Hacker Constellation Amplifier

[Ultrasheep]

My first post and seeking some advice please. I have a Hacker Constellation radiogram which has a separate amplifier for each speaker. Currently there appears to be a problem with the amplifier for the right hand (as you look at the front of the radiogram) amplifier. There is plenty of volume from the left hand speaker but very little from the right. I have put the leads from the right hand speaker to the left hand amplifier and they work fine. This is what has lead me to believe that the amplifier is the problem. There is a capacitor across the speaker connections which doesn’t look well to me. Is this likely to be the problem? Thanks in advance for any help/advice.

[Herald1360]

That looks like a bit of a mess- especially the LH? (working) amplifier.


According to to service manual (available from the Yahoo Hacker Audio Group, free to join), there's no capacitor across the speaker connections.


Yes the pictured capacitor looks a bit sorry for itself, but whether it has any bearing on the fault.......? There's a lot of other potentially dodgy components there as well.



Do you have and understand the use of any test equipment (multimeter etc) and soldering ability? There's a table of expected voltages in the A203 amplifiers- if this means anything to you it would be helpful to check them and report back here. If it doesn't this process could get very tortuous.



Although these amps are relatively straightforward designs, they are directly coupled which means that diagnosing faults can get frustrating since a problem in one component can upset or damage others and it can be difficult to see what is cause and what is effect!


Anyway, let us know where you stand and we'll try to take it from there.

[Nuvistor]

I cannot see that capacitor in the circuit, do both channels have one connected across the speaker?
You need to do some fault finding and testing before jumping to conclusions, the capacitor could be causing a problem but without knowing more about its position in the circuit it’s impossible to tell.

Crossed post with Chris

[Ultrasheep]

Thanks for the quick replies. I have joined the Yahoo group and printed off the manual. I have a multimeter. When looking at the static voltages that need to be measured would I be correct to think that the first letter given (from c, b and e) would be where I would connect the ground connection of my meter? Do I need to also measure the Ic values? If so, please could you advise how I would do so.

[Station X]

c, b and e indicate collector, base and emitter. Unless otherwise stated it's usual to measure voltages with respect to (wrt) the negative supply line. So you'd connect the negative lead of your meter to the negative supply line and probe c, b and e with the positive lead of the meter.

[Nuvistor]

Hi Ultrasheep,

You need to read the manual carefully, some voltage reading are with respect to earth, they usually mean chassis, and some are the voltages vbe, vce etc, also note the last page of part 2 which show modifications to the output stage where germanium transistors are substituted for silicon and the voltages are different, there is a table of the voltages on the last page.

There is also a warning about not running the amp with only one output stage connected unless the power supply has a suitable load, it can damage parts.

[Ultrasheep]

Thank you for your help. I am hoping to carry out the checks in the next day or two. I’d appreciate any advice as to the safest/best way to carry them out. This isn’t something that I have done before.

[Nuvistor]

Don’t short anything out with the meter probes, if they the type with bare metal end about 1cm long wrap some tape around then to just leave a bare point at the end.

Areas of the machine, mains input, on/off switch, transformer etc keep away from those.

[Ultrasheep]

Thank you. I’ll let you know how I get on.