Video Link: The Parts That Make Up a Tube Radio

We start by providing a comprehensive breakdown of a 1950s/60s German tube radio (Nordmende Rigoletto), transitioning from complex schematics to the physical components on the chassis.

1. Schematic Mastery & Simplification

• Importance of the Service Manual: Discussion on the necessity of a high-quality schematic to avoid costly mistakes, such as blowing rare output transformers.

• The "Layering" Technique: Demonstration of using a drawing program to hide "clutter" (model numbers, pinout values, and complex switching) to clearly visualize the signal path.

2. Signal Path & Functional Blocks

• AM Front End & Mixer: Explanation of how the AM signal is pre-selected and mixed with a local oscillator frequency to create a manageable 460 kHz Intermediate Frequency (IF).

• FM Front End: Overview of the FM block (often housed in a shielded metal box), which uses an ECC85 tube to amplify and mix signals to a 10.7 MHz IF.

• IF Amplification: Description of the IF transformer "cans" and the EF89 tube, which together filter and boost the signal while ignoring interference.

• Detection & Audio Pre-Amp: Analysis of the EABC80 triple-diode/triode tube, which decodes the radio signal into audio and provides the first stage of amplification.

• The Power Stage: Final signal flow through the EL84 power tube and the output transformer, which drives the speakers and electrostatic tweeters.

3. Physical Component Identification

• The Chassis Tour: Direct correlation between symbols on the schematic and physical parts on the radio, including the tuning condenser and various transformer lugs.

• Tube Functions: Identification of standard tube types found in mid-century European sets and their specific roles in the circuit.

4. Power Supply & Safety

• Safety Warning: Essential precautions regarding high-voltage "anti-zapping" measures and the risks involved in tube radio restoration.

• The "Heart" of the Radio: Justification for restoring the power supply first. This includes checking the primary transformer windings, the selenium bridge rectifier (converting AC to DC), and the multi-section filter capacitor can.

• Heater Circuit: Brief explanation of the 6.3V AC winding used to power the tube filaments and dial lamps.

Conclusion: By isolating these specific sections, the intimidation of a "bird's nest" of wiring is removed, allowing for a logical, step-by-step restoration.

Video Link: Checking the Power Supply

This video covers the initial hands-on steps of restoring a tube radio's power supply, focusing on safety, troubleshooting common points of failure, and modernizing the rectification circuit.

1. Primary Circuit Troubleshooting

The process begins with isolating the power supply on the schematic to simplify the circuit. An initial test of the power plug often reveals an "open circuit," which can be mistakenly attributed to a dead transformer. In this demonstration, the issue is traced back to heavily oxidized fuse contacts and a dirty power switch. Using contact cleaner to restore these connections allows for a proper continuity reading, confirming the primary winding of the transformer is intact.

2. Safe Transformer Testing

To verify the transformer without applying dangerous mains voltage, a low-voltage AC signal is injected into the power plug using a signal generator. By measuring the resulting voltages on the secondary and heater windings, the transformer's step-up and step-down ratios are confirmed. This provides a safe way to ensure the "heart" of the radio is healthy before proceeding with the restoration.

3. Upgrading the Rectifier

A major portion of the video focuses on the replacement of the original selenium bridge rectifier. Selenium rectifiers are notorious for high internal resistance and heat generation, which worsens as they age.

• The Solution: A modern silicon diode bridge is used as a replacement.

• The Voltage Drop: Because modern silicon diodes are more efficient, they produce a much higher output voltage than the original components.

• Ohm's Law in Practice: The video explains how to calculate the value of a series resistor (typically around 300 ohms) to mimic the original voltage drop, ensuring the radio's delicate tubes aren't overdriven by excessive voltage.

4. Installation and Safety

The replacement is performed using a custom PCB designed to fit the original mounting holes on the chassis. Nylon spacers are used to prevent high-voltage shorts against the metal frame. The video concludes with the secondary leads successfully attached to the new board, emphasizing that while these steps are straightforward, the high DC voltages involved require constant caution.

Final Takeaway: By cleaning old contacts and replacing the aging rectifier with a modern, resistor-tuned silicon circuit, the power supply is made stable and ready for the next phase of restoration.

Video Link: How to Check the B+ Safely

This guide covers the finalization of the power supply restoration and the critical "cold" checks required to ensure the high-voltage lines are safe before powering the radio.

1. Capacitor Replacement & Restuffing

• The Role of Filter Capacitors: Analysis of how electrolytic capacitors smooth rectified DC to eliminate audible hum.

• The "Restuffing" Process: Demonstration of opening the original aluminum can, removing the dried-out internal electrolyte, and installing modern, compact Nichicon capacitors inside. This technique preserves the radio’s original aesthetic while ensuring reliability.

• Grounding Reliability: Implementation of a dedicated ground wire for the new capacitors to prevent the common issue of intermittent connections caused by corrosion on the chassis-mounted can.

2. Alternative Recapping Methods

• Under-Chassis Mounting: Overview of a simpler alternative where new capacitors are mounted to tag strips underneath the chassis, leaving the original can disconnected but in place for visual authenticity.

3. "Cold" Checking the B+ Lines

• Resistance Testing Strategy: Explanation of using a multimeter to trace the high-voltage path throughout the entire radio while the power is off.

• Component Verification:

  • Output Transformer: Measuring the primary windings to confirm the power tube is receiving voltage.

  • Resistor Networks: Checking the values of various voltage-dropping resistors that supply the pre-amplifier and Magic Eye indicator.

  • IF Transformers: Verification that the internal primary coils are intact, ensuring DC voltage reaches the intermediate frequency stages.

4. Functional Switching Logic

• High-Voltage Routing: Analysis of how the radio’s band switches direct power only to the active sections (FM or AM). This ensures that unused tubes are effectively "switched off" during operation.

Final Takeaway: Verification of the entire high-voltage circuit through resistance checks provides a safe way to identify open resistors or broken coils without the risk of "zapping" components or the restorer.

Video Link: How To Check the Power Amp Stage 

In part four of the restoration series, the focus shifts to the audio section. The restorer’s philosophy is to work backward from the power supply to the audio amplifier, ensuring the radio can actually produce sound before tackling the RF and tuning sections.

1. Audio Section Components

• The Key Tubes: The audio stage relies primarily on two tubes:

  • EL84: The power pentode responsible for the final amplification stage.

  • EABC80: A multi-purpose tube; while it contains diodes for radio detection, its triode section is used here as the audio pre-amplifier.

• Basic Signal Flow: Audio travels from the selector (FM, AM, or Pickup) through the volume control to the preamp (EABC80), then through tone-shaping circuitry to the power amp (EL84), and finally to the output transformer and speakers.

2. Technical Theory & "Tone Shaping"

• Tone Shaping: This radio features sophisticated tone-shaping elements, including bass and treble controls, preset buttons (Jazz, Orchestra, etc.), and a negative feedback loop from the speaker back to the preamp to optimize sound quality.

• Understanding Bias: A deep dive into "cathode bias." By using a resistor and capacitor on the cathode, the tube creates its own negative grid-to-cathode voltage. This "squeezes" the current flow (like a tap), preventing the tube from running wide open and burning out.

• The Critical Coupling Capacitor: This capacitor blocks DC voltage from the preamp's anode while allowing the AC audio signal to pass to the power tube's grid. If this component leaks DC, it can cause the power tube to "run away" and destroy the output transformer.

3. Bench Work & Component Testing

• Cathode Circuit: Testing the 180-ohm cathode resistor (found to be perfect) and replacing the 100µF bypass capacitor, which had drifted significantly in value.

• Grid Circuit: Tracing the signal path through the grid leak and grid stopper resistors, as well as the bass control potentiometer.

• Leakage Testing: Using a dedicated high-voltage tester to check the old coupling capacitor for DC leakage. Although this specific film capacitor was still in excellent condition with zero leakage at 330V, it was replaced as a standard safety precaution.

Final Takeaway: By understanding and verifying the DC bias conditions and the integrity of the coupling stages, the amplifier is made safe for its first power-up.

Video Link: Testing the Output Stage & Electrostatic Tweeters

In part five, the restorer explains the operation of the electrostatic tweeters, simulates tone control circuits, and performs a live "power-on" test of the audio power amplifier stage.

1. Electrostatic Tweeters & Switching Logic

• How They Work: Unlike standard speakers, electrostatic tweeters use two plates with a high DC voltage between them. An audio signal is superimposed on this DC, causing the plates to vibrate.

• High-Pass Filtering: A small 2000pF capacitor ensures only high frequencies reach these tweeters.

• Switching Logic: The signal to the tweeters is controlled by the FM and "Base" (Bass) buttons. Through circuit tracing, the restorer finds that selecting Bass or FM changes the resistance in the tweeter circuit, effectively altering the treble output to make the overall sound more "bass-heavy" or optimized for FM.

2. Tone Control Simulation (LT Spice)

• Bass Control: Simulation shows that the bass potentiometer works by progressively cutting low frequencies as it is turned. Interestingly, in many of these vintage radios, the control works in "reverse"—turning it counter-clockwise provides more bass.

• Treble Control: This acts as a "treble bleed." A capacitor allows high frequencies to escape to ground; the treble pot acts as a variable blockage. The more resistance added (clockwise), the more treble is forced through to the output rather than escaping.

3. Live Power-On Test

• The "Dim Bulb Limiter": To prevent catastrophic failure, the radio is powered through a light bulb. If there is a short, the bulb glows brightly, limiting the current to the radio.

• Signal Injection: Without the pre-amp tube installed, the restorer injects an 800Hz audio signal directly into the power tube stage through a DC blocking capacitor.

• Results: * The speaker produces a loud, clean tone.

  • Oscilloscope monitoring shows a healthy sine wave, reaching about 3.3V RMS into an 8-ohm load (roughly 1.3 Watts) before clipping.

  • Voltage checks confirm the power supply (rectifier and filter caps) is providing stable high voltage.

Final Takeaway: This test confirms that the fundamental "engine" of the radio—the power supply and the power amplifier—is fully operational. The radio is now effectively a working mono tube amplifier.

Video Link: Preamp, Tone Shaping and Detail

In part six, the restoration focuses on the preamplification stage, rebuilding a unique "shielded" component, and explaining the complex negative feedback system used to shape the radio's tone.

1. The Preamp Tube (EABC80)

• Multi-Purpose Design: The radio uses an EABC80, which contains a triode (used for audio preamplification) and three diodes (used for detection and FM).

• Grid Leak Bias: The triode doesn't use a cathode resistor for biasing. Instead, it uses a 10 megaohm "grid leak" resistor. This massive resistance creates a small negative voltage on the grid from stray electrons, providing the necessary bias for amplification.

2. Rebuilding the "Shielded" Capacitor-Resistor

• The Component: The restorer removes a failing component (C171/R172) that combines a 10nF capacitor and a 10MΩ resistor within a metal shield.

• The Rebuild: Since the original is leaky, he recreates it using a modern film capacitor and a resistor, wrapped in copper tape (to act as the shield) and finished with green heat shrink to match the original aesthetic. [21:25]

3. Audio Path & Switching

• Signal Routing: The audio path is traced through the FM and Phono (pickup) switches.

• "Tag Points": A clever trick of vintage manufacturing is revealed: Pin 1 of the power tube (EL84) is used as a "solder tag" or dummy terminal for connecting wires, even though it has no internal connection to the tube itself. This often confuses restorers who assume it's part of the tube's circuit.

4. Negative Feedback & Tone Shaping

• Phase Inversion: By comparing the input and output on an oscilloscope, the restorer shows that the speaker signal is 180° out of phase with the input.

• Feedback Loop: Part of this inverted signal is sent back to the bottom of the volume pot. This "subtracts" from the input signal, reducing certain frequencies.

• Intentional Distortion: Unlike modern "Hi-Fi" amps that aim for perfect transparency, these radios use frequency-selective feedback to intentionally distort the signal in a way that sounds "rich" or "warm" to the human ear. This shaping is volume-dependent, meaning the tone profile changes as the user turns the volume up or down.

Next Steps: With the preamp and feedback circuits traced and partially rebuilt, the radio is nearing a state where it can process signals from its own internal AM and FM tuners.

Video Link: What do those Tone Presets really look like?

In part seven, the restoration moves to the front panel's tone-shaping selector assembly and explores the "psychological loudness" circuitry designed by German engineers to optimize the sound for human hearing.

1. The Tone Selector Assembly

• Mechanical Restoration: The restorer cleans the mechanical push-button assembly (Bass, Speech, Orchestra, Solo, Jazz). He uses an unorthodox but effective method: an airbrush compressor filled with alcohol to wash away decades of grime, followed by natural bristle brushes and cotton swabs.

• Component Testing: He verifies the resistors and switches within the "umbilical cord" (the wiring harness) against the schematic.

  • Solo Button: Measures exactly 10kΩ as expected.

  • Bass Switch: Confirmed to open and close correctly.

  • Jazz Switch: Verified to short the necessary capacitor into the circuit.

2. Psychological Loudness (The Volume Pot Taps)

• The Concept: At lower volumes, the human ear is less sensitive to bass and treble. To compensate, this radio uses a volume potentiometer with multiple "taps."

• The Circuit: A complex network of capacitors (including an 80pF "presence" capacitor) and resistors are hanging off these taps. As you turn the volume down, these components automatically boost the bass and treble relative to the midrange, preventing the radio from sounding "thin" or "tinny" at low levels.

3. Frequency Response Analysis

Using a PC-based spectrum analyzer (Visual Analyzer) and a custom scope buffer, the restorer visualizes the effects of the tone controls:

• Speech Mode: Clearly cuts off frequencies below 300Hz to eliminate "boominess," making voices easier to understand.

• Bass & Treble: While the analyzer shows subtle changes (about 3-6dB shifts), the restorer notes that the auditory difference is much more pronounced when listening to the actual speakers in the wooden cabinet.

• Volume-Dependent Curves: The most dramatic visual change occurs when adjusting the volume. Dropping the volume from 100% to 70% shows the midrange being "carved out" while the bass and treble remain relatively high—confirming the "loudness" circuit is working.

Current Status: The entire audio section, including the tone-shaping presets and loudness controls, is now fully restored and verified.

Video Link: Superheterodyne Theory, Oscillator Sniffing & Troubleshooting

In Part 8, the restoration moves into the AM radio section. The restorer begins by installing the missing IF amplifier (EF89) and mixer/oscillator (ECH81) tubes to test for reception. Initial tests reveal that while Long Wave (LW) and Short Wave (SW) are receiving signals, Medium Wave (MW) is completely silent, leading to a deep dive into how these signals are processed.

Superheterodyne Receiver Theory

The video provides a simplified breakdown of how a superheterodyne receiver works. It explains how a signal from the antenna is mixed with a local oscillator frequency to create a constant "Intermediate Frequency" (IF) of 460 kHz. This allows the radio to sharpen and amplify the signal consistently regardless of which station or band you are tuned to.

The "Sniffer" Coil Technique

To diagnose why Medium Wave isn't working, the restorer demonstrates a clever "hacker" trick: creating a "sniffer" coil. By winding solid core wire around a tube and connecting it to an oscilloscope, he creates a non-contact probe that can detect the magnetic field of the local oscillator. This confirms that the oscillator is indeed running on LW and SW, but failing on MW.

Solving the MW Mystery

The troubleshooting reveals that the lack of Medium Wave wasn't due to a broken component or a dead coil, but rather oxidized switch contacts. After some manipulation and cleaning of the complex switch bank, the MW oscillator springs back to life. The video wraps up with a look at the few remaining paper capacitors in the AM section and a preview of the upcoming IF and RF alignment process.

Video Link: Do we have FM, and how does it work?

Part 9 focuses on the FM section—the restorer’s favorite part of any vintage radio because of the superior sound quality. After cleaning the pins and socket for the ECC85 (the dedicated FM front-end tube), the radio is powered up via a dim bulb tester. Despite a simple wire antenna, the radio successfully receives FM signals across the entire band, proving that the previous restoration work on the shared signal path and power supply has already paid off. 

Simplified FM Schematic Analysis

The video uses a simplified schematic to show how the FM signal is processed. When the FM (UKW) button is pressed, it activates several internal switches that isolate the FM block and reroute the B+ power. 

• B+ Routing: Power is diverted to the FM metal block (the "tuner") while being removed from the AM-specific sections, effectively "turning off" the parts of the radio we aren't using.

• Signal Path: The FM intermediate frequency is 10.7 MHz. At this high frequency, the 460 kHz AM transformer coils act like short circuits, allowing the FM signal to pass through the same tubes (ECH81 and EF89) used for AM, but only as a simple amplifier. 

The FM Front End (ECC85)

The ECC85 dual-triode tube acts as both an RF amplifier and a mixer-oscillator. It amplifies the incoming signal from the antenna and mixes it with a local oscillator frequency (tuned to 10.7 MHz above the station frequency) to produce the 10.7 MHz IF signal.  

The Ratio Detector

The "magic" happens at the final stage using the EABC80 tube. This section uses a Ratio Detector (two diodes) to extract the audio from the frequency-modulated 10.7 MHz carrier.  

• Discriminated Capacitor: The restorer identifies the only component unique to the FM section that typically needs replacing: a small electrolytic "discriminator" capacitor (usually around 4–5µF). This capacitor stabilizes a negative DC voltage proportional to the signal strength, which is also used to drive the "Magic Eye" tuning indicator.  

FM Alignment Preview

A quick demonstration shows how misaligning the IF transformers causes the signal to fade. The restorer explains that while the first IF stages are tuned for maximum signal strength (measured as the highest negative voltage at the discriminator cap), the final ratio detector stage must be balanced for the best audio quality (minimum distortion).

Video Link: The all-important IF alignment of the AM

Part 10 of the Back to Basics series focuses on the AM Intermediate Frequency (IF) alignment. This process ensures the radio has peak sensitivity (the ability to pick up weak signals) and selectivity (the ability to distinguish between closely packed stations). For this 1959 Grundig, the specific IF is 460 kHz. 

Theory of Selectivity vs. Sensitivity

The restorer explains that while we want a sharp "bell curve" for selectivity to block adjacent stations, if the curve is toonarrow, the audio quality suffers because the sidebands (which carry the actual music and voice) get cut off. A typical AM signal needs about an 8 kHz bandwidth to sound "decent." 

Alignment Methods

The video demonstrates three ways to align the IF transformers (the top plugs on the IF cans in this model): 

1. By Ear: Listening to a weak station and adjusting the transformers for the loudest, clearest sound.

2. Signal Generator & Voltmeter: Injecting a 460 kHz signal (modulated with a 1 kHz tone) into the grid of the mixer tube (ECH81) and measuring the AC voltage at the speaker for a maximum peak.

3. The "Visual" Method (Sweep Generator/Wobbulator): Using a sweep generator to display the actual bell curve on an oscilloscope. This allows you to see the symmetry of the filter and ensure it is centered perfectly at 460 kHz. 

Key Technical Steps

• AVC/AGC Considerations: When using a signal generator, the signal must be kept as weak as possible. If the signal is too "hot," the radio's Automatic Gain Control (AGC) will kick in and flatten the response, making it impossible to find the true peak.

• Capacitive Coupling: The signal generator should be connected through a small capacitor to prevent the DC voltages in the radio from damaging the equipment or throwing off the tube bias. 

The Result

By the end of the process, the restorer achieves a perfectly symmetrical bell curve on the scope, indicating that the signal path is now optimally tuned for maximum performance. 

Video Link: How tough can the FM IF alignment be?

Part 11 covers the FM Intermediate Frequency (IF) alignment. While often seen as complex, the restorer demonstrates that it is straightforward if you have the right tools and understand the signal path. The goal is to align the radio to its standard FM IF of 10.7 MHz. 

Signal Injection Technique

A unique challenge with FM is getting the signal into the shielded front-end block. The restorer uses a "paper and foil" sleeve—a simple DIY tool made of aluminum foil wrapped around a paper tube—which is slipped over the ECC85 tube. This capacitively couples the 10.7 MHz signal from the generator into the radio's mixer stage without needing to open the metal enclosure. 

Alignment Steps

1. Peaking the DC Voltage: The restorer connects a multimeter across the ratio detector's discriminator capacitor. He adjusts the first four IF transformer cores (two on the front-end block and two in the first IF can) to achieve the maximum negative DC voltage. 

2. The "Zero" Balance (AM Rejection): To align the final stage of the ratio detector, he switches the signal generator to AM modulation. A ratio detector is designed to reject AM (amplitude jumps) and only hear FM. He adjusts the final core until the 1 kHz tone coming from the speakers is at its minimum (null point). This ensures the detector is perfectly balanced. 

Alternative Visual & Audio Methods

• Sweep Generator/Oscilloscope: The restorer attempts to "stagger-tune" the transformers to create a flat-topped "double hump" response curve on the scope for better bandwidth, though he notes this specific radio is stubborn and maintains a more traditional bell shape. 

• Sine Wave Monitoring: Another method involves monitoring the speaker output on an oscilloscope and adjusting the cores for the cleanest, highest-amplitude sine wave. 

The Result

After alignment, the radio is tested with a standard antenna and is found to be sounding "amazing" with clear reception across the FM band. This sets the stage for the final RF alignment (tuning the dial to the stations) in the next episode. 

Video Link: The 'Why and How' of an RF alignment

Part 12 focuses on the Radio Frequency (RF) alignment for the AM bands (Long Wave, Medium Wave, and Short Wave). This process ensures that the radio dial accurately reflects the stations being received and that the antenna circuit is tuned for maximum sensitivity. 

The Theory: Tracking and the Local Oscillator

The restorer explains that an AM radio doesn't just tune to a station; it uses a Local Oscillator to create a signal exactly 460 kHz (the Intermediate Frequency or IF) above the station's frequency. 

• The Problem: As you move the dial across the frequency band, the relationship between the antenna tuning and the oscillator tuning must stay consistent. This is called tracking. 

• The Fix: You adjust the inductors (coils) at the low end of the dial and the trimmer capacitors at the high end of the dial. Because these adjustments affect each other, it is an iterative process of "rinsing and repeating." 

The Alignment Process

1. Mechanical Zeroing: Before starting, the dial pointer is physically aligned to the end-of-scale markers on the glass. 

2. Medium Wave (MW): * Set to 555 kHz: Adjust oscillator coil A and antenna coil C for maximum output. 

   • Set to 1480 kHz: Adjust oscillator trimmer B and antenna trimmer D for maximum output. 

3. Long Wave (LW): * Set to 210 kHz: Adjust oscillator coil F. 

   • Sensitivity is peaked by physically sliding the antenna coil G along the ferrite rod to find the sweet spot. 

4. Short Wave (SW): * Aligned at 6.1 MHz using coil adjustments and then checked at 17.9 MHz for peak reception using trimmer K. 

Special Tools

• Signal Injection Coil: To avoid loading the circuit and changing the impedance, the restorer 3D-printed a custom "radiating coil." This coil sits near the radio's internal ferrite antenna and wirelessly "broadcasts" the test signal from the generator into the radio. 

• Non-Conductive Tools: He emphasizes using plastic or insulated tools to adjust the cores, as metal screwdrivers will shift the tuning and can easily crack the fragile ferrite cores. 

The Result

The radio is now highly sensitive on all AM bands, with the dial pointer tracking accurately across the scale. The restorer hints that the next challenge will be "stretching" the FM band to reach modern stations. 

Video Link: How to extend tuning range with an FM RF alignment

In Part 13, the restoration focus shifts to the FM RF alignment for the Nordmende Reulette 59. The goal is twofold:achieving proper dial accuracy and, uniquely, "stretching" the radio’s range to receive modern stations above its original 100 MHz limit. 

The FM Front-End Box

FM alignment involves the shielded metal box containing the ECC85 tube. This box is sensitive to high-frequency interference and physical changes. 

• The Circuit: Like the AM section, it uses two tuned circuits: a front-end pre-selector (to filter incoming signals) and a local oscillator (to mix the signal to the 10.7 MHz IF). 

• Caution: The restorer warns against messing with adjustments not mentioned in the service manual, as this can destabilize the high-frequency circuit and make it non-functional. 

The "Stretch" Technique

Original 1950s European radios typically only tuned up to 100 MHz. To pick up a favorite station at 101.6 MHz, the restorer intentionally misaligns the dial to "squish" the frequency range. 

1. Bottom End: He sets his signal generator to 87.5 MHz and adjusts Point D (oscillator coil) until the signal peaks at the very bottom of the dial. 

2. Top End (The Stretch): He sets the generator to 102 MHz and adjusts Point C (trimmer capacitor) until the radio receives this signal while the pointer is at the 100 MHz mark. 

3. The Trade-off: While the radio can now receive higher frequencies, the markings on the dial glass no longer perfectly match the actual stations. 

Tools and Alternatives

• The ELV SUP3: Since standard signal generators often don't cover the full FM band or provide stereo/RDS signals, the restorer uses a specialized stereo FM signal generator. 

• No Signal Generator? You can perform a "real-world" alignment by using two known local stations—one near the bottom of the dial (e.g., 88 MHz) and one near the top (e.g., 98 or 100 MHz). Use these as reference points to adjust the coils and trimmers until reception is clear at both ends. 

The Result

By adjusting the oscillator and peaking the antenna circuit, the radio's capability is increased by roughly 20%, allowing it to pick up modern stations that were previously out of reach.