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Friday
Mar082013

Which lamp works well for Marantz Models 1200 and 1200B

When it comes time to replace the pilot lamp in a Marantz model 1200 or 1200B which is the right bulb to use?

The service manual does not specify any lamp number and the parts list just shows a Marantz part number.  Unlike many other models, there isn't a lamp number printed on the rear panel of the amplifier.

I have seen many suggestions for different miniature lamps, most of which are probably worng.

In a 1200 or 1200B the pilot lamp is powered through resistor R711, which is a 220 ohm 2 watt resistor.  When inspecting this resistor on these models, I ususally find that the resistor show signs of heat stress from way to much current flowing through them.

The heat stress is of course bad for the resistor and also for the board where it is mounted.  When replacing this resistor, it should be mounted up off the circuit board about 3/8" to allow for better air flow around the resistor.

The lamp circuit supplies 51 volts DC to the empty lamp socket.  The goal when choosing a lamp is to find the correct style of lamp with the correct voltage and current rating for the application.

After researching miniature lamps I decided to use a Chicago Miniature Lamp #1835.  The 1835 is rated for 55 volts at .05 amps.  This means that the filiment resistance is 1100 ohms.  This lamp should use only 0.23 watts of current through R711, which is nothing for a 2 watt resistor.

After installing the 1835 into my completed model 1200B I found my choice in using the 1835 seems right.  R711 now runs cool as it should.

 

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