amplifier. Focus is on screen current, so I tuned it just
like the manual prescribes. I set both Tune and Load to zero, applied 50
watts exciter drive, got slight negative screen current reading, advanced
Load clockwise until slight screen current indicated. Then Tune
clockwise until 75 to 100ma indicated, Load counterclockwise until 25ma
indicated, Tune clockwise until 75 to 100ma indicated, Load counterclockwise until 25ma
indicated. After back and forth adjusting while screen current
monitoring a few times the Tune control will no longer increase screen
current. At this point, if you're power requirements are for SSB, the Load control can be set
for screen current between 25ma and 100ma. It's tuned to
resonance for the drive level just like the manual describes. For
conservative operation or for continuous high power modes, limit screen
current to 50ma max.
After performing the
start from zero procedure several times it goes quite fast, nothing to it.
I even quit watching the wattmeters. I tuned by the book, watching screen
current only, then referenced the wattmeters to find that resonance and
maximum power for the drive level had been achieved. For 70 watts and 100 watts
drive I just continued the procedure. I recorded the numbers for future
screen current instantly trips the over-current circuit and the fault
light comes on. I tripped it several times while learning the technique
for tuning this beast. A slight counterclockwise rotation of the Load
control and a touch of the fault button/lamp will get things going again.
Retuning by the numbers to overdrive settings and reducing the drive to
suit power requirements is a snap.
Radio status decisions
In the first paragraph presence was mentioned as a possible benefit of
ownership. Well, this one's got it. Just take your pick:
occurrence, charisma, attainment, persona, appeal, allure, magnetism,
achievement, realization, - - or, just bad-boy RF power. With little drive
this box can truly QRO. It is a "transformer" too. Including the two Peter Dahls the total is three.
Ray Connin, QRO
owner and designer, suffers from the overkill syndrome even though he has
never been a hunter. It appears he opts for excessive capacity in
components as a standard design practice. Example of this standard can be
found in items such as the 50 amp solid state relays for soft staring
everything. Most makers would use 20 amp or 25 amp component for "just
enough" capacity. The big band switch is three times the size used in
For a 10 watt
dissipation requirement Ray specifies premium 50 watt gold resistors with
finned heat sink, bolted to the case, where most makers would use less
expensive 15 to 25 watt types air mounted. This "overkill" can be seen
everywhere in the amplifier. If you and I were making an amplifier we
the best components such as those found in QRO amplifiers.
Click Here to buy QRO amplifier at ebay. Be sure and tell-em
you saw their fine product at HRM.
Bob Hutchinson, N5CNN
President and Founder
Wireless Industry Association
If you would like to
publish an article here contact Bob