Beomaster 4400 Type 2417 - Australia Project - Initial Checks

Here is a really nice example of a Beomaster 4400 Type 2417 receiver.

This one has been sitting patiently in my backlog of Bang & Olufsen restoration projects for a while.

It is the first Type 2417 unit I have seen.  All of my other Beomaster 4400 restorations have been Type 2419 units.

The Beomaster 4400 Type 2419 receivers have a transformer for the US market.  Their transformer is for 117 V, 60 Hz and has two switched AC outlets in the back for connecting other audio components.  I never liked having those switched AC outlets as it means more current through the Beomaster 4400 receiver's power switch when it is turned on.

The Beomaster 4400 Type 2417 does not have any additional AC outlets and it has a voltage selector switch so the transformer can be configured for markets that have AC voltages of 110 V to 240 V. 
Much nicer.

Like so many of the Beomaster 4400 receiver cabinets, the four rubber feet are worn down and there is corrosion around where they mount to the bottom, metal plate.  I will have to replace those and clean off the rust.

The procedure to open the top of the Beomaster 4400 cabinet for access to the internal components is pretty easy.
Two screws need to be loosened in order to move two cabinet latches out of the way.
Four screws have to be removed to allow the wooden cabinet to slide back and up for removal.
A couple of those screws are partially hidden by Beomaster 4400 heat sinks.

With the cabinet opened up I am pleased to see that the internal components look like they are the original factory components.

This photo shows the space between the Beomaster 4400 voltage selection and the transformer.
In the Type 2419 units, this space is crammed with the wiring for the two switched AC outlets.

Normally I jump straight to cleaning and replacing the electrolytic capacitors.

This time I decide to try some basic testing on the Beomaster 4400.

The first thing I did was to check the no-load bias current per the service manual.
Both channels (Left & Right) were low so I adjusted them to about 10mVrms across their respective emitter resistors.

Next, I set up my audio tester.
As in other Beolover Blog posts where I test my restored Beomaster amplifiers, I am using my two 8.1 ohms dummy loads for the speakers.

These dummy loads are made up of a 4 ohms resistor + a 0.08 ohms sensing resistor + a 2 ohms resistor + a second 2 ohms resistor.  In series these measure 8.1 ohms.

The different resistor segments allow me choices of where to place my differential measurement probes to measure the power/frequency/distortion of the output amplifier.  My QuantAsylum QA401 Audio Analyzer can only handle a maximum of 26 dBV (50 W across an 8 ohms load) so the resistor segments let me choose a measurement point that is friendlier to the analyzer. 

In the case where I was going to measure 50 Watts out of the amplifier across my 8.1 ohms dummy load, I would place my differential probes across the 2 ohms sensing resistor of my dummy load.
The maximum dBV across the 2 ohms resistor for the 50 Watts output would be around 14 dBV.

On this pre-testing of the Beomaster 4400 Type 2417 output amplifier, I don't expect to get to a very high output.

The output of the Audio Analyzer uses two single-ended signals for the Left channel and the Right channel.  I typically connect them to the Tape 1 or Tape 2 source input.  The most common test signal I use is a 1kHz sine wave of 0.316 Vrms.

This photo shows the test connections underneath the Beomaster 4400 cabinet.

For my initial testing of the Beomaster 4400 Type 2417 I started with the volume at zero and observed the distortion measurement as I increased the output across the dummy load resistors to 1 W.

The THD measurement was surprisingly good at 1 Watt output from the amplifier.

Things went bad for the Right channel when the output amplifier went just past 7 Watts.

Here is what the workbench looks like during the audio analyzer testing.

So a bit of pre-restoration testing just to have as a reference when the restoration is complete.

My next task is to begin moving/removing some of the Beomaster 4400 internal components to make way for the electrolytic capacitor replacement.  I will also change the trimmer resistors in the amplifier section and rework the thermal insulation of the transistors on the Beomaster 4400 heat sinks.

There are also some transistors on the main PCB of the Beomaster 4400 that get really hot.  I will look at attaching some thermal protection to them as well.

As I do on all of the Beomaster 4400 restorations I work on, I will install an arc suppression device for the power switch.