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Thread: Another humming problem!

  1. #21
    Join Date: Jul 2012

    Location: Wimborne

    Posts: 701
    I'm Alex.

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    I would say a wasp in a jam jar would be far too quiet and probably too high a pitch so lets go for humming!


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  2. #22
    Join Date: Jul 2012

    Location: Wimborne

    Posts: 701
    I'm Alex.

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    Quote Originally Posted by RothwellAudio View Post
    A hum could be caused by numerous things but just as an academic exercise I'll take a stab at it. My guess (and that's all it is) is that the hum is caused by excessive ripple on the power supply due to the voltage regulator having failed.
    The circuit is likely to be rather more sophisticated than a run-of-the-mill valve preamp so I'd get Glen Croft to take a look at it - he'll know the circuit better than anyone.
    It's certainly looking like that's going to be the plan of action. I just wished I discovered the problem sooner as I was up in Yorkshire all of last week so could've taken it up to Glenn.

    I guess I can still try and rule out a dodgy valve with the process provided by James, unless you think it's probably a waste of time and a valve is very unlikely to be the cause of my problem?

  3. #23
    Join Date: Apr 2012

    Location: London

    Posts: 685
    I'm James.

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    Hmm, just looked back to the original post. I had it in my mind that the hum was in one channel and thought heater:cathode leakage in a signal valve, but it seems it's in both, my bad, I must read more carefully next time. Apologies Alex. Given that the hum is in both channels and there are two sets of ECC83 that are probably not shared across both channels it becomes rather unlikely that two valves have failed, one on each side, simultaneously, so Andrews PSU option is more sensible. If you wish to play around then at least 85A2 valves are cheap and plentiful, they are almost always Mullard, and you can get them NOS from eg. Langrex, Billington and so on for about a fiver each plus postage.

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