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Saturday, May 18, 2024

Marantz 2265B Receiver Restoration

Unit: AM/FM Stereo Receiver
Manufacturer: Marantz
Model: 2265B
SN: U130304

Today I'm showcasing a Marantz 2265B vintage receiver that came in for restoration. Marantz 2265B was manufactured from 1977 to 1979. It produces 65 watts per channel into 8 ohms with no more than 0.05% total harmonic distortion. The damping factor at 8 ohms is 55. The optional walnut veneer cabinet for this model is WC-122.

Marantz 2265B_after restoration

According to the factory stamp on the chassis, this receiver was manufactured in June 1978.

Power Supply Board (P800)

The power supply board has 14 aluminum electrolytic capacitors: C801, C802, C803, C804, C806, C809, C810, C812, C813, C815, C817, C818, C819, and C820.

I replaced all capacitors on this board with low-impedance Nichicon UPW/UPM caps.

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

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

C801: rated capacitance – 470uF, measured – 447uF, ESR – 0.32Ω, deviation: -5%
C802: rated capacitance – 330uF, measured – 271uF, ESR – 0.75Ω, deviation: -18%
C803: rated capacitance – 100uF, measured – 115uF, ESR – 0.56Ω, deviation: +15%
C804: rated capacitance – 47uF, measured – 52uF, ESR – 0.73Ω, deviation: +11%
C806: rated capacitance – 10uF, measured – 12uF, ESR – 0.77Ω, deviation: +20%
C809: rated capacitance – 330uF, measured – 372uF, ESR – 0.31Ω, deviation: +13%
C810: rated capacitance – 470uF, measured – 466uF, ESR – 0.38Ω, deviation: -1%
C812: rated capacitance – 10uF, measured – 9uF, ESR – 0.95Ω, deviation: -10%
C813: rated capacitance – 100uF, measured – 111uF, ESR – 0.69Ω, deviation: +11%
C815: rated capacitance – 100uF, measured – 78uF, ESR – 0.56Ω, deviation: -22%
C817: rated capacitance – 4.7uF, measured – 4.5uF, ESR – 3.6Ω, deviation: -4%
C818: rated capacitance – 47uF, measured – 49uF, ESR – 0.88Ω, deviation: +4%
C819: rated capacitance – 220uF, measured – 211uF, ESR – 0.67Ω, deviation: -4%
C820: rated capacitance – 470uF, measured – 492uF, ESR – 0.34Ω, deviation: +5%

All transistors and two Zener diodes on this board were also replaced to improve the reliability of the power supply. Below is a list of original and replacement parts that I have used.

Q801: NPN, 2SC1567 (original), replaced with a new Fairchild KSC2690AYSTU
Q802: NPN, 2SC1318 (original), replaced with a new Fairchild KSC2690AYSTU
Q803: PNP, 2SA794 (original), replaced with a new Fairchild KSA1220AYS
Q804: PNP, 2SA684 (original), replaced with a new Fairchild KSA1220AYS
Q805: Zener, 19.2V/0.5W, WZ-192 (original), replaced with a new Fairchild 1N5249BTR
Q806: NPN, 2SC1384 (original), replaced with a new Fairchild KSC2690AYSTU
Q807: PNP, 2SA684 (original), replaced with a new Fairchild KSA1220AYS
Q808: NPN, 2SD313 (original), replaced with a new Fairchild MJE15030G
Q809: Zener, 14V/0.5W, WZ-140 (original), replaced with a new Fairchild 1N5244B
Q810: NPN, 2SC945 (original), replaced with a new Fairchild KSC945CYTA
Q811: NPN, 2SC1318 (original), replaced with a new Fairchild KSC2383YTA
Q812: NPN, 2SC1318 (original), replaced with a new Fairchild KSC2383YTA

The original protection relay in this unit was already replaced with a new Omron relay.

Power supply board - before servicing

Marantz 2265B_Power Supply Board (P800)_before servicing_01

Marantz 2265B_Power Supply Board (P800)_before servicing_02

Power supply board - after servicing

Marantz 2265B_Power Supply Board (P800)_after servicing_01

Marantz 2265B_Power Supply Board (P800)_after servicing_02

Main Amplifier Board (P700)

The main amplifier board has 8 low-leakage e-caps (C701, C706, C716, C717, C751, C756, C766, C767) and 6 ordinary aluminum electrolytic capacitors (C710, C722, C723, C760, C772, C773).

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

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

C701: rated capacitance – 4.7uF, measured – 4.7uF, ESR – 5.7Ω, deviation: 0%
C706: rated capacitance – 47uF, measured – 46uF, ESR – 1.04Ω, deviation: -2%
C710: rated capacitance – 47uF, measured – 48uF, ESR – 0.56Ω, deviation: +2%
C716: rated capacitance – 10uF, measured – 11uF, ESR – 1.87Ω, deviation: +10%
C717: rated capacitance – 10uF, measured – 11uF, ESR – 1.76Ω, deviation: +10%
C722: rated capacitance – 220uF, measured – 225uF, ESR – 0.34Ω, deviation: +2%
C723: rated capacitance – 220uF, measured – 222uF, ESR – 2.1Ω, deviation: +1%
C751: rated capacitance – 4.7uF, measured – 5.2uF, ESR – 5.1Ω, deviation: +11%
C756: rated capacitance – 47uF, measured – 44uF, ESR – 0.94Ω, deviation: -6%
C760: rated capacitance – 47uF, measured – 49uF, ESR – 0.76Ω, deviation: +4%
C766: rated capacitance – 10uF, measured – 11uF, ESR – 1.63Ω, deviation: +10%
C767: rated capacitance – 10uF, measured – 11uF, ESR – 1.95Ω, deviation: +10%
C772: rated capacitance – 220uF, measured – 239uF, ESR – 0.35Ω, deviation: +9%
C773: rated capacitance – 220uF, measured – 219uF, ESR – 0.47Ω, deviation: -1%

The four original capacitors installed on this board were secured at the factory with glue. Before installing the new capacitors, I removed the old glue but noticed that two resistors (R709 and R759) located next to capacitors C723 and C753 were also covered in old glue. I decided to replace them with new KOA Speer metal film resistors to prevent possible degradation in the future.

The first stage of the main amplifier circuit is a differential amplifier consisting of two amplifying transistors with a common emitter: Q701/Q702 and Q751/Q752. The original PNP transistor installed in these positions is 2SA722. This transistor is not on my list of infamous transistors that are prone to failure. However, testing each pair of transistors installed in the differential amplifier always makes sense to ensure they are still well-matched. 

As can be seen from the test below, the mismatch of each pair of original transistors in the left and right channels is ~14% and ~16%, respectively. I prefer to keep the mismatch between the two transistors in a differential amplifier as small as possible since it is critical to the correct operation of this circuit. So I replaced each pair of the original 2SA722s with a closely matched pair (within 1%) of modern Fairchild KSA992 low-noise transistors. I put a slight smear of new thermal paste on one face of KSA992 and pressed both transistors together. Heat shrink tubing was used to hold them together mechanically.

Test results on original 2SA722 transistors

Q701 (left channel): hfe - 373, Vbe - 0.786V 
Q702 (left channel): hfe - 426, Vbe - 0.787V

Q751 (right channel): hfe - 397, Vbe - 0.786V 
Q752 (right channel): hfe - 342, Vbe - 0.787V

Test results on new KSA992FBU transistors

Q701 (left channel): hfe - 407, Vbe - 0.761V
Q702 (left channel): hfe - 407, Vbe - 0.763V

Q751 (right channel): hfe - 404, Vbe - 0.762V
Q752 (right channel): hfe - 405, Vbe - 0.761V

Each original MV-13 diode installed in positions Q703, Q704, Q753, and Q754 was replaced with two 1N4148 diodes connected in series.

All original trimming resistors were replaced with new Bourns potentiometers.

Main amplifier board - before and after

Marantz 2265B_Main Amplifier Board (P700)_before servicing

Marantz 2265B_Main Amplifier Board (P700)_after servicing

Pre and Tone Amplifier Board (PE01)

The pre and tone amplifier board has 14 low-leakage capacitors (CE01, CE02, CE03, CE04, CE09, CE10, CE31, CE32, CE39, CE40, CH11, CH12, CH15, CH16) installed in the signal path, and 4 aluminum electrolytic capacitors (CE35, CE36, CE43, CE44).

Four original low-leakage capacitors (CE01, CE02, CE31, CE32) installed in the input signal path were replaced with high-quality film polyester WIMA caps. Other original low-leakage e-caps were replaced with modern low-leakage Nichicon UKL caps. The remaining aluminum e-caps were replaced with low-impedance Nichicon UPW caps.

Pay attention to capacitor CE40. The polarity of CE40 is shown backward on the circuit board silkscreen. The negative lead of CE10 must be connected to pin JE10.

Tip: Disconnecting the solid white/black wire from the pre and tone amplifier board will give you more room to work with. Just remember to solder it back when you're done with this board.

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

CE01: rated capacitance – 1uF, measured – 0.9uF, ESR – 4.1Ω, deviation: -10%
CE02: rated capacitance – 1uF, measured – 1.0uF, ESR – 4.2Ω, deviation: 0%
CE03: rated capacitance – 33uF, measured – 38uF, ESR – 1.41Ω, deviation: +15%
CE04: rated capacitance – 33uF, measured – 41uF, ESR – 1.34Ω, deviation: +24%
CE09: rated capacitance – 4.7uF, measured – 5.3uF, ESR – 3.4Ω, deviation: +13%
CE10: rated capacitance – 4.7uF, measured – 4.8uF, ESR – 4.3Ω, deviation: +2%
CE31: rated capacitance – 1uF, measured – 1.0uF, ESR – 4.0Ω, deviation: 0%
CE32: rated capacitance – 1uF, measured – 1.0uF, ESR – 3.6Ω, deviation: 0%
CE35: rated capacitance – 3.3uF, measured – 3.6uF, ESR – 2.1Ω, deviation: +9%
CE36: rated capacitance – 3.3uF, measured – 3.8uF, ESR – 1.6Ω, deviation: +15%
CE39: rated capacitance – 4.7uF, measured – 5.3uF, ESR – 3.4Ω, deviation: +13%
CE40: rated capacitance – 4.7uF, measured – 5.6uF, ESR – 4.8Ω, deviation: +19%
CE43: rated capacitance – 100uF, measured – 121uF, ESR – 2.4Ω, deviation: +21%
CE44: rated capacitance – 100uF, measured – 118uF, ESR – 1.4Ω, deviation: +18%
CH11: rated capacitance – 2.2uF, measured – 2.0uF, ESR – 5.1Ω, deviation: -9%
CH12: rated capacitance – 2.2uF, measured – 2.0uF, ESR – 5.3Ω, deviation: -9%
CH15: rated capacitance – 10uF, measured – 9uF, ESR – 1.24Ω, deviation: -10%
CH16: rated capacitance – 10uF, measured – 9uF, ESR – 1.51Ω, deviation: -10%

Six NPN transistors (QE05, QE06, QE07, QE08, QH03, QH04) installed on this board are Hitachi 2SC1345. This transistor is on my list of transistors that are prone to failure. I replaced all original 2SC1345s with new Fairchild KSC1845 transistors. Watch the pinout on replacement transistors. The original transistor is BCE and the new one is ECB.

Pre and tone amplifier board - before and after

Marantz 2265B_Pre and Tone Amplifier Board (PE01)_before servicing

Marantz 2265B_Pre and Tone Amplifier Board (PE01)_after servicing

Monitor & Filter Switches Circuit Board (PS01)

The monitor & filter switches circuit board does not have electrolytic capacitors but contains three prone-to-failure transistors: 2SA720 (QS01), 2SC1345 (QH01 and QH02).

The original Panasonic 2SA720 was replaced with a new Fairchild KSA1013YBU transistor. The replacement transistor has the same pinout as the original one.

Both original Hitachi 2SC1345s were replaced with new Fairchild KSC1845 transistors. Watch the pinout on replacement transistors. The original transistor is BCE and the new one is ECB.

Monitor & filter switches board - before and after

Marantz 2265B_Monitor & Filter Switches Circuit Board (PS01)_before servicing

Marantz 2265B_Monitor & Filter Switches Circuit Board (PS01)_after servicing

All switches on this board can be easily cleaned and lubricated during the servicing. However, the "Tape Copy" and "Tape Monitor" switches are located between this and another small board, as seen in the photo below. The small top PCB must be removed to access all hidden switches for cleaning. This can be a challenging task for those who don't have the right tools. For this purpose, I used my Hakko FR301 desoldering tool, which greatly helped.

"Tape Copy" and "Tape Monitor" switches are sandwiched between two PCBs

Marantz 2265B_Tape Copy, Tape Monitor Switches_sandwiched between two PCBs

The small top PCB and extension shaft are removed - now it is easy to clean and lubricate

Marantz 2265B_Tape Copy, Tape Monitor Switches_top PCB and extension shaft removed

Phono Amplifier Board (P400)

The phono amplifier board has 6 low-leakage e-caps installed in the signal path (C401, C402, C409, C410, C417, C418) and two aluminum electrolytic capacitors (C423, C424).

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

Test results on original capacitors removed from the phono amplifier board:

C401: rated capacitance – 4.7uF, measured – 4.8uF, ESR – 2.4Ω, deviation: +2%
C402: rated capacitance – 4.7uF, measured – 5.0uF, ESR – 2.1Ω, deviation: +6%
C409: rated capacitance – 33uF, measured – 38uF, ESR – 2.2Ω, deviation: +15%
C410: rated capacitance – 33uF, measured – 37uF, ESR – 1.41Ω, deviation: +12%
C417: rated capacitance – 4.7uF, measured – 4.2uF, ESR – 2.8Ω, deviation: -11%
C418: rated capacitance – 4.7uF, measured – 4.2uF, ESR – 2.6Ω, deviation: -11%
C423: rated capacitance – 47uF, measured – 46uF, ESR – 0.44Ω, deviation: -2%
C424: rated capacitance – 47uF, measured – 48uF, ESR – 0.52Ω, deviation: +2%

I also replaced the original Hitachi 2SA872 transistors installed in the differential amplifier circuit with modern Fairchild KSA992 low-noise transistors. Each pair of new transistors is closed-matched within 1%. The replacement transistor has the same pinout as the original one.

Test results on original 2SA872 transistors

Q401 (left channel): hfe - 354, Vbe - 0.776V 
Q403 (left channel): hfe - 318, Vbe - 0.776V

Q402 (right channel): hfe - 355, Vbe - 0.779V 
Q404 (right channel): hfe - 316, Vbe - 0.781V

Test results on new KSA992FBU transistors

Q401 (left channel): hfe - 409, Vbe - 0.760V
Q403 (left channel): hfe - 410, Vbe - 0.761V

Q402 (right channel): hfe - 412, Vbe - 0.761V
Q404 (right channel): hfe - 414, Vbe - 0.763V

Phono amplifier board - before and after

Marantz 2265B_Phono Amplifier Board (P400)_before servicing

Marantz 2265B_Phono Amplifier Board (P400)_after servicing

Power Transistors

All power transistors were removed, degreased, and tested with an Atlas DCA55 semiconductor analyzer. According to the datasheet, the measured current gain on all transistors was in spec. 

However, it should be noted that the Atlas DCA55 Semiconductor Analyzer provides accurate DC gain readings only on low-power transistors. A high-power transistor requires a much higher collector current and collector-emitter voltage to accurately measure its current gain. However, it is still a handy device for comparing transistors of a similar type for gain matching or fault-finding.

I applied a fresh thermal compound and replaced the old thermal pads with new Mica ones which is always a good idea when working on any vintage receiver. The old grease can frequently dry, causing the transistors to suffer from poor heat dissipation. This can result in overheating and the destruction of the device.

Original power transistors

Marantz 2265B_Heat Sink and Power Transistors_before servicing

With new Mica pads

Marantz 2265B_Heat Sink and Power Transistors_after servicing

Main Filter Capacitors

Two main filter capacitors were tested with an Atlas ESR70 capacitance meter.  Both caps are still within the factory capacitance tolerance and have low ESR. So, I didn't change them. In general, the filter capacitors rarely fail in vintage gears, and I usually don't replace them unless their ESR is high.

Test results on the original filter capacitors:

C003: rated capacitance – 10000uF, measured – 10180uF, ESR – 0.22Ω, deviation: +2%
C004: rated capacitance – 10000uF, measured – 10140uF, ESR – 0.26Ω, deviation: +1%

Dial and Meter Lamps

The old incandescent lamps were replaced with warm white LED lamps to maintain the original look and decrease heat. The original incandescent lamps behind two meters were also replaced with warm white LED lamps. I have described this procedure many times in my previous posts (see for more details here). Note, that there is no vellum paper behind the dial scale in Marantz 2265B.

Dial scale removed - original incandescent dial lamps

Marantz 2265B_Dial Lamps_original

Dial scale removed - warm white LED lamps

Marantz 2265B_Dial Lamps_warm white LEDs

DC offset and Bias Adjustments

The DC offset on each channel is measured across speaker terminals (no load connected). It should be adjusted as close to zero volts as possible with the trimming resistors R710 and R760, respectively.

The bias is measured across two emitter resistors (wire wound type, 0.47Ω/5W). The voltage between pins J717 and J718 should be adjusted to ~20mV DC with the trimming resistor R716. This is a bias on the left channel. The voltage between pins J767 and J768 on the right channel should be adjusted to ~20mV DC with the trimming resistor R766.

DC offset on the left and right channels after restoration

Marantz 2265B_DC Offset_left channel

Marantz 2265B_DC Offset_right channel

Bias on the left and right channels after restoration

Marantz 2265B_Bias_left channel

Marantz 2265B_Bias_right channel

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 24.72 VRMS (left channel) and 25.06 VRMS (right channel). It corresponds to the output power of 76.4W on the left channel and 78.5W on the right channel.

Output power test

Marantz 2265B_Output Power Test

As usual, all the knobs and the face plate 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. Please watch a short demo video at the end of this post. Thank you for reading.

Marantz 2265B - after restoration

Marantz 2265B_after restoration

Marantz 2265B_after restoration_with old parts

Demo video after repair & restoration

Friday, April 26, 2024

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).

Allied Model 435_after restoration

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

Allied Model 435_Power Supply Board (W16-030)_before servicing

Allied Model 435_Power Supply Board (W16-030)_after servicing

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

Allied Model 435_Audio Unit (W15-043)_before servicing

Allied Model 435_Audio Unit (W15-043)_after servicing

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

Allied Model 435_Tuner Unit (W35-036)_before servicing

Allied Model 435_Tuner Unit (W35-036)_after servicing

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

Allied Model 435_Filter Cap C3_original

Allied Model 435_Filter Cap C3_new Nichicon LKG

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

Allied Model 435_Coupling Caps C9, C10_new Vishay

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

Allied Model 435_Dial Lamp_left_original

Allied Model 435_Dial Lamp_right_original

Allied Model 435_Dial Lamp_left_warm white LED

Allied Model 435_Dial Lamp_right_warm white LED

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

Allied Model 435_Dial Poiner Assembly_removed

Allied Model 435_Dial Poiner Assembly_new lamp installed

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

Allied Model 435_Stereo Indicator Lamp_original

Allied Model 435_Stereo Indicator Lamp_new

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

Allied Model 435_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

Allied Model 435_after restoration

Allied Model 435_after restoration_with old parts

Demo video after repair & restoration