Pioneer SX-550 Receiver Highlight

Pioneer SX-550 Receiver

We have a little Pioneer SX-550 Receiver in today, thought we'd show some highlights. Produced for a limited run from 1977 to 77" its features a 3 gang tuning capacitor and modest 20W rated output. The 550 was the entry class for many SX users because of its price point.

Switch/Repair & Modification
One of the common issues with the lower series SX Pioneer's is the integrated Power/Speaker Selector switch. Both sections of the phenolic based speaker switch and integrated power switch are prone to excessive carbon build up and then AC arching. often presenting as fluctuating AC/ flicker lamps. If you place you ear near (*caution...) you can actually hear the arching.

One fix is to tear down the switch and phenolic assembly by desolder and removing the unit. As photo'd below its important to scour and clean the contact points and clean and treat with a high quality non residue cleaner.

In some cases, such as this.... no matter how much cleaning occurs the switch is done for.  In that case I recommend salvaging and cleaning the speaker selector and we did and adding a new power switch to the rear of the chassis for discrete mounting. A 5A DPDT single throw was chosen for this unit with a Vishay X1Y2 safety capacitor installed parallel the switch.

New multi-facet LED's were installed along with a LED function indicators. to give off a new clean/ white glow!

Audio Notiz
The resulting verification report was as expected with a slight deviation in the low frequency to sub-sonic frequency response at 10Hz to 35Hz with a noted deviation of +1dB.

Kenwood Model 600 Supreme Series

Kenwood Model 600 Supreme 

Here is another Kenwood Model 600 Supreme we have in for a restoration. The Kenwood 600 is a TOTL variant quietly produced and exported by kenwood-trio. part of the infamous Supreme series, manufactured from 1973 to 1979’ this features the popular dual power supply topography designed by kenwood and later adopted with Kentronics which later produced the Accuphase series. From research it would indicate that their are potentially less than the 1500 or so 600’s out there produced and who knows how many left in good repair.

With an impressive 18,000MFD of filter a side for a total of 72,000MFD of reserve!, the 600 also touts a limited ALPS 44 stepped attenuator and a ALPS coaxial balance fader! The 600 used excessive heatsink platforms and specific shielding channels for input/output leads along with bottom chassis well.

Power Supply X00-1720-10 & Protection X00-1700-20

The dual mono power supply assembly is a slide connected PCB into a molex base at the chassis, supplied with independent 18,000MFD caps.  The electrolytic were all replaced with a high temp (105C) long life Nichicon PW and Panasonic FR/FC type with VP 100MFD bi polar capacitors.

Through several variations I was able to correct the 40/28 and 14V output voltages by updating the 2sc1419/2sa755 BJT’s to heavy duty On Semi MJ15/32/33 type TO-220 transistors along with their TO-92 pairs of KSA992/KSC1845 type. 

BEFORE

Noted dZ5-9 were updated to general type 1N4148 diodes and the V06B type diode at Dz10 updated to a ultra-fast 4005 type diode. I want to also note that the glue used for the large original 100MFD caps had severally corroded the diode at Dz10 and associated resistors which had to be replaced.

AFTER

The ProtectionPCB is a dual facet over current detection and excessive offset detection.  Protection transistors Q9-11 were all updated to 733/1845 BJT’s. I want to note that pinout for Qz9/10 (733/1845) are different than the PCB topography. Qz11 was updated to a KSC6909AYS class (2SD415) and a new Omron MY2-24V was installed.

The original four 18,000MFD filter capacitors were replaced with a high quality Nippon Chem-Con 18K 75V filter capacitors with adapted screw terminations.

Originals...

New Nippon 18Kmfd

Amplifier Stages X07-1440-00

The driver stage consists of an initial 1st order dual FET package IC differential 2SK58, which is enclosed in its own shielding!, the proceeding second stage differential is comprised of a pair of NPN transistors (front end gain bump). The 2nd order differential were swapped with 1% matched ZTX694 bjt’s (All BJT’s watch pinout*) and 3rd order differentiate KSA1381 type. Major upgrades to the transistor packages should be done as we did here due to their high failure rate at Q6 (2sc1452) to a KSC3503 for the constant current BJT.

All the original bias and especially the offset course/fine post should be replaced, we choose a high quality Bourns precisions multi turn trimmer. All the electrolytic capacitors were replaced with a audio grade  Nichicon KA (10MFD) the remaining films were replaced with a high grade WIMA polypropylene .1MFD and a Panasonic ECW high grade polypropylene .01MFD capacitors. One of the prized components in the driver stage is the TO-3s were Sanken 1164/747A output devices capable of a 40A drive(PVP)!, which were removed and MICA/compound applied.

Pre-Amplifier (RIAA) X08-1560-10, Tone Control X11-1310-00 & Filter Assembly X12-1130-10

Unique to the technilogical advances prevalent within the 600, the RIAA stage is comprised entirely of  JFET devices. In a 3rd order array the initial FET’s comprise of a Class A differential + drive stage with a constant current regulation.  All the original electrolytic were replaced with audio grade Nichicon KA and Fine-Gold capacitors, while 1MFD< were replaced with high grade WIMA polypropylene film capacitors. 

The tone stage is designed again around a class front end, using a Shunt-Regulated-Push-Pull (SRPP) configuration using  FET’s. (2SK Japanese devices) The Tone and filter assemblies were treated as above, with all electrolytics replaced with audio grade Nichicon KA and high grade WIMA polypropylene film capacitors. The input stage of the filter assembly had the original mylar/poly films upgrade to high grade Panasonic ECW polypropylene type. 

Verification Report 4/8 OHM Reports

Marantz 2230 Receiver Restoration

Marantz 2230 Receiver 

Today were showcasing another Marantz 2230 Receiver restoration! One of my absolute favorite Marantz receivers with looks to go, the Bleu LED’s we install in these turn out phenomenal. 

"Best in its class. With impressive specifications and Marantz-exclusive features, the Model 2230 offers more value and performance than any other receiver in its class. We've known that for years. But just recently, one of the nation's most respected independent consumer testing organizations verified it. In not one, but two separate categories -- featuresand performance. It delivers 60 Watts continuous power, both channels driven, from 20 Hz to 20 kHz with total harmonic and inter-modulation distortion well under 0.5%. Stepped, three-zone tone controls for BASS, MID, TREBLE. Provisions for tape decks, phones, record changers and 4-channel adaptors. Ultra low-distortion FET, RF and IF circuitry. Massive heat sinks; automatic protection for internal circuitry and associated speakers, plus the famous Marantz gold-anodized front panel. Looking for a moderately priced receiver? The Marantz 2230 out-does them all."

- excerpted from a 1973 Marantz stereo equipment catalog

Power Supply P800

The regulated 30V power supply is a simple design supplying 66V rails for the drivers and 14/35.6V for the auxiliary assemblies.  All of the electrolytic capacitors were replaced with a high temp (105C) long life Panasonic FR/FC capacitor, The original 2SC1213 NPN transistor was replaced with a modern TO-92L KSC2383 BJT along with the 14V /500mW zener at H806. The mounting glue is etched off as well, the noted 30V TP is at J808. The original filter capacitor was upgraded to a low ESR long life 10,000MFD capacitor and both coupling capacitors upgraded to two low ESR, long life 6800MFD capacitors. A new 7A DPDT power switch and Vishay X1Y2 safety capacitor was installed as well.

P400 Pre-Amplifier

I decided to try some very nice Solen polypropylenes on this stage and the phono to replace with original polypropylene films. I think the the MPK Solen is an incredibly film, cost appropriate yet ever bit as good as the EVO Oil’s we’ve tried extensively.   The remaining electrolytic were replaced with audio grade Nichicon KA/ Fine-Gold series. Per our protocol all 1MFD (AF) stage caps were replaced with a high grade WIMA polypropylene film capacitor. The P400 is designed around a small signal BJT complimentary gain driver stage with variable bass/mid/high attenuations. This same topography is seen in MANY of the 22XX series such as the 2245/70.

BEFORE

AFTER

P700 RIAA/PHONO

The phono stage is in the 2230 is one of the best, bar none. With a nominal Av of 40dB its more than enough drive. Their are some major updates this assembly needs though. The notorious 2SC458 transistors are well known to break down under load with pre-emptive failure and potential noise floor issues, these were replaced with 1% matched Hfe 1845 BJT’s. The original tantalums were replaced with a audio grade Nichicon KA capacitor and Fine Gold 100MFD Nichicon. The original films were again replaced with a high grade Solen MPK polypropylene film capacitors. The original VD glass pack diodes were also replaced with tH709 constructed of two 4148 diodes in series and 708/707H single 1N4148 diodes. 

P750 Driver Assembly

I’ve always been a huge fan of the 2230 topography, very simply push-pull design thats tried and true, very stabile and reliable unlike the 2270. Using a single H751 as a gain drivers to the H752 down to the 3rd order devices. It employs a integrated current limiting protection of the output devices through a current deviation circuit.

All the electorlytics above 1MFD were replaced with a audio grade Nichicon KA and Fine Gold, the 1MFD pre-driver coupling capacitor was replaced with a high grade WIMA polypropylene film capacitors along with a 100PF  WIMA polypropylene at the input capacitor C761. The output coupling C760 .1 MFD film was replaced with a high grade MKS PP WIMA film capacitor as well.  Both Bias and clipping potentiometers were replaced with precision tolerance Bourns pots. new thermal compound was applied to the outputs and thermal tracking diode H005 SV-3A. Its very important to update the glass pack at H757 S3016R with a general 4148 diode for reliability. 

I want to take a special focus on the before and after verification reports, the results are tremendous! Lowered total THD+N response, more linear frequency response at the peak sub sonic and ultra high frequencies, about 3 watts gained with an even better intermodulation response (4:1 60hz/7Khz)

BEFORE Restoration

AFTER Restoration

Marantz Model 22 Receiver Duo Rebuilds

Marantz Model 22 Receiver

I wanted to showcase two Marantz Model 22 receivers that came in for restoration. Manufactured from 1969 to a last run of 1972, their are two version, one revised and the early models.  Rated at 40/W over 8 ohms.  The Model 22 is an excellent sounding early Marantz receiver pre-dating the 22XX series runs. The Model 22 tends to be a very extensive rebuild as it hosts an array of the 2SC458 transistors which are very failure and noise prone BJT devices. Along with a plethora of service updates and bulletins. 

P800 Power Supply & P980 Speaker Protection

The Model 22 has an interesting design for the power supply. using a dual configuration supplying a 27/35V rails for the tone/phono and driver + driver stage and a 12V rail tap for the RF and differential front end driver sections. 

The original topography used two large metal 1000/MFD 50V can capacitors which were replaced with a 10mm leaded high temp (105C) low impedance Nichicon PW capacitors. The remaining electrolytics were replaced with high temp (105C) low impedance Nichicon PW and Panasonic FR/FC capacitors. The section bridge rectifier bypass with .01/MFD Panasonic ECW film capacitors. 

The original RF front end H801 BJT 2SD324 was replaced with a 2073NPN BJT. I do want to note that H801 pinout is different on the unrevised and revised versions.  Pinout of this TO-220 is typically BCE. On the unrevised model the pinout is ECB so the TO-220 was mounted under the chassis with a new MICA insulator, this is better than cropping the legs to the correct BCE, just transposed the BJT. Both H803/804 2SC734 BJT’s were replaced with 1845 NPN BJT devices and H805/806 1S332 diodes replaced with a 7.5Vfd diode. Note the output difference for the two model at J805 of 35 and 27Vdc.  The two 4700MFD 50V filtering capacitors were replaced with a low ESR Panasonic THA 5600MFD capacitors with a low profile to help keep the surface down from heat.

P980 

The speaker protection PCB is located under the P800 assembly. Their are two very different topographies used between the two Model 22 versions. The revised version omitted the flyback diode arrays H984/985 for some reason, which is added back with a Utra Fast 4005 diode cathode at J983 and anode to J984.   The problematic 2SC984 metal transistor seen on the later 2270 mods is replaced with a more reliable MJE243 BJT device and H981 2SC828 updated to a 1845 NPN BJT device.  All the electrolytic were replaced with a high temp (105C) low impedance Nichicon PW capacitor.

The older LY relay was mounted under the chassis to a L bracket near the output inductors. I actually havent come across this mount but on these 2# series Marantz, they tack the relay with a screw through the bottom threshold.  I replaced the original my a 24V Low Noise Omron MY2 relay, fixed with a plastic safe epoxy to the bracket.

P700 DC/FM Amplifier Assembly

Again, similar to the P980 assembly their are two versions of the P700 PCB. One with a BJT network and one version consisting of a 4 NPN driver configuration.  All of the electrolytics here were replaced with a audio grade Nichicon KA capacitors and the original .22MFD mylar films replaced with a high quality WIMA polypropylene film capacitor.  The original H705/706 were noted to be the problematic 2SC458 devices, which were replaced with matched 1845 NPN BJT’s along with H707/708 2SA494 with complimentary KSA992 BJT’s. H709 was replaced with a general 4148 diode.

P400 Tone/Pre Amp & P300 RIAA (PHONO)

The pre-amplifier topography reminds me of what we see in the 1030/1060, 2230+ Marantz. A very simple, musical symmetric topography. I love this design. Employees with a NPN front end gain stage and variable RC feedback design.

The original mylar .22MFD input coupling films were replaced with two high quality .22MFD WIMA polypropylene film capacitors. Due to their footprint some mounting modifications had to be integrated.  High grade WIMA polypropylene were also used for the output 1MFD capacitors. All remaining 100/22/2.2MFD electrolytics were replaced with a audio grade Nichicon KA capacitor. The P400 assembly again uses the problematic 2SC458 BJT device at H401/402 which were replaced with 1845 NPN BJT devices. Due to the high rate of issues within the Model 22 pre-amp the remaining BJT’s were updated as well with KSA992/KSC1845 low signal BJT devices. 

P300 RIAA

The phono stage in any Marantz is superb after some TLC, some of the best I know, the documented RIAA response is damn near flat on the Model 22. Impressive stage.

The original 1MFD electrolytics were replaced again with high grade WIMA polypropylene film capacitors and remaining electroyltyics with Nichicon Fine Gold and KA capacitors.  This is one of the few RIAA marantz stages without the 2SC458 or glass pack VD diodes which is nice to see. 

P600 Power Amplifier 

The Model 22 driver section is a push-pull symmetric single pcbs assembly, with the exception of the input its a direct coupled design utilizing a degenerative feedback array. The P600 uses a TO-99 differential amplifier IC for the initial gain stage versus a pair of differential pair TO-92’s thermally coupled. The MC1741 is updated with a LM741 package available in a TO-99 or DIP8 device.

LM741 Block Diagram

Input films at C601/602 were replaced with a high quality Solen MPK film capacitor. All the electroylytics here were replaced with a Nichicon Fine Gold 100MFD capacitor. Signal path mylar’s were removed and replaced with a high grade WIMA polypropylene film capacitor along with the output .22MFD capacitor with a footprint modification at the output pins. 

Bias punkten 

J606/608 for 10mV beim R961

J607/609 fur 10mV beim R962

RF Stage

The remaining AM/FM PCB assemblies had their respective capacitors replaced with a low impedance high temp (105C) Nichicon PW capacitor along with two 220MFD capacitors foil side. The dual AM/FM tuning capacitors were cleaned with 99.999% anhydrous alcohol and dusted. 

LED Lamping

New Led’s were installed at the meters and dial display. These were hand-made using the original BA9S bulb bases. By heating the metal base you can separate the glass bulb and remove the original filaments, leaving just enough room for diode/resistor.

Audio Notizen

Still graphing our response but initial results look great.  

500Hz 19.14Vrms (45.79W/Ch @ .057%dB THD+N

1000Hz 19.14Vrms (45.79W/Ch @ .059%dB THD+N

10000Hz @ .059% THD+N

Still graphing but response is well within spec