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Audio Institute VR-70E - quiet,thin output left channel
Audio Institute VR-70E - quiet,thin output left channel
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Old 14th July 2018, 09:53 AM   #1
reliables2k is offline reliables2k  New Zealand
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Default Audio Institute VR-70E - quiet,thin output left channel

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
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Old 14th July 2018, 12:44 PM   #2
petertub is offline petertub  Sweden
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If within warranty period ; return it. Otherwize seek a qualifies repair man, could be

a ham operator, could be a serious hifi-shop .
schematics is available if needed.
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Old 14th July 2018, 03:55 PM   #3
Palustris is offline Palustris  United States
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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?
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Old 14th July 2018, 06:42 PM   #4
petertub is offline petertub  Sweden
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Default schematic vr70e

VR70E 2.pdf


Schematics
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Old 14th July 2018, 08:51 PM   #5
reliables2k is offline reliables2k  New Zealand
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Quote:
Originally Posted by Palustris View Post
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?
Quote:
Originally Posted by petertub View Post
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?
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Old 14th July 2018, 10:26 PM   #6
nigelwright7557 is offline nigelwright7557  United Kingdom
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If its old it could be aging electrolytics or degraded coupling capacitors.
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Old 14th July 2018, 10:41 PM   #7
reliables2k is offline reliables2k  New Zealand
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The sticker on the bottom says 2008 so is right around 10 years old.
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Old 16th July 2018, 11:39 AM   #8
6A3sUMMER is offline 6A3sUMMER  United States
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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.

Last edited by 6A3sUMMER; 16th July 2018 at 11:44 AM.
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Old 16th July 2018, 03:13 PM   #9
petertub is offline petertub  Sweden
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Yes, that is a design fault in all these. While you have it open, change 36k to 33k and be happy.
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Old 16th July 2018, 03:45 PM   #10
ErikdeBest is offline ErikdeBest  Switzerland
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Audio Institute VR-70E - quiet,thin output left channel
What voltages are you measuring over R26 and R28 (thr 10 ohm resistors)?
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