I thought a write up on this unit would be fun because theirs not a whole lot out there on the 2240, its a fairly limited production series manufactured in 1974 and you don't come across em' often like say the 2245 which is coming on the next posts, the 2240B appears to be available. The 2240 shares a similar phono stage to many of the lower wattage 22XX's series Marantz.
Power Supply P800
One nice little detail on this PCB is unlike the darker/maroon colored PCB's this seems to have a slicker surface and removing caustic glue is much easier! The relay was removed and contacts cleaned along with all new Panasonic FR/FC high temp (105C) long life capacitors which are ideal for switching/regulated power supplies. Also updated were the common cathode TO-220's @ H808/811. We'll be coming back to this board for regulated PS adjustments and DC offset adjustments after the coils. I am currently investigating the updating of the H801/802/803 BJT array used as a voltage regulator for maybe a LM packaged regulation, more to follow on this later….
Phono P400
Again, we've seen this topography on many of the Marantz receivers, their are a few components to notate, such as the failure and noise prone 2SC458 BJT's, which are replaced with Hfe matched 1845 transistors. Also updated is the glass pack diode and H409 to two 4148 diodes in series as you can see from the photo. Electrolytics were replaced with Elna Silmic II audio grades and a axial Nichicon TVX 220 microfarad capacitor along with quality ECW polypropylene at C414/415.
Tone/Pre-Amplifier PE01
I had some fun experimenting with different capacitor compliments in this stage and settled with audio grade Nichicon KA and Elna Silmics for electrolytics. Bi-Polar electrolytics were replaced with two ECW polypropylene 1microfarad film capacitors. The coupling stage CE01/2 were replaced with high quality audio grade Solen polypropylene capacitors as seen at the big black films. This board has the tone potentiometers attached so now is the best time to clean and lubricate all the phenolic controls here.
Errors evident on SM: Ce05/06 47/16 should be 4.7 & Ce21/22 33/50 should be 3.3
Drivers P700
Im always happy to see symmetric driver topographies on separate heatsinks and paths, its a sign up superior construction and quality. The electrolytics were replaced with audio grade Nichicon KA's and low impedance high reliability Nichicon PW's. Differential pair transistors at 701/702 were replaced with Hfe matched 992fbu's transistors. Its important to update differentials pairs, they often elude to significant noise issues prevalent in the driver stage, along with help maintain stabile DC parameters
AUDIO ADJUSTMENTS
REGULATED PS P800
-J804 und Boden @ R806 für 35Vdc
BIAS P700
-Emitterwiderstand punkte J708 und J710 beim R719 für 10mV
DC @ POST RELAY P800 und P700
-Links J809 und Boden 0>
-Recht J810 und Boden 0>
New mica and thermal compound applied and that finished up this stage, I do like to note if your not replacing the bias/offset potentiometers make sure you clean them at this stage with a good de-oxit and lubricant such as D-5 faderlube. I often leave these big white pots, I feel even the precision bourns available do not quite meet up to the robust solid design of these olders ones, if they track appropriately Id advise keeping them.
The direct coupled filter capacitors were replaced with 40mm 10,000 microfarad Panasonic THA capacitors with new sign terminals for easy installation.
RF und Hardware
Next we move onto the final RF stages which get all new low impedance high reliability Nichicon PW capacitors. New hardware and lighting and cleaning up the final shielding which about wraps up this 2240.
Looks good!
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