This unit was purchased from the estate of an SK ham.
This unit was tested before purchase with an IC-746Pro and showed to put out
more than 600W with a 40W input. This was measure with a Drake W4 watt meter.
The antenna used was an Alpha Delta Fan Dipole.
The first goal was to replace the existing (original?) power
board and the capacitor array – The replacement is from Sunlight Energy
Systems, Mike Bryce – sold by The Heathkit Shop –
Removed the existing power supply board. In examining it,
it appeared that the original capacitors had been replaced, and there appeared
to be other modifications to the circuit board based on the jumpers soldered in,
resistors added in several places and the appearance of new looking solder in
other locations. The components on the board looked to be original (except for
the large capacitors) and in the proper locations. The new board was installed
making the connections per the manufacturer’s directions. Per the
manufacturer’s directions, the power divider that consists of four resistors,
mount on a terminal strip, attached to the center divider, was removed. The new
board has the voltage divider and the current shunt included.
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| Interior of the Clipperton - the green wires came off the power switch |
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Bottom of the original Power Board - notice the modifications |
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| The added transformer is circled in red |
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| Double toroids - found to replace FL1 |
The T/R relay appears to be after market. It has a blue
plastic cover, round base with a locating notch on the center pin for locating.
The manual states that this relay should be a 3-pole, double throw 12V constant
relay. The one found is a Guardian Electric, 1418 Series, A410-367-167-123. It
has a round base with 11 contacts. A Google search did not find an exact match.
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| Aftermarket relay replaces the original open frame style |
The power switch was not wired per the original schematic
– The original schematic indicate that the mains power switch should be in the
power (black) wire of the line cord. We found the switch was connected in the
neutral (white) wire of the line cord. Green colored wire was used to make this
change. During the replacement of the main power cord, we corrected this error
and wired the On/Off switch per the schematic, placing it in the black wire
line. It was also found that the Interlock switch (which should reside in the
white or Neutral line) had been removed. We did not replace the switch as there
was not any place to mount it. It appears that the Interlock switch and FL1
were removed to make way for the larger enclosed T/R relay.
A soft start power board – by Harbach Electronics – was installed
as per the manufacturers schematic. Basically, the board goes into both the
power (black) and neutral (white) wires of the line cord.
Power on test – All tubes lit. Voltage in both the CW-X
and SSB switch positions matched the numbers in the Dentron Clipperton – L
manual.
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| New power board in place - voltage divider is gone. |
Connection to the Icom IC-7300
RF output of the IC-7300 was connected to the RF input on
the amplifier. The RF out on the amplifier was connected to the transmitter
side of a Drake W4 Wattmeter. The load side of the Drake Wattmeter was connected
to a MFJ Cantenna dummy load.
The “send” RCA jack on the IC-7300 was connected to the
“relay” RCA jack on the amplifier. This connection had a mechanical relay in
the line to help isolate the radio from the amplifier. The relay is powered by
12 (13.8) VDC from the IC-7300’s external power supply.
The ALC RCA jack of the IC-7300 was connected to the ALC
RCA jack of the amplifier. A straight through shielded cable was used to make
this connection.
The IC-7300, set to CW mode, and the transmitter (IC-7300)
was set to 10% power out. A key down test to the amplifier (off) showed about
10 watts output on the Drake Wattmeter.
The Dentron Clipperton –L amplifier was turned on. The
band was set to 20M (14 MHz), the tune knob was set to 14, and the load knob
was set at zero (0). The amplifier mode switch was set to CW-X and the meter
was set to Vp, with the switch in STBY position.
Meter switch was changed to Lp and the switch set to OPT.
Keying the IC-7300 caused the relay in the “send/relay” cable to click, the
green power light on the amplifier to go out and a humming noise came from the
amplifier. There was no movement of the amplifier current meter.
The IC-7300 output power was raised to 30% output, and
keying the transmitter garnered the same results as listed above. Changes to
the tune and load knobs did nothing, and the wattmeter continued to show the
unamplified output of the IC-7300.
The voltage reading taken at the “Relay” RCA jack on the
amplifier, showed a voltage of -6VDC. Reversing the test leads, indicated that
the center pin of the Relay RCA jack was negative and the outside shell was
positive.
A continuity test was done on the “Send” RCA jack on the
IC-7300 while at rest. With a VOM set at RX1K Ohms, a reading of five (5) was
obtained.
A straight shielded cable was placed between the IC-7300
“send” RCA jack and the “Relay” RCA jack of the amplifier. A test transmission,
with the amplifier set as described above, yielded the same results described,
along with a burning smell from the IC-7300. The cable was immediately removed.
Troubleshooting
With the myriad of problems, all seemingly unrelated, we
decided, after reviewing the schematics of both the power supply and the RF
section, it was decided to start with the relay and chase down all of the
connections.
Using an Ohm meter, eyes/observation and some tugging on
wires, we were able to determine that this T/R relay was wired and operating
properly. During this step is when we found that the FL1 was missing. Tracing
the two small (RG174) coax leads it was determined that the dual toroids that
are attached to the outside wall of the amplifier were taking the place of the
FL1. That solved one mystery.
The next step was to find the cause of the negative
voltage on the Relay RCA Jack. Here the schematic helped us determine that two
connections to the main power board were reversed. Basically the 12vdc power
from T1 was connected to the wrong end of the relay circuit. We had connected
the “second brown” wire to a point on the board where the white wire from the
light circuit should have been connected. This resolved, the covers were
replaced and things setup to test.
Our test transmitter (Exciter) was a Kenwood 950??. The
Kenwood was connected by RF to the amplifier input. The amplifier RF out was
connected to the transmitter side of a watt meter. Antenna side of the watt
meter was connected to a MFJ Cantenna. The transmitter “send” was connected
with a straight cable to the Relay RCA on the amplifier. Starting at about 15%
power (about 20 watts) on the transmitter, we started our testing. Success on
our wiring as the transmit light on the amplifier came on. This was a step in
the proper direction. We noticed that the current meter stayed at zero, and did
not move when either the Tune or Load knobs were turned. Further observation
indicated that the watt meter was showing around 150 watts output. The watt
meter would change with the turning of either the Tune or Load knobs.
Now it was time to open the amplifier back up and see if
we could find the problem with the Meter switch or the associated circuit.
Carefully removing the top cover and making sure that the capacitors were
discharged, we started tracing the Meter switch circuit. We verified the
connections to the Power Board were in the correct places. We checked the
continuity of the wires from the Power Board to the switch and found nothing
amiss. Then my “Elmer” decided to try one last thing. He took a can of contact
cleaner and sprayed the switch down. After exercising the switch, the cover was
replaced, the amplifier powered up. Using the same Kenwood and the same
connections, another transmission was made and we found that the Meter with the
switch in the lp position worked perfectly.
Output power on the Kenwood was increased to about 40%.
On the watt meter we observed an amplifier output power in the 550-600 watt
range. We decided that the amplifier was working properly and all the cables
were disconnected and the amplifier transported to its home location.
Regarding the IC-7300 that we used in the first test, we
found that there was no continuity on the “SEND” RCA Jack during transmit. The
radio was boxed up and sent to Icom Repair Center in Michigan for diagnosis and
repair. Indeed there was damage, which required the replacement of the RF Unit Board. Thankfully not a real expensive repair.
As a final note, Gary (WA5TED) is now the owner of this unit. His amplifier died, so, this was a good fit.
73
Michael - KG5UMH
Gary - WA5TED
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