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Old 12th September 2003, 03:12 AM   #11
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I am limited on transformers, which is why I ended up with this. Would it help if I connected the cathode to the negative 12V rail instead of ground?

The resistor in the heater supply was a 10-ohm.

I can add more caps... I'll see what goes.
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Old 12th September 2003, 04:29 AM   #12
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The hum is probably a combo of 60 and 120hz. Breadboarding is probably the culprit of the 60hz, but the supply is for the 120hz.

Since the tube will draw only a mill or so, you could add a 270 ohm, 1/2 watt and 100 uf cap to the plate supply and cathode supply, -12 volts, (after the IC is supplied voltage) with alot more suppression of the 120 hz ripple.

The distortion is caused by low voltage and improper resistances.

If you connect the cathode to the -12 vdc line, a small cap will need to be added between the grid and input jack. I would try increasing the plate current a little, if possible, by adjusting the plate and cathode resistances for the clearest sound. It may work or may not.

Hope this helps.
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Old 12th September 2003, 07:35 AM   #13
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Default Wire dropped off?

Where's the centre-tap on the transformer for the +/-12V supply? As you've shown it, the moment there's the slightest imbalance, your "earth" will wander all over the place and... ...cause hum.
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Old 12th September 2003, 08:07 PM   #14
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The center tap is grounded... I guess I forgot more things than I thought.

If I get some time, I'll try to mess around with values and voltages.
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