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Cornet octal point-to-point build hum

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6L6GTR

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Cornet octal point-to-point build hum
« on: 2 Jun 2016, 04:43 pm »
Hello,
I just finished up a Cornet Octal with point to point wiring as my first DIY audio project from schematics, but there's a slight issue with 60 hz hum on both channels with inputs shorted.  It's not loud but it's noticeable during "softer" music at listening position. 

I made a fairly accurate diagram of my build to illustrate my wiring.  All wire is 22 ga solid copper except for the PT and safety ground.  I'm not convinced that my supply grounding is proper...  Does anything stand out?  Thanks in advance for any help!

Bigger pic: http://i.imgur.com/u8pDvxe.jpg





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Folsom

Re: Cornet octal point-to-point build hum
« Reply #1 on: 2 Jun 2016, 08:41 pm »
Check resistance from IC tabs to chassis. That is if any of the legs are connected to tab. Plus it might help if they're isolated period.
« Last Edit: 3 Jun 2016, 03:31 am by Folsom »
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6L6GTR

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Re: Cornet octal point-to-point build hum
« Reply #2 on: 4 Jun 2016, 01:42 am »
The tabs of the CCS transistors (TIP50) short to collector, but they're mounted with insulators and plastic shoulder washers.  I've verified there's no continuity between the tabs and chassis. 
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G Georgopoulos

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Re: Cornet octal point-to-point build hum
« Reply #3 on: 4 Jun 2016, 02:02 am »
power supply filter caps are inadequate...cheers... :)
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6L6GTR

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Re: Cornet octal point-to-point build hum
« Reply #4 on: 15 Jun 2016, 03:31 pm »
It turned out my tubes were leaky.  I managed to pick up some 5691/5692's that made it run silently.  R21 was lowered to maintain 6.3v. 
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