Vintage receiver restorations

I've got the bug for nice vintage gear at the moment, so on the back of the recent AR loudspeaker rebuild decided to get working on a couple of receivers - a Marantz 2225 from 1977 and a Pioneer SX-737 from 1975. I just love the look of these old 70s receivers, the blue dials and meters, the deep red indicators, the contrasting black/silver faceplates and the chunky build.

I've had the pioneer for a few years and other than a clean of the switches it's been untouched. It's now had a full rebuild but this thread will concentrate on the latest arrival which is the Marantz. These 70s Marantz units are currently quite popular and seem to command quite high prices. In the US market the 2200 series can often go for $300+ even for low power model, much more if restored.

They are exceptionally well built by any standards but especially for what were relatively mass market bits of kit. Heavy metal chassis and controls, proper heavy duty wafer switches, good firm and smooth acting controls and very neat internal layout. The power amp in this series use direct coupled outputs, while those very similar looking models from the early 70s used capacitor coupling. There are many models to chose from but I prefer those such as the 2225 which have the larger black area on the front - it contrasts nicely with the silver buttons. The really unusual feature on these receivers is the three band tone control, so you get a 'mid' control alongside the regular bass and treble. It's action is sensibly curtailed to +/- 6dB.

This particular sample was working but had the usual crackly switches and pots and most of the dial lamps were blown. The latter consist of seven 250ma fuse type lamps, plus two further lamps for the stereo indicator and dial pointers. That's quite as lot of heat and 2A of current. For the moment I've replaced the dial lamps with original style fuse lamps of the same rating, but I've got a set of fuse lamps fitted with high brightness multiple SMD leds arriving soon, so we'll see how those compare. They'll certainly dramatically reduce the current draw and the heat.

40 years or dust and grime had settled inside as you can see from the pics below. Fortunately no water/humudity damage and this example appears to be absolutely untouched. The dial and meters are backed with vellum diffuser paper and this goes brown with age, turning the display a muddy green instead of the crisp blue intended. Fresh vellum paper soon sorted that.

Other than stripping and cleaning the beast, all boards were recapped and also some sad looking carbon resistors replaced in the PSU with higher rated types. Any bipolar signal caps have been replaced with either panasonic or wima film caps while the good old Panasonic FC has been used for everything else bar the main filter caps which have been bumped from 6800/50v to 10000 at 63v. The smaller PSU caps for the pre and tuner sections have also received a bump in capacitance and voltage rating - but nothing too extreme. The phono board is surprisingly nice and is a three stage design - very sensitive and quiet. This already used good quality film caps of close tolerance which was nice to see.

I've already converted the dial pointer to use a high bright red led. This originally used a lamp running on 6.8v ac. Just take a 3mm red led, snip the leads up tight, attach a tiny IN4148 diode on one leg and a 680R resistor on the other. Heat shrink the lot and it fits neatly into the original lamp space. You'll get 3.3v dirty dc now at the led terminals. No deed to start bolting rectifiers and caps to the chassis just for the lamps as I see done in some cases. Too much faff and it looks horrible!

Other than all switches and pots cleaned with Deoxit and Faderlube, bias and dc voltages set - that's it. Nice to see good temp compensation on the power amp board. Both drivers and output devices have feedback diodes for stability and once the quiescent current hit the target after about 90 seconds, it stays there.

I don't do subjective comments on 'competent' amplifiers so 'it sounds absolutely lovely and I can hear nothing amiss' will have to do

The 2225 is rated at 25w rms and this one clips at 33w - so the usual conservative rating but this is no powerhouse. Fine with normal 86-89dbw loudspeakers if you avoid headbanging levels and perfect for anything higher if you don't. Just don't expect it to drive Magneplanars or Apogees.....



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After:




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.... the lights are more blue in real life and the red lamps less pink than the camera shots.

 

A lot of work there, Rob. In those days they certainly put a lot a material and effort into their products.

 

I had no idea it was that grubby when you got it. I appreciate the way it looks now! Like new

How did you clean the circuit boards? Did you wire brush the chassis?

Loudness button too..

 

This range has a very well ventilated top cover so lots of open slats which of course is nice for temperature but has allowed 40 years of shite to be sucked in.

Natural bristle pointed paint brushes, compressed air cleaner, mini vac and some industrial cleaning wipes with lemon juice
Outer finished parts, knobs and levers etc + glass and plastics get cleaned with foaming cleaner of the sort used for cleaning printers and computer hardware.

Outer paintwork always looks great with a wipe over and buff with WD40 - but that's a trade secret so don't tell anyone. Works fantastic on those rough textured Naim cases too when applied with a paint pad

 

Lovely work Rob!

My Dad has a Rotel RX-503 which hasn't been used for years. It is tidy and all there.

Do you know anything about that model?

 

Cheers, it's belting out Bob Marley nice and loud at the moment and driving statics without smoke or the clatter of relays
The phono section is very low noise and clean. The MM input is even useable with a 0.4mv AT MC without obvious hiss or hum.

That Rotel should be very nice. It's from their mid-upper end and since the amps and tuners were well regarded the pairing in one chassis should make a good unit.
If you restore it, be warned as the results might surprise. You might end up like me and largely give up on modern kit. Digital/DSP and convenience aspects aside I can see little benefit to modern hi-fi kit in terms of sonics.

Retrive it from wherever it's resting and get cracking on it

 

Nice work Rob.

 

Rob,

You'll like this: http://select45rpm.com/pages/hifi/top-amps.html

 

Outstanding job on Marantz restore and like the method of using the 3mm led for dial pointer.Did you use a ultrasonic washer for the boards?

 

Beautiful job. At least it looks wonderful, and I bet it sounds the same.

I lusted over those receivers - especially the blue lighting and the "gyro-touch tuning"!