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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all products

4 posters

    SP14 hum during warmup


    Posts : 19
    Join date : 2021-02-12

    SP14 hum during warmup Empty SP14 hum during warmup

    Post by bobgroger Sat Jul 17, 2021 9:53 pm

    I know you are supposed to turn the preamp on and warm it up before turning on the amp. BUT... I have a 120 hz hum during warmup that seems to be very dependent on tubes and their locations. In all cases the hum is gone when warmed up, not the noise with some tubes. I have 10 old stock 6SN7 tubes. Some are microphonic. Some hum worse than others. Some are noisy. Are new manufacture tubes any better?

    Posts : 148
    Join date : 2017-08-10
    Location : MetroWest, MA

    SP14 hum during warmup Empty Re: SP14 hum during warmup

    Post by DavidR Tue Jul 27, 2021 2:00 pm

    Some new production tubes are OK. My beef with them is that they do not sound toobie/warm. Remember, Russia and Yugoslavia (or whatever the other country is) are not the pinnacle of production/manufacture. China is the other source with cheap tubes. However, you can get some nice tubes, like Psvane, but you pay the price.

    Posts : 1713
    Join date : 2008-11-30

    SP14 hum during warmup Empty Re: SP14 hum during warmup

    Post by tubes4hifi Thu Aug 05, 2021 7:11 pm

    tubes rarely have hum, you must have some very old, very bad batch of tubes.
    New tubes never ever hum. I also stock 50s & 60s vintage Sylvania chrome domes, excellent sounding tubes.
    Also, check your environment for something else that might cause hum.
    Definitely fluorescence lamps, halogen lamps, microwave ovens, old TVs (over 10 years old), old radios, poor house wiring, bad solder connections, the list goes on.

    Posts : 23
    Join date : 2012-07-11

    SP14 hum during warmup Empty Re: SP14 hum during warmup

    Post by ixe13 Fri Aug 06, 2021 10:35 am

    Here's another example of noise source that realy had me scratching my head:
    There was a very high pitch screeching buzz coming out from my speakers (nor very  loud)connected to my ST-70 amp. A new one I bought from Bob. It appeared one day out of nowhere and was intermittent. Tried everything in the book, no luck. But what got me on the right path was the fact that it was intermittent... Something on the power line maybe?  Yep, I finaly found out that it was my roomate's Mac Display monitor that had it's power supply gone bad and it was injecting noise on the power lines in our house. As soon as the display was turned on, the noise appeared. I'm aware that's this is not the type of hum you're dealing with, but my point is try to be very methodical, and dont dismiss nothing before testing it. That one really got me going.
    Good luck.

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