Allied Model 435 Receiver Restoration

Unit: AM/FM Stereo Receiver

Manufacturer: Allied

Model: 435

SN: QG 16205

Today I am featuring a vintage Allied Model 435 receiver that came in for restoration. The information available online about this model could be more extensive. I was only able to find basic information. Apparently, this receiver was introduced in 1973. Output power is only 7.5 W per channel into 8 ohms. The retail price in 1973 was $179.95 (Ref. Radio Shack, 50th Anniversary Electronics Catalog 1973, page 97).

Note. The scanning quality of the instruction manual available online for this model is very poor. I have tried to identify each electronic component as accurately as possible, but some errors may still exist.

Power Supply Board (W16-030)

The power supply board has 3 aluminum electrolytic capacitors: C1, C2, and C3. All of them were replaced with low-impedance Nichicon UPW caps.

The original e-caps were tested with an Atlas ESR70 capacitance meter; the results are below. Almost all electrolytic capacitors on all boards deviated by more than 20% from the nominal capacitance.

Test results on original capacitors removed from the power supply board:

C1: rated capacitance – 100uF, measured – 123uF, ESR – 0.48Ω, deviation: +23%

C2: rated capacitance – 10uF, measured – 16uF, ESR – 5.8Ω, deviation: +60%

C3: rated capacitance – 100uF, measured – 124uF, ESR – 0.59Ω, deviation: +24%

I also replaced both NPN transistors on this board to improve the reliability of the power supply. Below is a list of original and replacement transistors that I have used.

Q1: NPN, 2SC968 (original), replaced with a new Fairchild KSC2383YBU

Q2: NPN, 2SC971 (original), replaced with a new Fairchild KSC2690AYSTU

Power supply board - before and after

Audio Unit (W15-043)

The audio unit has 21 aluminum electrolytic capacitors (C301, C302, C307, C308, C311, C312, C313, C314, C315, C316, C317, C318, C327, C328, C331, C332, C341, C342, C345, C346, C347) and two bi-polar e-caps (C329, C330).

All ordinary aluminum e-caps installed in the signal path, except for C313 and C314, were replaced with low-leakage Nichicon UKL capacitors to reduce the noise generated in the circuit. The original capacitors C313 and C314 were replaced with high-quality film polyester WIMA caps. Two original bi-polar capacitors were replaced with new bi-polar Nichicon UES caps. The remaining aluminum e-caps were replaced with low-impedance Nichicon UPW caps.

Test results on original capacitors removed from the audio unit:

C301: rated capacitance – 3.3uF, measured – 4.2uF, ESR – 2.7Ω, deviation: +27%

C302: rated capacitance – 3.3uF, measured – 4.5uF, ESR – 3.2Ω, deviation: +36%

C307: rated capacitance – 10uF, measured – 15uF, ESR – 2.8Ω, deviation: +50%

C308: rated capacitance – 10uF, measured – 13uF, ESR – 2.6Ω, deviation: +30%

C311: rated capacitance – 220uF, measured – 329uF, ESR – 0.24Ω, deviation: +50%

C312: rated capacitance – 220uF, measured – 286uF, ESR – 0.26Ω, deviation: +30%

C313: rated capacitance – 1uF, measured – 1.8uF, ESR – 3.1Ω, deviation: +80%

C314: rated capacitance – 1uF, measured – 1.6uF, ESR – 2.7Ω, deviation: +60%

C315: rated capacitance – 3.3uF, measured – 3.9uF, ESR – 2.8Ω, deviation: +18%

C316: rated capacitance – 3.3uF, measured – 4.5uF, ESR – 3.4Ω, deviation: +36%

C317: rated capacitance – 47uF, measured – 64uF, ESR – 1.22Ω, deviation: +36%

C318: rated capacitance – 47uF, measured – 66uF, ESR – 1.16Ω, deviation: +40%

C327: rated capacitance – 3.3uF, measured – 4.6uF, ESR – 3.2Ω, deviation: +39%

C328: rated capacitance – 3.3uF, measured – 4.3uF, ESR – 3.5Ω, deviation: +30%

C329: rated capacitance – 33uF, measured – 34uF, ESR – 1.02Ω, deviation: +3%

C330: rated capacitance – 33uF, measured – 33uF, ESR – 0.91Ω, deviation: 0%

C331: rated capacitance – 47uF, measured – 61uF, ESR – 0.66Ω, deviation: +30%

C332: rated capacitance – 47uF, measured – 69uF, ESR – 0.59Ω, deviation: +47%

C341: rated capacitance – 47uF, measured – 64uF, ESR – 1.14Ω, deviation: +36%

C342: rated capacitance – 47uF, measured – 60uF, ESR – 1.59Ω, deviation: +28%

C345: rated capacitance – 47uF, measured – 64uF, ESR – 1.24Ω, deviation: +36%

C346: rated capacitance – 47uF, measured – 61uF, ESR – 1.25Ω, deviation: +30%

C347: rated capacitance – 220uF, measured – 324uF, ESR – 0.32Ω, deviation: +47%

This board has two 2SC871 transistors installed in positions Q301/Q302 and six 2SC870 transistors installed in positions Q303 through Q308. Both are on my list of transistors prone to failure. I replaced them with a modern low-noise Fairchild KSC1845. Watch pinout when replacing transistors. The original 2SC870/2SC871 transistor is BCE, and the new one (KSC1845) is ECB.

Audio unit - before and after

Tuner Unit (W35-036)

The tuner board has 11 aluminum electrolytic capacitors: C35, C41, C62, C66, C72, C73, C78, C79, C82, C88, and C89. 

All original e-caps with a nominal capacitance of 1uF or less were replaced with film polyester WIMA caps. The remaining aluminum e-caps were replaced with low-impedance Nichicon UPW caps.

Test results on original capacitors removed from the tuner unit:

C35: rated capacitance – 0.47uF, measured – 0.58uF, ESR – N/A, deviation: +23%

C41: rated capacitance – 4.7uF, measured – 7.1uF, ESR – 2.1Ω, deviation: +51%

C62: rated capacitance – 4.7uF, measured – 7.2uF, ESR – 2.4Ω, deviation: +53%

C66: rated capacitance – 1uF, measured – 1.5uF, ESR – 2.7Ω, deviation: +50%

C72: rated capacitance – 0.47uF, measured – 0.82uF, ESR – N/A, deviation: +75%

C73: rated capacitance – 100uF, measured – 145uF, ESR – 0.52Ω, deviation: +45%

C78: rated capacitance – 100uF, measured – 152uF, ESR – 0.41Ω, deviation: +52%

C79: rated capacitance – 33uF, measured – 56uF, ESR – 0.49Ω, deviation: +70%

C82: rated capacitance – 0.47uF, measured – 0.88uF, ESR – N/A, deviation: +87%

C88: rated capacitance – 0.47uF, measured – 0.81uF, ESR – N/A, deviation: +72%

C89: rated capacitance – 0.47uF, measured – 0.83uF, ESR – N/A, deviation: +77%

This board also has 5 prone-to-failure transistors (2SC711 and 2SC710) installed in positions Q8 through Q12. I replaced them with a low-noise Fairchild KSC1845 transistor. Watch pinout when replacing transistors. The original 2SC710/2SC711 transistor is BCE, and the new one (KSC1845) is ECB.

Tuner unit - before and after

Main Filter and Two Coupling Capacitors

The original filter capacitor C3 was replaced with a new Nichicon LKG capacitor. The new capacitor is slightly larger in diameter compared to the original (25 mm versus 22 mm). To compensate for this difference, I installed a new Kemet clamp.

The original axial coupling capacitors C9 and C10 installed in the output signal path were replaced with new Vishay axial e-caps (138 AML series).

Test results on the original filter and coupling capacitors:

C3: rated capacitance – 1000uF, measured – 1520uF, ESR – 0.27Ω, deviation: +52%

C9: rated capacitance – 1000uF, measured – 1484uF, ESR – 0.18Ω, deviation: +48%

C10: rated capacitance – 1000uF, measured – 1668uF, ESR – 0.24Ω, deviation: +67%

Original and new main filter capacitor

New axial coupling capacitors (sorry, I forgot to take a picture of the original coupling caps)

Dial, Dial Pointer, Meter, and Stereo Indicator Lamps

Replacing the dial lamps on this receiver is a simple task. Just remove the front panel and pull out the lamps from their sockets. I replaced the old incandescent bulbs with warm white LED lamps to maintain the original look and decrease heat.

Dial lamps - before and after

Replacing the dial pointer lamp in almost any vintage receiver is the most tedious job. This is very delicate work and there is always a chance of breaking the tiny and fragile pointer. So, pay extra attention while replacing this lamp. The original dial pointer lamp burned out in this unit and I replaced it with a new 4.7mm incandescent lamp.

Dial pointer lamp - before and after

The rubber socket for the stereo indicator lamp is still in great shape and I replaced the old bulb with a new 4.7mm incandescent lamp.

Stereo indicator lamp - before and after

Output Power Test

The final output power test was performed at the end of my restoration. The receiver was loaded with a low inductance 8Ω/100W dummy resistor for each channel. The oscilloscope was connected across the speaker terminals and a sine-wave signal of 1kHz was applied to the AUX jacks. The output sine-wave signal was perfectly symmetrical on both channels with no clipping up to 7.25 VRMS (left channel) and 7.35 VRMS (right channel). It corresponds to the output power of 6.6W on the left channel and 6.8W on the right channel.

Output power test

As usual, all the knobs and the front panel were gently cleaned in warm water with dish soap. All controls have been cleaned with DeoxIT 5% contact cleaner and lubricated with DeoxIT FaderLube 5% spray.

The final result can be seen in the photos below. This receiver sounds very good! Please watch a short demo video at the end of this post. Thank you for reading.

Allied Model 435 - after restoration

Demo video after repair & restoration

McIntosh MA 6100 Stereo Integrated Amplifier Restoration

Unit: Stereo Integrated Amplifier

Manufacturer: McIntosh

Model: MA 6100

SN: AE8043

Today I'm showing a magnificent McIntosh MA 6100 integrated amplifier that came in for restoration.

The MA 6100 is a solid-state, direct-coupled amplifier that was manufactured from 1972 to 1979. It produces 70 watts per channel into 8 ohms with no more than 0.2% total harmonic distortion. The damping factor at 8 ohms is 50. The retail price in 1975 was $699.00. An interesting review of this model was published in Modern Recording, Vol. 1 No. 3, page 50, 1976.

Left and Right Channel PreAmp Board (044-512)

Each preamp board has one ROE electrolytic capacitor (C107/C108) and 3 ordinary aluminum electrolytic capacitors: C105/C106, C113/C114, C123/C124. 

The original ROE e-caps (EK Series with Bakelite Case and encapsulant) were replaced with modern low-leakage Nichicon UKL caps. The remaining aluminum e-caps were replaced with low-impedance Nichicon UPW caps.

All original e-caps were tested with an Atlas ESR70 capacitance meter; the results are below.

Please note that the 4 original capacitors installed on these two boards drifted from the nominal capacitance by more than 40%. The measured capacitance of original ROE e-caps C107 and C108 is almost double their rated capacitance!

Test results on original capacitors removed from the left and right channel PreAmp boards:

C105: rated capacitance – 10uF, measured – 11uF, ESR – 1.93Ω, deviation: +10%

C106: rated capacitance – 10uF, measured – 11uF, ESR – 2.11Ω, deviation: +10%

C107: rated capacitance – 10uF, measured – 18uF, ESR – 0.75Ω, deviation: +80%

C108: rated capacitance – 10uF, measured – 20uF, ESR – 0.98Ω, deviation: +100%

C113: rated capacitance – 100uF, measured – 119uF, ESR – 0.44Ω, deviation: +19%

C114: rated capacitance – 100uF, measured – 146uF, ESR – 1.31Ω, deviation: +46%

C123: rated capacitance – 100uF, measured – 108uF, ESR – 0.42Ω, deviation: +8%

C124: rated capacitance – 100uF, measured – 141uF, ESR – 0.63Ω, deviation: +41%

Two original carbon resistors with 5% tolerance (R115, R116) were replaced with 1% tolerance KOA Speer metal film resistors. The other two carbon resistors with 5% tolerance (R117, R118) were replaced with 1% tolerance Yageo metal film resistors.

I also decided to unsolder and test each pair of original BC109C transistors installed in the differential amplifier (Q107/Q109 and Q108/Q110) to assess their matching. Each pair of transistors is supposed to be precisely matched to work properly in the circuit. Below are the testing results for the original BC109C transistors from each channel.

Test results on original BC109C transistors

Q107 (left channel): hfe - 545, Vbe - 0.737V

Q109 (left channel): hfe - 476, Vbe - 0.754V

Q108 (right channel): hfe - 549, Vbe - 0.765V

Q110 (right channel): hfe - 548, Vbe - 0.762V

The mismatch between the two transistors in the left channel is approximately 14%. This level of mismatch is quite high and can result in a high DC offset. In contrast, in the right channel, the mismatch between the two transistors is almost 0%.

I decided to replace all the OEM transistors with the new Central Semiconductor BC109C to ensure the differential amplifier circuit was working properly. Before installation, each pair of BC109C transistors was meticulously matched for current gain and base-emitter voltage.

Test results on new closely matched BC109C transistors

Q107 (left channel): hfe - 619, Vbe - 0.767V

Q109 (left channel): hfe - 618, Vbe - 0.769V

Q108 (right channel): hfe - 617, Vbe - 0.768V

Q110 (right channel): hfe - 618, Vbe - 0.769V

The original BC109C transistors installed in positions Q111 and Q112 were also replaced with new Central Semiconductor BC109C transistors.

Left channel PreAmp board - before and after

Right channel PreAmp board - before and after

Left and Right Channel Power Output Boards (044-585)

Each power output board has one solid tantalum capacitor (C427/C428) installed in the input signal path, one axial filtering e-cap (C401/C402), one ROE bi-polar e-cap (C419/C420) installed in the crowbar circuit, and one radial aluminum electrolytic capacitor (C403/C404).

The original tantalum capacitors were replaced with high-quality film polyester WIMA caps. The original axial capacitors were replaced with new axial Vishay  caps. The original bi-polar ROE e-caps (EKU Series with Bakelite Case and encapsulant) were replaced with new bi-polar Nichicon UES caps. The remaining aluminum e-caps were replaced with low-impedance Nichicon UPW caps.

Test results on original capacitors removed from the left and right channel power output boards:

C401: rated capacitance – 150uF, measured – 161uF, ESR – 0.38Ω, deviation: +7%

C402: rated capacitance – 150uF, measured – 152uF, ESR – 0.26Ω, deviation: +1%

C403: rated capacitance – 100uF, measured – 123uF, ESR – 0.68Ω, deviation: +23%

C404: rated capacitance – 100uF, measured – 122uF, ESR – 1.43Ω, deviation: +22%

C419: rated capacitance – 10uF, measured – 12uF, ESR – 0.66Ω, deviation: +20%

C420: rated capacitance – 10uF, measured – 13uF, ESR – 0.68Ω, deviation: +30%

C427: rated capacitance – 1.5uF, measured – 1.6uF, ESR – 9.2Ω, deviation: +7%

C428: rated capacitance – 1.5uF, measured – 1.7uF, ESR – 8.8Ω, deviation: +13%

All original carbon resistors with 5% tolerance (R405, R406, R411, R412, R421, R422, R423, R424) were replaced with 1% tolerance KOA Speer metal film resistors.

Left channel power output board - before and after

Right channel power output board - before and after

Reg & Phase Inverter Board (044-419)

This board has one radial aluminum electrolytic capacitor C302, and 2 axial e-caps (C303, C307).

This board was previously serviced and a low-quality Jamicon e-cap was installed in position C302. The service manual calls for this position a solid tantalum capacitor. I replaced it with a modern low-leakage Nichicon UKL cap. The original axial capacitors were with new axial Vishay caps.

Test results on original capacitors removed from the reg & phase inverter board:

C302: rated capacitance – 10uF, measured – 11uF, ESR – 1.04Ω, deviation: +10%

C303: rated capacitance – 33uF, measured – 41uF, ESR – 0.32Ω, deviation: +24%

C307: rated capacitance – 100uF, measured – 132uF, ESR – 0.77Ω, deviation: +32%

Reg & phase inverter board - before and after

Power Supply Section (154-616)

The power supply section has one triple electrolytic capacitor C312 (sections A, B, and C), 2 main filter capacitors (C313, C314), and one axial e-cap C317.

The original triple e-cap C312 (sections B and C) and two main filter caps (C313, C314) were tested in-circuit with Atlas ESR70 capacitance meter. These capacitors are still within the factory capacitance tolerance and have very low ESR.

In-circuit test on triple e-cap C312 and two main filter capacitors C313 & C314

C312B: rated capacitance – 150uF, measured – 178uF, ESR – 0.81Ω, deviation: +19%

C312C: rated capacitance – 150uF, measured – 176uF, ESR – 0.64Ω, deviation: +17%

C313: rated capacitance – 9300uF, measured – 10360uF, ESR – 0.12Ω, deviation: +11%

C314: rated capacitance – 9300uF, measured – 10440uF, ESR – 0.11Ω, deviation: +12%

The original axial e-cap C317 was replaced with a new axial Vishay capacitor.

Test result on original capacitor removed from the power supply section:

C317: rated capacitance – 220uF, measured – 237uF, ESR – 0.16Ω, deviation: +8%

Axial electrolytic capacitor C317 - original and new

Panel Illumination and Switch Indicator Lamps

The MA 6100 has 4 panel illumination lamps (bayonet base, #1866) and 4 switch indicator lamps (bayonet base, #51). The panel lights are fairly easy to remove by simply pushing them in and twisting. However, the indicator lamps are deeply recessed and require some tools and effort to remove them.

I replaced all original incandescent lamps with warm white LED lamps except the far left and far right lamps. These two lamps were replaced with new incandescent lamps.

Note that the old foam strips around the push button switches have degraded and falling apart due to age. I replaced them with new foam strips to prevent light leaking through the display. 

Original incandescent lamps and crumbly foam strips around pushbutton switches

New warm white LED lamps and new foam strips around pushbutton switches

Output Power Test

The final output power test was performed at the end of my restoration. The amplifier was loaded with a low inductance 8Ω/100W dummy resistor for each channel. The oscilloscope was connected across the speaker terminals and a sine-wave signal of 1kHz was applied to the AUX jacks. The output sine-wave signal was perfectly symmetrical on both channels with no clipping up to 25.23 VRMS (left channel) and 25.34 VRMS (right channel). It corresponds to the output power of 79.6W on the left channel and 80.3W on the right channel.

Output power test

As usual, all the knobs were cleaned in warm water with dish soap. The front panel was carefully wiped with a piece of damp cloth. All controls have been cleaned with DeoxIT 5% contact cleaner and lubricated with DeoxIT FaderLube 5% spray.

The final result can be seen in the photos below. This unit looks and sounds amazing. Please watch a short demo video at the end of this post. Thank you for reading.

McIntosh MA 6100 - after restoration

Demo video after repair & restoration

Luxman L-80V Stereo Integrated Amplifier Restoration

Unit: Stereo Integrated Amplifier

Manufacturer: Luxman

Model: L-80V

SN: I6507821

Today I'm showing a gorgeous Luxman L-80V integrated amplifier that came in for restoration. This model was manufactured from 1978 to 1979. It produces 50 watts per channel into 8 ohms with no more than 0.05% total harmonic distortion. The damping factor at 8 ohms is 40. The list price in 1978 was $475.00 (Ref. Stereo Directory & Buying Guide, 1978, page 44).

Main Amplifier, Ripple Filter & Muting Protector Board (PB-891)

Main Amplifier Circuit

The main amplifier circuit has 2 solid tantalum capacitors (C101a, C101b) installed in the signal path and 12 aluminum electrolytic capacitors: C103a, C103b, C104a, C104b, C107a, C107b, C108a, C108b, C111a, C111b, C112, C114.

Both original solid tantalum capacitors were replaced with modern low-leakage Nichicon UKL caps. Two aluminum e-caps with a nominal capacitance of 1uF (C112 and C114) were replaced with high-quality film polyester WIMA caps. And the remaining e-caps were replaced with low-impedance Nichicon UPW/UPM capacitors.

The original e-caps were tested with an Atlas ESR70 capacitance meter; the results are below.

Test results on original capacitors removed from the main amplifier circuit:

C101a: rated capacitance – 10uF, measured – 12uF, ESR – 0.44Ω, deviation: +20%

C101b: rated capacitance – 10uF, measured – 12uF, ESR – 0.62Ω, deviation: +20%

C103a: rated capacitance – 100uF, measured – 121uF, ESR – 0.28Ω, deviation: +21%

C103b: rated capacitance – 100uF, measured – 139uF, ESR – 0.22Ω, deviation: +39%

C104a: rated capacitance – 100uF, measured – 128uF, ESR – 0.18Ω, deviation: +28%

C104b: rated capacitance – 100uF, measured – 125uF, ESR – 0.25Ω, deviation: +25%

C107a: rated capacitance – 33uF, measured – 41uF, ESR – 1.08Ω, deviation: +24%

C107b: rated capacitance – 33uF, measured – 39uF, ESR – 1.12Ω, deviation: +18%

C108a: rated capacitance – 100uF, measured – 127uF, ESR – 0.14Ω, deviation: +27%

C108b: rated capacitance – 100uF, measured – 124uF, ESR – 0.16Ω, deviation: +24%

C111a: rated capacitance – 470uF, measured – 680uF, ESR – 0.22Ω, deviation: +45%

C111b: rated capacitance – 470uF, measured – 594uF, ESR – 0.32Ω, deviation: +26%

C112: rated capacitance – 1uF, measured – 1.1uF, ESR – 2.2Ω, deviation: +10%

C114: rated capacitance – 1uF, measured – 1.0uF, ESR – 2.8Ω, deviation: 0%

Equalizer Amplifier Circuit

The equalizer amplifier has 2 solid tantalum capacitors (C201a, C202b) installed in the input signal path and 2 low-leakage e-caps (C202a, C202b). 

The original solid tantalum and low-leakage e-caps were replaced with modern low-leakage Nichicon UKL caps.

Test results on original capacitors removed from the equalizer amplifier circuit:

C201a: rated capacitance – 2.2uF, measured – 2.4uF, ESR – 1.02Ω, deviation: +9%

C201b: rated capacitance – 2.2uF, measured – 2.4uF, ESR – 0.88Ω, deviation: +9%

C202a: rated capacitance – 22uF, measured – 23uF, ESR – 0.42Ω, deviation: +5%

C202b: rated capacitance – 22uF, measured – 22uF, ESR – 0.40Ω, deviation: 0%

Protection Circuit

The protection circuit has 4 aluminum electrolytic capacitors: C601, C602, C603, and C604. All of them were replaced with low-impedance Nichicon UPW/UPM capacitors.

Test results on original capacitors removed from the protection circuit:

C601: rated capacitance – 22uF, measured – 27uF, ESR – 0.62Ω, deviation: +23%

C602: rated capacitance – 220uF, measured – 223uF, ESR – 0.28Ω, deviation: +1%

C603: rated capacitance – 220uF, measured – 278uF, ESR – 0.18Ω, deviation: +26%

C604: rated capacitance – 220uF, measured – 293uF, ESR – 0.24Ω, deviation: +33%

Ripple Filter Circuit

The ripple filter circuit has 8 aluminum electrolytic capacitors: C705, C706, C709, C710, C711, C713, and C714. All of them were replaced with low-impedance Nichicon UPW/UPM capacitors.

Test results on original capacitors removed from the ripple filter circuit:

C705: rated capacitance – 220uF, measured – 215uF, ESR – 0.24Ω, deviation: -2%

C706: rated capacitance – 220uF, measured – 230uF, ESR – 0.26Ω, deviation: +5%

C709: rated capacitance – 100uF, measured – 100uF, ESR – 0.44Ω, deviation: 0%

C710: rated capacitance – 100uF, measured – 97uF, ESR – 0.34Ω, deviation: -3%

C711: rated capacitance – 100uF, measured – 98uF, ESR – 0.41Ω, deviation: -2%

C712: rated capacitance – 47uF, measured – 58uF, ESR – 0.37Ω, deviation: +23%

C713: rated capacitance – 100uF, measured – 98uF, ESR – 0.31Ω, deviation: -2%

C714: rated capacitance – 100uF, measured – 102uF, ESR – 0.34Ω, deviation: +2%

The original speaker protection relay in this amplifier was previously replaced with a new Omron MY2-02-DC24 relay. It is still in great shape and I retained it.

The original trimming resistors were replaced with new Bourns potentiometers.

Main amplifier, ripple filter & muting protector board - before and after

Filter & Boost Amplifier Board (PB-892)

The filter & boost amplifier board has 4 solid tantalum capacitors (C301a, C301b, C308a, C308b) installed in the signal path, and 7 aluminum electrolytic capacitors (C302a, C302b, C304a, C304b, C305, C306a, C306b).

The original solid tantalum capacitors were replaced with modern low-leakage Nichicon UKL caps. The remaining aluminum e-caps were replaced with low-impedance Nichicon UPW capacitors.

Test results on original capacitors removed from the filter & boost amplifier board:

C301a: rated capacitance – 4.7uF, measured – 4.9uF, ESR – 0.46Ω, deviation: +4%

C301b: rated capacitance – 4.7uF, measured – 4.9uF, ESR – 0.86Ω, deviation: +4%

C302a: rated capacitance – 33uF, measured – 38uF, ESR – 1.04Ω, deviation: +15%

C302b: rated capacitance – 33uF, measured – 39uF, ESR – 1.11Ω, deviation: +18%

C304a: rated capacitance – 47uF, measured – 59uF, ESR – 0.98Ω, deviation: +26%

C304b: rated capacitance – 47uF, measured – 59uF, ESR – 0.92Ω, deviation: +26%

C305: rated capacitance – 100uF, measured – 91uF, ESR – 0.28Ω, deviation: -9%

C306a: rated capacitance – 100uF, measured – 136uF, ESR – 0.94Ω, deviation: +36%

C306b: rated capacitance – 100uF, measured – 138uF, ESR – 0.62Ω, deviation: +38%

C308a: rated capacitance – 2.2uF, measured – 2.2uF, ESR – 0.82Ω, deviation: 0%

C308b: rated capacitance – 2.2uF, measured – 2.2uF, ESR – 0.52Ω, deviation: 0%

Filter & boost amplifier board - before and after

Tone Control Amplifier Board (PB-893)

The tone control amplifier board has 4 solid tantalum capacitors (C405a, C405b, C409a, C409b) installed in the signal path, and 3 aluminum electrolytic capacitors (C406a, C406b, C408).

The original solid tantalum capacitors were replaced with modern low-leakage Nichicon UKL caps. The remaining aluminum e-caps were replaced with low-impedance Nichicon UPW capacitors.

Test results on original capacitors removed from the tone control amplifier board:

C405a: rated capacitance – 4.7uF, measured – 4.9uF, ESR – 0.58Ω, deviation: +4%

C405b: rated capacitance – 4.7uF, measured – 4.9uF, ESR – 0.55Ω, deviation: +4%

C406a: rated capacitance – 100uF, measured – 112uF, ESR – 0.48Ω, deviation: +12%

C406b: rated capacitance – 100uF, measured – 115uF, ESR – 0.59Ω, deviation: +15%

C408: rated capacitance – 100uF, measured – 99uF, ESR – 0.28Ω, deviation: -1%

C409a: rated capacitance – 2.2uF, measured – 2.2uF, ESR – 0.66Ω, deviation: 0%

C409b: rated capacitance – 2.2uF, measured – 2.1uF, ESR – 0.82Ω, deviation: -5%

Tone control amplifier board - before and after

DC offset and Bias Adjustments

Be aware, that the service manual has an error for DC offset and bias adjustments. The correct procedure is described below.

The DC offset on the left and right channels is measured across the speaker terminals (make sure the speaker button is pressed). The DC offset should be adjusted as close to zero volts as possible with the trimming resistor VR101 on each channel.

The Bias is measured across two emitter resistors R123 and R124 on each channel. So, the voltmeter should be connected between terminal P103 (+) and terminal P104 (-). The Bias should be adjusted to ~23mV on each channel with the trimming resistor VR102.

DC offset on the left and right channels after restoration

Bias on the left and right channels after restoration

Output Power Test

The final output power test was performed at the end of my restoration. The amplifier was loaded with a low inductance 8Ω/100W dummy resistor for each channel. The oscilloscope was connected across the speaker terminals and a sine-wave signal of 1kHz was applied to the AUX jacks. The output sine-wave signal was perfectly symmetrical on both channels with no clipping up to 20.34 VRMS (left channel) and 20.55 VRMS (right channel). It corresponds to the output power of 51.7W on the left channel and 52.8W on the right channel.

Output power test

As usual, all the knobs and the front panel were gently cleaned in warm water with dish soap. All controls have been cleaned with DeoxIT 5% contact cleaner and lubricated with DeoxIT FaderLube 5% spray.

The final result can be seen in the photos below. This integrated amplifier looks and sounds truly amazing. Please watch a short demo video at the end of this post. Thank you for reading.

Luxman L-80V - after restoration

Demo video after repair & restoration