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[HAMHOCK75]

In reply #24, the location of the adjustments on the main board were identified. Recently, I found that other hams had created an adjustment procedure at this link,

https://www.qsl.net/icom/download/ic2kl_align.pdf

I have not done the complete procedure yet so I can't say how well it works. In some instances like the idle current, a different procedure was used so the match of the idle currents for each device in PA1 and PA2 could be plotted.

[HAMHOCK75]

While waiting on parts, I took apart the power supply to examine how it manages the inrush current. Like the 2KLPS, it is a two step process. The initial inrush current is limited by the input filter components and thermistor NTC1 ( p/n HPN 2R5D15 ) which measures about 2.5 ohms at room temperature. There is a winding ( yellow wire ) that when rectified by a two diode, packaged D10 creates about +13.8 VDC to charge C14. As C14 charges it turns on relay RLY1 which shorts out NTC1.

The rest of the schematic is of the temperature controlled fan circuit.

[W9IQ]

That is a nice hybrid step start circuit. It eliminates the need for the fail safe fuse seen in the typical amp step start circuit yet it removes the inefficiency of the NTC once the circuit is running.

Still enjoying your blog and the great graphics. Keep up the good work.

- Glenn W9IQ

[KM1H]

That is a nice hybrid step start circuit. It eliminates the need for the fail safe fuse seen in the typical amp step start circuit yet it removes the inefficiency of the NTC once the circuit is running.

Still enjoying your blog and the great graphics. Keep up the good work.

- Glenn W9IQ

Inefficient is an under statement. Many use them in boatanchors with the hope it will save their transformers while leaving the thermistor in a cramped under chassis already hot environment. There have been several reports of smoke and damage over the decades.

Carl

[HAMHOCK75]

The only part I do not have on order is the 50 degree C thermal sensor by Tokin.

Tokin must have been acquired by Kemet a some point. Kemet lists the part as OHD3-50M but it is sold with the Tokin name on it. The "M" means it is open until 50 degrees is reached at which point it "makes" the connection. There a "B" version which is the opposite, it "breaks" at 50 degrees C.

They are available through distributors like Digikey and Allied mostly for around $8-13 in unit quantities. 

https://content.kemet.com/datasheets/KEM_SE0202_OHD.pdf

P.S. Thank you W9IQ for the encouragement.

[HAMHOCK75]

I had to re-order the rear panel power connectors after the first order did not arrive but it was worth the wait.These connectors seem to have a generic name as L6.2 connectors where the 6.2 is the mm. between pins. They mated perfectly with the connector on the back of the 2KL. Total cost of all the parts in the photo was less than $6 including shipping.





Icom used two red wires inside to two pins and two black wires to two pins to the rear panel six pin power connector to distribute the current. To mate to that connector, black and red 12 gauge silicon wire was used. The wire was split at the ends to form two pigtails which were crimped to the female pins. Clear heatshrink was used over any exposed wire of each pigtail, then a piece of heatshrink was used over the main wire to cover the exposed wire at the Y between the pigtails.

Below is a photo of the silicon wire which is composed of very fine wires making it very flexible. It has the look and flexibility of Fluke DVM test lead wire.



While waiting on the connectors, the power supply was painted black to match the 2KL.

[VR2AX]

Congrats with your rebuild. What do you plan to do with it? I remember selling mine around 2006 along with a new unused AT500. Are the pinouts the same?

[HAMHOCK75]

VR2AX,

I am slowly getting there but there is still much exploring to do. The 2KL is fully functioning but parts are still coming in like the Tokin 50 C thermal switch.

As for the pinouts on the rear panel power connector, I could not find any identification pin numbers or manufacturer markings on the original factory connector at all. Same with the replacement parts. Since I did not remove the two wires for the front panel on/off switch from the factory connector, I used those connections identified on the schematic as going to pins 3, 6 as reference so pins 2, 5 go to the +40 VDC, and pins 1, 4 are ground.

Funny you show mention that you had the tuner. I just acquired that tuner from an estate on Saturday. Yesterday I was able to test it with the Icom 7100. It works perfectly and is very quiet in operation. I bought it because it can handle 500 watts continuously. My LDG AT-600ProII cannot do that. For digital modes it is limited to about 250 watts.



In the photo is also my SB-200. It needed the relay contacts cleaned. While doing that really brought back how different the 2KL and SB-200 are. The 2KL is close to the complexity of a modest rig like the Ten Tec Century 21 CW transceiver. The SB-200 is much simpler. I suspect this means going forward with solid state amplifiers that fewer hams will be able to service their amplifiers.

The amplifiers are continuing to get more sophisticated too. Elecraft's KPA1500 manages to get 1500 watts pep output with the tuner in a package just slightly larger than the 2KL by itself. Price is about $6,200 new.

I also recently came across a schematic of the RF portion of the popular Mercury IIIs.



While the 2KL has a 3 dB attenuator at the input followed by clamp diodes to protect the input, the Mercury has has a 17 dB attenuator ( 7 dB comes from the "T" attenuator formed by R2,3 in series with R4, 5 with R7, 8 in shunt ) followed by clamp diodes.

This is a link to "T" attenuator values.

https://www.electronics-notes.com/articles/radio/rf-attenuators/pi-t-bridged-resistor-values-table-calculator.php

So a 100 watt input is only 2 watts by the time it reaches the actual devices. Since it is stated that only about 50 watts is needed for full output, assuming for a moment that would be 1 kW CW, then the device gain must be in the neighborhood of 30 dB which is considerably higher than the 2KL's device gain of about 13 dB.

The clamp diodes are not ordinary diodes but diodes designed to protect against electrostatic discharge.

https://www.mouser.com/datasheet/2/389/cd00000725-1795467.pdf

A demonstration video blasting the input with 100 watts.

https://www.youtube.com/watch?v=CfDO0VNVvnU

Meanwhile I am starting to examine how the 2KL's other protection circuits work.



 

[HAMHOCK75]

Solid state amplifiers could conceivably be simpler than tube amplifiers were it not for all the protection circuits. Below is a simplified schematic of the basic control of the 2KL less ALC and protection circuits.

The simplified schematic uses the same reference designators as the Icom schematic. The circuit shows normal operations available from the front and rear panel. It involves turning Q7 on or off which supplies the bias to the two amplifiers PA1 and PA2.

For Q7 to be on ( amplifier enabled ) requires Q5 to be on and Q4 to be off. Q4 off allows current through R54 to turn on Q5 and Q7

For Q7 to be off ( amplifier disabled ) requires Q5 to be off and Q4 to be on. Q4 on shorts the base of Q5 turning off Q5 and Q7.

In normal operation with the front panel “Linear” switch in the "off" position, there are two bias paths that turn on Q4. One path is via the "Linear" switch through R50 and R25 and the other via R52 and R53.

The “Send” line goes to the rear panel connector of the same name and to pin 1 of the accessory connector. Ordinarily grounding the “Send” line would turn off Q4 enabling the amplifier but as long as the “Linear” switch is in the off position, current from the switch through R50 and R25 keeps Q4 on preventing the “Send” line from turning Q4 off. The amplifier remains disabled regardless of the condition of the “Send” line.

If the "Linear" switch is moved to the "on" position, it turns on the front panel LED D11 and disconnects the bias path via R50 and R25. This allows grounding the "Send" line to turn off Q4 which enables the amplifier bias.

[HAMHOCK75]

The forward and reflected power of the SWR coupler is monitored by several of the protection circuits. It was found that the SWR coupler used is a widely known variation of the Bruene coupler. The 2KL operating manual never mentions the purpose of C54. It’s purpose is to calibrate the coupler as explained in this paper.

http://www.collinsradio.org/wp-content/uploads/2015/05/Understanding-the-Bruene-Coupler-Transmission-Line-Bold.pdf

To do the calibration, the 2KL was set up with a LP-100A power/swr meter monitoring the 2KL output which read 497 watts with a SWR of 1.07:1 at 14.2 MHz. Two voltmeters were used to monitor pins 3 ( reflected power ) and 2 ( forward power ) of J2 on the LPF assembly shown in the figure below. C54 was adjusted to minimize the voltage on pin 3. The measured voltage on pin 3 was about 0.8 VDC and on pin 2 about +5.18 VDC.



The coupling factor was calculated with the following assumptions. The the diode detectors are operating in the linear region and that the voltages measured into a voltmeter would be half into a 50 ohm termination. The forward power as measured on the LP-100A is 497 watts. The power calculated into a 50 ohm load on the forward power side would be P = ( V**2) /R or P = ( (5.18/2) * 0.707 ) ** 2 /50 = 0.067 watts. The coupling factor would be 10 log ( 0.067/497 ) = -38.7 dB.

Using the same idea, it can be calculated that the reflected power would be about 0.0016 watts. Based on the coupling factor determined above, that would indicate the reflected power is about 11.87 watts. This represents an SWR of 1.37:1 where the reflected power for a 1.07:1 SWR is about 0.6 watts.

I suspect the LP-100A coupler is designed and calibrated much more carefully than the 2KL coupler. Does anyone feel that this performance of the 2KL coupler is poor or is this typical of what one would expect from this design?

[VK6HP]

HH75,

I suspect your Icom coupler is about par for the course for a mass-produced and unoptimized unit.  Characterization is of course much easier in an external coupler in which the forward and reverse inputs are easily interchanged.  Coincidentally, I've been playing with "minimum couplers" as part of my homebrew LF/MF PA protection schemes and, having a PCB mounted unit, I've had some of the same characterization issues as you've struck; I'll make a couple of quick practical observations which might be useful.

I've found my units work best in terms of linearity and accuracy with Schottky power rectifiers (something like an SS24) and by keeping the Bruene RFC arrangement from the coupler secondary centre tap.  With my Class D/E amps I set the forward power indication in the usual way then use a couple of calibrated resistive mismatches (e.g. two 50 ohm loads in parallel) to optimize the SWR readings in the 1-2 region: the region I care about most in this application.  I use cross-needle meters, with the usual variable resistor multipliers.  Having pretty rugged HEXFET devices, I then set the forward power to about 40 W and just open-circuit the output, adjusting the PA reverse power trip to that point. (With a more conventional PA you'd likely vary the technique and levels a bit).

How well I do with the simplest couplers depends markedly on how careful I've been during construction, including secondary bifilar wire twisting and winding, and minimization of stray coupling.  Without doing any maths your pin 3 null voltage seems a bit high but I wonder if that's connected to some other node that might be influencing your dc minimum reading?

There's a world of optimization to be done on the coupler and diode operating points etc. but, in practice, I've declared the simple coupler "good enough" for what I'm using it for.  Alternatives like tandem couplers tend to be popular nowadays and, well implemented, they have advantages.  However, there are many sub-optimum implementations around, in which simple things like minimizing the shunt reactance burden on the main line (and the effect on the unit's own insertion match) are neglected.

73, Peter.

[HAMHOCK75]

Without doing any maths your pin 3 null voltage seems a bit high but I wonder if that's connected to some other node that might be influencing your dc minimum reading?

Connector J2 only has a +13.8 VDC input to the LPF assembly and the two outputs from the SWR coupler. I disconnected the mating connector to J2 and used a jumper to connect the +13.8 VDC. Then measured the forward and reflected outputs from the Bruene coupler without those outputs connected to anything else.

I now get a very nice null to 0.066 VDC reflected and 6.6 VDC forward. Without doing the math here, that is an SWR of 1.02:1.

Looks like it is time to find out where the noise is coming from that is limiting the lowest measured SWR to about 1.37:1 when it is really much better.

[VK6HP]

66 mV sounds more like it!  Good luck...

[W9IQ]

Another factor that often affects the accuracy of the Bruene style bridge is the location of the capacitive voltage divider in relationship to the current transformer. Since the accuracy of the bridge is dependent on the complex values of the sampled voltage and current, a frequency dependent phase error can be introduced by poor component location choices.

The resistor shunting the lower arm of the capacitive divider appears to be a compensator for strays in the circuit as this will alter the ratio of the sampled voltage as the frequency is varied. It would be interesting to calculate its effect over the HF range.

With that being said, I am sure there was no attempt to make the bridge a wide range, high accuracy device. It is simply fit for purpose.

- Glenn W9IQ

[LZ1HD]

HAMHOCK75, The reverce voltage is supplied to the Main Unit IC1A/pin2. However, at the same point, the voltage that controls the Input Power is supplied, it is overdrive protection. This same voltage is the so-called noise. However, you do not need to try to balance the bridge with 500 W, 100 W will be more than enough. Thus the Drive Power will interfere less. If you want to test how the Bruene coupler works, I recommend to disconect J2 on LPF, connect 22K resistors with RFL and FWD outputs to GND and control the voltages with two voltmeters. In these conditions you can achieve optimal balancing. Of course this must be done on 14Mhz.

Veselin LZ1HD