Sunday, September 4, 2016

Marantz 2250B Receiver W/ BA312 Upgrade and Restoration

Marantz 2250B Receiver 
**UPDATED 12/09/17 Customer sent back for installation of new Analog Esoteric BA312 Upgrade on the PE01 stage highlighted below**

Today were showcasing a Marantz 2250B Receiver.  With a limited production run starting in 1976 the B variant featured the optional Dolby package.   The 2250B reminds me a lot of the smaller 22XX series and how their built in comparison to the 70W/Ch chassis’s. 

P800 Regulated Power Supply
The regulated power supply like the 23XX and some 22XX series features a onsite relay and regulating TO-220 331/330 35/14V regulating circuit. The electrolytic capacitors were replaced with high temp (105C) PW Nichicon and high temp long life Panasonic FC capacitors.  The 3 legged common cathode diodes were replaced with TO-220 MUR1620 type diodes along with the 2471/WZ diodes.

After P800 the power switch was replaced with a 7A DPDT type and a Vishay X1Y2 Safety capacitor.  The direct coupled 10,000/50V filter capacitors were upgraded to 12,000MFD/80V capacitors. At this time new SMD LED’s were installed and a PW Nichicon for the metered 33MFD capacitor along with a new Dial pointer LED and Ferrite Antenna Bracket per order. 

PE01 Pre-Amp
The low distortion pre-amplifier in the 2250B  uses a common pre-amp IC consisting of a darlington type class A gain stage called the BA312 DIP7 package.  I will say this comparing our verification report...this has one of the best frequency responses achieved yet on a 22XX series Marantz!

**UPDATED 12/09/17 Customer sent back for installation of new Analog Esoteric BA312 Adaptive Module Upgrade on the his PE01 stage highlighted below, check the link below for product information!**

Also the glue for the original 220/35V electrolytic coats the BA312 resistor network which is removed, glue stripped and new 1/4W metal film resistors installed, the associated  IC buffer caps were replaced with low impedance Nichicon PW’s. Input films were replaced with high grade MKP polypropylene film capacitors. Remaining tantalum and electrolytic were replaced with audio grade KA Nichicon’s, VP BP and high grade WIMA polypropylene film capacitors. 

This phono stage is used in most 22XX series Marantz with some variations on the axial capacitor.  As discussed before, the 2SC458 BJT’s must be replaced in matched pairs due to their tendency to breakdown and cause noise.  Matched 1% 1845 BJT’s were installed, as well as 4148 replacing the 2473 diodes The original glass pack/epoxy VD1212 diode was replaced with two 4148 in series.  The axial was replaced with a 220MFD TVX nichicon and KA audio grade electrolytics installed. WIMA polypropylene capacitors replaced the original tantalum caps.

Here is the only published RIAA Curve Response online to date we tested and compiled

Drivers P700
 This is one of my favorite parts of the 22XX and 2250B receivers. The incorporation of separate, cap coupled driver PCB’s, the left channel uses a  isolated shield against the RF PCB’s.

  The differential pair transistors were replaced with 1% matched  992’ BJT’s and pre drivers 710/711H updated with modern 945/733 BJT’s. All the MV-13 epoxy diodes were replaced with series 4148 diodes. Ive discussed before the benefits of the large white plastic trimmers, the originals were pulled, tracked, cleaned and lubricated and re-installed after confirmation of tracking again.  Each TO-3 was pulled and refreshed.  Several noted 1/2W resistors were replaced due to thermal compensation.  All of the electrolytic were replaced with audio grade KA and low impedance high temp (105C) PW’s.

RF Stages
Recapping the RF stages is often the most time consuming part of any restoration due to the population of tantalum and electrolytic capacitors. 

Each stage was opened and all electrolytic and tantalum capacitors were replaced with Nichcon PW capacitors. Values at/under .22-.47 were replaced with Panasonic ECQ stacked film capacitors. 

Audio Notizen

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