• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Audio Institute VR-70E - quiet,thin output left channel

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A wee while ago I purchased a Audio Institute VR-70E made buy the Affordable Valve Company.

Just today I turned it on an noticed the left hand channel was very quiet and thin sounding when compared to the right hand channel. I would approximate half the volume.

I have done some basic troubleshooting, switched inputs left to right, speakers left to right, and valves left to right. In all scenarios the issue remained with the amplifiers left channel output.

I live in a small town and do not have easy access to someone who could look at this, so i'm hoping someone here can help me diagnose and possibly repair this amplifier, while I have a basic understanding of electronics I really need some help here as this is the first time I've had to troubleshoot a valve amplifier.


Many thanks in advance
 
Have you got a schematic and DMM? Are you comfortable checking voltages with the unit powered on and comparing them with expected voltages on the schematic?


Thanks for the quick responses :)

Thanks to 'Petertub' I now have a schematic, and yes very comfortable with checking voltages while the unit turned on.

Palustris: Where do I take these measurements?

Also it maybe worth noting that when turning off the Amplifier a small pop comes from the lefthand channel speaker - perhaps this is a helpful piece of information?
 
looking at the schematic:
Is the second tube supposed to be a concertina splitter?
It seems to have a 36k resistor in the cathode, and the plate resistor seems to be at "C"
33k resistor on the power supply section of the schematic.
33k does not equal 36k, that is an unbalanced concertina.
It is very early in the morning here, it is too hard for me to "trace" it all out.
 
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