PRESIDENT LINCOLN COOKBOOK

2 Two Stage Power Level

This section details modifications to add a two-stage power level switch to the Uniden HR2510 and HR2600 radios, allowing operators to adjust power for DXing and QRP operations.

2.1 F/QRO and QRP/QRO Versions

The modification involves adding a switch to insert resistors in series with internal potentiometers to control power output. F/QRO means Factory power levels on low, QRO on high. QRP/QRO is similar but with much lower QRP levels for portable use or driving linear amplifiers.

For the F/QRO version, use 2.2k/3.3k resistors. For the QRP/QRO version, use 5.6k resistors. The switch has 'A' and 'B' poles.

The procedure involves connecting to a 13.8V DC power supply, using a watt meter and dummy load. Initial tuning of carrier and ALC levels is required using VR107/VR8 and VR104/VR5 respectively. The microprocessor PCB needs to be carefully moved to access solder points on the main PCB for installing the switch wiring. Two methods for wiring the 'B' portion are described: routing wires to appropriate pads or drilling holes for a more professional installation.

Diagram for Two-Stage Power Level

A schematic diagram illustrates the two-stage power level switch. It shows a DPDT switch with poles labeled 'A' and 'B'. Pole 'A' connects to a 2.2K resistor and a diode (D159/D57) for AM/FM carrier and SSB/CW power control. Pole 'B' connects to 3.3K and 5.6K resistors (depending on version) and a variable resistor (VR107/VR8) for SSB/CW power control. The diagram also shows connections to ground and a cut ground trace.

SSB Modification: Isolate VR104 (VR5 in HR2600) from ground. Connect 'B1' wire to PCB ground and 'B2' wiring to the isolated pad of VR104 (VR5). Mic Gain can further reduce PEP.

Carrier (AM/FM) Modification: Lift the cathode of D159 (D57 in HR2600) and connect wire 'A2' to it, covering the diode and connection with heat shrink tubing. Connect wire 'A3' to the hole vacated by the diode at the variable resistor. The President Lincoln has an external carrier control, so only the 'B' portion of the switch is needed for it.

Table of parts regarding Two-Stage Power Level

2.4 Variable Power Controls

These controls can be paralleled or replaced with outboard controls for total power management. Using the two-stage control is recommended when using an amplifier to prevent accidental high power settings.

3 The Mystery of the 9-Pin Molex Plug

This section questions the use of the 9-pin plug on the rear heat sink for internal/external speakers, CW key, and PA Speaker on HR2510/HR2600/Lincoln radios. It suggests the plug could be repurposed for accessories like amplifier keying, transverter inputs/outputs, or external monitoring points (S/RF meter, AGC metering).

4 Better Noise Blanker Performance

This modification involves replacing 1N60 diodes with better-performing Schottky barrier types (e.g., ECG584). In the HTX-100, these are D1 and D2. In the HR2510/HR2600/Lincoln, they are D201 and D202 on sub-board PB117AA. Peaking the noise blanker coil (L1 in HTX-100, L203 in HR2510/HR2600/Lincoln) at the noise frequency is also suggested.

5 "OOPS!" Found in Manuals

This section highlights errors found in other manuals, specifically the HTX-100 manual regarding transmitter alignment procedures (VR11 vs. VR12 for bias adjustment) and the HR2600 manual concerning chip pin-outs (TDA1905 vs. PLL0305A).

6 A 12 Meter Uniden Radio?

Details a modification for HR2510 radios to operate on 12 meters (24.475 to 28.475 MHz) by changing the 22.0 MHz crystal (X302) on the synthesizer board to a 10.240 MHz crystal. This modification does not affect the frequency readout, requiring a channel chart. The HR2600 modification for extended range is noted as less effective, yielding approximately 26.475 to 28.175 MHz, suggesting a 6 MHz crystal for this range. A diode-switching board is proposed for switching between crystals.

7 Audio Capacitor Update

Recommends replacing sub-standard electrolytic capacitors in earlier versions of Uniden boards (HR2510/HR2600/Lincoln, HTX-100) that have caused failures. The original capacitors are often 10-volt rated and should be replaced with 16-volt or preferably 25-35 volt rated capacitors. Specific capacitor numbers (C95, C97, C130 for HR2510/HR2600; C102, C103 for HTX-100) are mentioned. Microfarad values should remain the same.

8 Better AM Receive Audio

Suggests replacing AM detector diodes (D111 and D112) with better Schottky barrier diodes (e.g., ECG583) for improved AM receive audio. This is noted as not applicable to the HTX-100 due to its lack of AM reception.

9 A Simple Power Boost

Suggests paralleling capacitor C127 with a 680 pf capacitor for the HR2510/HR2600, or C131 with a 330 pf capacitor for the HTX-100, to realize several more watts of output.

10 A Simple RIT Modification

Provides a quick modification for variable TX/RX control (RIT). Steps include removing D150, routing an orange wire from the 4-wire molex plug to the +7 volt pin of IC311, and centering the RIT control while adjusting L315 on the microprocessor board.

11 A Different Light On Things

Offers a cosmetic modification to change the meter/frequency display lighting from orange to another color (e.g., red for military use, light blue) by replacing the wheat bulb and hood.

12 A Simple Talk-Back Removal

Suggests removing capacitor C137 (10v 22uf) and resistor R199 (1k ohm) from the base of transistor Q117 to eliminate feedback problems, which may cause a slight "POP" when un-keying.

13 Quickie Transmitter Tune-Up

Provides a procedure for tuning the transmitter at band edges for Uniden/Realistic radios. It involves tuning forward coil Lxx for peak output, then peaking the center coil of FTxx for center band, the rear coil for low end, and the forward coil for the high end of the band.

Associated components mentioned:

• FT4: HR2600
• FT104: HR2510/Lincoln
• FT3: HTX-100
• L25: HR2600
• L111: HR2510/Lincoln
• L26: HTX-100

14 Mic Wiring

Details the 5-pin plug scheme for the HR2510/HR2600 microphones (Audio, Ground, Transmitt, Scan Up, Scan Down). Notes that pins 4 and 5 (Scan Up/Down) can be grounded for function. It also mentions using a DPDT switch for Up/Down features and refers to an article for 100 Hz tuning modification.

For the HTX-100, it describes the more common 8-pin plug scheme (Audio, Shield/Ground, Scan Down, Scan Up, No Connection, No Connection, Ground, No Connection).

15 The Power Mod Revisited

Discusses the "Beef Up/Power Mod" from a "73 Amateur Radio" article, noting varied success and a retraction. It explains that the mod, when combined with power mics, can cure overdrive conditions. Earlier models (serial numbers 830xxx) showed power increases, while later models (950zzz) seemed to have no increase, possibly due to a power limiting circuit. Replacing the pre-driver and final transistor is suggested to fix overdrive and gain power.

* Pinouts are exactly opposite: 2SC2086D=BCE, ECG/NTE340=ECB

** The external carrier level control on the Lincoln replaces the internal pot VR107. The AM/FM carrier and CW level can be adjusted with VR103.

16 AGC Test Tap

Describes how to add an AGC (Automatic Gain Control) test tap using an RCA jack and a 10K resistor. This allows measurement of AGC voltages for antenna tuning and maximizing efficiency. The tap is connected to the anode end of specific diodes (D116 for HR2510/Lincoln, D18 for HR2600, D5 for HTX-100).

17 Transverter Topics

Details a modification for the Uniden HR2600 to interface with a Microwave Modules MMT 144/28 2-meter linear transverter. The modification involves removing PB-100 (a circuit board) and soldering a jumper between TP2 and TP4 to supply +VCC to the driver stage while removing it from the final power amplifier. This provides sufficient driver energy to excite the transverter. A suggestion is made to use a switch for "Standard" vs. "Transverter" settings.

18 Miscellaneous Mods

18.1 Increase Receive Audio

Add a 4.7 µF capacitor in parallel to R152 (a 560 ohm resistor).

18.2 Mute Circuit Improvement

Remove C137 and R199 to improve muting.

18.3 CW Click

Caused by improper attack time in the power control circuit. Component changes are recommended:

• Original R21 (1.2K) replaced with 560 Ohm
• Original R119 (10K) replaced with 5.6K
• Original VR107 (47K) replaced with 22K

Note: After this modification, re-adjust AM/FM TX power to 10 watts.

18.4 Transmission of Burst Signal on Stand-By (TX to RX)

A circuit diagram shows an additional mute circuit for the pre-driver section. The text states that adding this mute circuit will stop all carrier transmission except during the keydown period.

19 Block Diagram of PLL Circuit

A block diagram illustrates the Phase-Locked Loop (PLL) circuit. It shows signal paths from a 5kHz reference, a 10.24MHz oscillator (Q308), a 22MHz oscillator (Q304), a DIA converter (IC307), a loop filter (IC306-1/2), VCOs (Q302, Q303, Q306), mixers (IC305, IC304), and low-pass filters (LPF). The diagram details frequencies and component identifiers (IC, Q) involved in frequency synthesis and control, including an RIT (Receiver Incremental Tuning) function.

20 Troubleshooting Charts (HR2510)

These charts provide diagnostic steps for common issues.

20.1 Transmitter Section

Covers issues like "No Transmission" and lists checks for PTT Switch, Microphone, Microphone Jack, Microprocessor circuit, specific pins and voltages (Q136, Q125, Q127, IC105, IC106, IC104), voltage/frequency at TP5, antenna, antenna wire, voltage/frequency of Q106 emitter, and voltages of Q24, Q25, Q23. It uses "NG" for "No Good" and suggests replacing defective parts.

20.2 Receiver Section

Addresses "No reception" and includes checks for speaker/wire connections, voltages at IC103 pins 7 and 1, voltages of Q127 and Q136, and operation of the SQ control. It also checks voltage levels and frequencies at TP3 and suggests replacing defective parts or adjusting controls.

20.3 PLL Section

Troubleshooting steps for the PLL circuit, checking LCD display, frequency at Q308 emitter, voltages at TP301, TP302, TP303, TP305, TP307, and frequencies related to various ICs and transistors (IC301, IC302, IC303, IC304, IC305, Q301, Q302, Q303, Q304, Q305, Q306, Q308). It also checks the connection of J311 and suggests replacing defective parts.

20.4 Microprocessor Section

Troubleshooting for the microprocessor section, checking LCD display, clock signals at IC502 pins 44/45, waveforms at IC502 pins 1/52 and IC502 pins 6/13, operation of S901, S605/S612, and PTT switch. It also checks voltages of IC310, IC314, IC315, Q315, Q316, Q317, and S603. It notes that Mute is IC315 pin 63 and Beep is IC315 pin 33.