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    Tube amp hummmmmm

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    rfbro

    Posts : 26
    Join date : 2014-12-28
    Age : 61
    Location : Vancouver WA

    Tube amp hummmmmm

    Post by rfbro on Tue Dec 29, 2015 10:26 pm

    just came across a Knight KP-40  32 watt amp that was assembled as a kit...tubes are 4  ea 7189,,,5 ea 12ax7,,,1 7025 and 1 GZ34  all MULLARD from the 50's...I think the tubes alone were a score...The amp plays fine but for a mystery HUM my other Knight a KG 250 is dead quite.Oh yea i also have an ST-120 and a SP 9 Preamp you know ware them tubes are going..That being saidi love those little Knight amps..can anyone help me figure the mystrey of the hum...

    peterh

    Posts : 680
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Tube amp hummmmmm

    Post by peterh on Wed Dec 30, 2015 5:18 am

    rfbro wrote:just came across a Knight KP-40  32 watt amp that was assembled as a kit...tubes are 4  ea 7189,,,5 ea 12ax7,,,1 7025 and 1 GZ34  all MULLARD from the 50's...I think the tubes alone were a score...The amp plays fine but for a mystery HUM my other Knight a KG 250 is dead quite.Oh yea i also have an ST-120 and a SP 9 Preamp you know ware them tubes are going..That being saidi love those little Knight amps..can anyone help me figure the mystrey of the hum...

    120hz hum ( in US , 100 in europe) means bad electrolytic caps.
    60hz hum could be tubes ending their life and AC from filaments flods across cathode ends

      Current date/time is Fri Dec 09, 2016 7:10 pm