RCI 6900F TB: Reviews, ALC Mod, Tune-Up, PCB Adjustment Locations, Frequency And Clarifier Modification

The RCI 6900F TB is a fine-looking transceiver. There are two versions of the RCI-6900. First is the RCI-6900F HP. The HP stands for high power. This may confuse many operators, but the HP apparently first came with the Connex 3300HP. High power back then meant a dual final radio. The early export radios had single final output stages, and Connex used the HP to show the distinction between those radios and their higher-power version.

The other is the RCI-6900F TB, which is reviewed in this article. The TB stands for turbo. This designation was first used on the Galaxy Saturn Turbo base station, which was a 100-watt radio. Instead of having two different part numbers as they do with the 2950 and 2970, they chose this method of distinction.

This radio incorporates a main circuit of a newer design. It shares the front-end, mixer, and IF stages with the RCI 2950DX. Oh, yes, it even shares the problem related to the sideband crystal filter area of the board. This radio incorporates SMT, the surface mount technology type circuit board.

Review of the RCI 6900F TB 10-Meter Transceiver

As I’ve discussed in earlier issues, this technology is the wave of the future in electronics. This type of construction is far more reliable but more difficult to repair or rework. The advantages are many in using this type of circuit board. The components are much smaller which means more components will fit in a smaller area.

This advantage can be used to reduce the size of a product, increase the complexity of the circuitry in a given area, make the unit less congested, or all of the above.

In addition, although the components are still a little more expensive, manufacturing is automated reducing assembly cost.Initially I shied from this radio because earlier versions of this 12 band PLL design weren’t good in the sideband mode of operation.

Strong received signals were garbled and the transmission had a slight warble to it. In addition, there were reports from another radio dealer that in sideband mode, RCI-6900F TB would indicate a high level output with no audio applied. Looking at the internal RF meter, it looked as if there was a carrier on sideband.

This happened only on certain antennas. Earlier this year, a customer sent an earlier version of the RCI-6900F TB for repair of the carrier problem mentioned earlier. After analysis, I determined the 150-amplifier stage was going into oscillation. This occurred because there was no negative feedback on the output amplifier.

This was immediately solved by adding a 51W 1-watt resistor in series with a .01 mf capacitor from the base to the collector of the 2SC2290 transistors. The current RCI-6900F TB radios have this negative feedback installed. They use a 47W resistor in series with a .01 mf capacitor. See Photo for location of components.

Initial bench testing indicated Ranger also cured the PLL stability problem; this radio was solid as a rock drifting only 40 Hz from turn on to one hour of use. However, as mentioned earlier, the receiver has the same imaging problem on sideband as the RCI-2950DX tested in our September issue.

Testing the receiver on AM and FM concluded this radio performs better in those modes than many other 10-meter radios of the past and present.

Testing the sideband receiver indicated very high sensitivity, but low selectivity. Injecting a signal that read 30dB on the “S” meter, resulted in a clear reception of this signal 10KHz on either side of the channel with a reading of “S” 9 on the radio’s meter.

This signal stayed the same approximately 100KHz on either side of the channel and slowly decreased to a “S” 7 over 200KHz or 20 channels on either side of the channel. It’s important to note that the signal isn’t distorted like ordinary splash or bleed-over, it remains clear, as if it were on the same frequency blending in with other transmissions.

This may be why I’m hearing that nobody has complained, the end user may think the signal is on the same channel, because it blends with the other sideband traffic. Removing the filter from the circuit board revealed the same “S” 9 signal on the test channel as on the adjacent channels as well as displaying the same results as if the filter were still in place.

The good news is that the same fix works, as I expected, for the RCI-6900F TB as the RCI-2950DX. See the article RCI 2950DX Image Rejection Modification for the information needed to perform this modification. Please remember, you’re on your own.

If you’re not sure if you have the soldering equipment or skills to perform repairs or rework of SMT, don’t attempt it. Damaging the radio will surely void your warranty! CB World Informer can’t and will not be responsible for any actions individuals take using our information.

Testing the transmitter on the bench indicated an issue with the sideband ALC. At full power the first second or so of transmission only reached 10-Watts PEP, regardless of mic input or mic gain. It would then reach momentary peaks of 100-Watts with an average of 35-Watts PEP. After every loud

syllable the ALC was so tight the next two or three words were reduced to 10 to 35-Watts PEP.

This pumping action caused the transmitted sideband signal to sound sporadic and would create problems effectively communicating long range, defeating the reason for the extra power in the first place.

This occurred in two RCI-6900F TB radios tested. Don’t be disheartened, there is a fix in the RCI 6900F TB Tune-up And PCB Adj. Locations article.

Remember, when you buy one of these radios from Bob’s CB & Wireless, all this work is done before the radio leaves the shop.

Below is a table of non-tuned power readings, tuned up power readings, and the tuned up sideband readings after the ALC modification. The increase in power is designated in red and the reduction in power is designated in green.

Radio Tested Out Of The Box

Radio Tested After Tune-up

Radio Tested After Tune-up & Modification

Packed with features like an automatic calibrating SWR meter, 6-digit frequency counter, fine and coarse clarifier controls, roger beep, preset echo ON/OFF, adjustable talkback, +10KHz switch, and a power plant capable of 150-Watts PEP, this radio is a compact powerhouse!

The +10KHz switch is used to pick up those frequencies skipped, as discussed in last month’s General Lee Review. The coarse clarifier moves both the transmitter and receiver frequency more than ±5KHz, while the fine control makes tuning sideband signals very easy.

Using the 6-digit frequency counter makes finding the center slot a snap. See the front panel control locations below.

RCI-6900F TB Front Panel Controls

                         Frequency Pool (Out of the box)

Although I pointed out issues that Ranger should look into on this radio, I very much like this one. Once the modifications are out of the way, this is one fine radio. The AM has a great deal of punch, just what the guys are looking for in this radio. The AM, FM, and sideband reception are the same as the RCI 2950DX.

The modified transmitter pushes a clean 150-Watts PEP, and the smooth average is about 120-Watts. I’d say it’s the first band-selected type of radio that has the performance of HF radios 2 to 3 times the cost. This radio is definitely for the guys who like going up or down with one click.

For Amateur operators, this radio covers most of the 10-meter band once converted but stops just before the end of the FM phone portion. Although it can go anywhere in-between, using the +10KHz switch and clarifier is a little cumbersome to get where you want to go.

If you’re the type of radio operator who doesn’t like driven radios with memories or find the buttons on those radios too small to hit while you’re bouncing down the road in your 18-wheeler, this radio has the power, modulation, and receiver that you’ve been waiting for.

RCI 6900F TB ALC Mod, Tune-Up, And PCB Adjustment Locations

The ALC modification requires the removal of surface mount parts and the addition of conventional through-hole type parts. When removing these components, take extra care not to overheat the circuit board. The traces will lift quite easily.

When installing standard components, due to their larger size, it’s best to solder them to the trace where another component is already soldered.

This will be a stronger connection as these larger components will vibrate and pull the traces up in time. If you’re unsure about your capabilities, don’t attempt this modification. Take the mod to a local technician or send it to Bob’s CB & Wireless.

RCI-6900F TB Sideband ALC Modification

• Change R259 from 470 Ohm to 10K (See Figure 1)
• Change R271 from 1K to 2.2K (See Figure 2)
• Add two 1N4148 diodes in series across the R217 band side to ground. (See Figure 2)

The following adjustments require the front panel RF Power Control to be set to the fully clockwise position.

To adjust the SSB power, set VR18 SSB Limit to the maximum and adjust VR14 up to 150-Watts PEP. This will produce a clean SSB signal from minimum power to maximum power. For AM, Set VR15 to 50 to 70-Watts and adjust VR17 for a modulation swing of 150-Watts peak.

Remember; the front panel control will allow the RF carrier output to be reduced at will. If you don’t want many swings at low power, unfortunately, the modulation adjustment will have to be reduced, and a 150-Watt peak at high power won’t be possible.

RCI 6900F TB Photo

The RCI-6900F TB Front Angle View

The RCI-6900F TB Front Panel With Oversize Heatsink Fins

The RCI-6900F TB Rear Panel

The RCI-6900F TB Bottom Cover Off With View Of Power Amp Shield

The RCI-6900F TB Power Amplifier With Negative Feedback Components Labeled

The RCI-6900F TB Echo Board With Shield Removed And Controls Labeled

Expanding The Coverage Of The RCI-6900F

1. Remove the 100 ohm resistor on the circuit side of the PC board.

2. Turn the radio over and move the connector with three wires from J5 to J29.The HI/LO switch becomes a frequency HI/LO control, doubling the bands from 6 to 12.

Figure 1

Clarifier Modification (Refer To Figure 2)

1. Carefully remove diode D63.

2. Cut the black wire from the connector on J10.

3. Solder this wire to the 8-volt circuit on the PC board.Now the fine clarifier will track and change the transmitter and receiver frequency.

Figure 2

Expanded Frequency Pool