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240hz hum through left channel

14.3.173.41

Hi,

I have a slight 240hz hum coming through left channel after about 30 seconds of warming up. Changing volume up and down does not affect volume.

I've checked and re-checked the soldering of R1-R3 etc. to no avail.

any other hints?

Follow Ups:

RE: 240hz hum through left channel - vkung 17:14:40 09/05/16 (0)
Did you do tube rolling? If yes, please check one of the left channel FETs.
RE: 240hz hum through left channel - LKP48 16:23:54 09/05/16 (21)
Sorry I should say this is TU-8200
- RE: 240hz hum through left channel - Michael Samra 16:38:57 09/05/16 (1)
  You mean 120hz I would imagine but the first thing you want to do is short the input jacks to see if the hum disappears..If it does,then the problem is in the signal path but if the hum is still there,it me be a filter cap problem. If you have one good channel,I would look for a bad ground on the input jack or take your ohm meter and measure to see if you have continuity from the input positive to the first input tube grid.
  
  "For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
  - RE: 240hz hum through left channel - LKP48 20:41:59 09/06/16 (0)
    Dear Michael,
    
    After shorting the input jacks, hum does not change.
- RE: 240hz hum through left channel - Michael Samra 16:34:36 09/05/16 (18)
  You mean 120hz I would imagine but the first thing you want to do is short the input jacks to see if the hum disappears..If it does,then the problem is in the signal path but if the hum is still there,it is a filter cap problem.
  
  "For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
  - RE: 240hz hum through left channel - LKP48 16:36:34 09/05/16 (17)
    Hi Michael,
    
    Thanks for quick response.. Nope, i definately mean 240hz.
    Will try your suggestion see how it goes.
    
    Thank - you,
    - RE: 240hz hum through left channel - Michael Samra 16:41:40 09/05/16 (16)
      I edited my post but what I want you to do is see if you have continuity between the input jack positive connection to the first tube. When you say 240hz,we usually mean 120hz in the US because we are at 120v 60cps and you guys are 100v 50cps as I recall.
      
      "For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
      - RE: 240hz hum through left channel - LKP48 20:35:27 09/06/16 (0)
        
        In Reply to: RE: 240hz hum through left channel posted by Michael Samra on September 05, 2016 at 16:41:40
        
        Dear Michael,
        
        Which point should i be checking continuity at the tube, one of the pins on the tube socket?
      - RE: 240hz hum through left channel - LKP48 17:00:46 09/05/16 (14)
        
        In Reply to: RE: 240hz hum through left channel posted by Michael Samra on September 05, 2016 at 16:41:40
        
        Thank you.
        
        I will give this a try when I get home and let you know.
        
        I'm on power from west JP so 100v 60hz.
        
        Thanks for your help
        
        RE: 240hz hum through left channel - LKP48 17:29:25 09/05/16 (12)
        
        In Reply to: RE: 240hz hum through left channel posted by LKP48 on September 05, 2016 at 17:00:46
        
        Hello
        
        I have not tried tube rolling, however I swapped the tubes on left and right side to see if it was related to the hum, however this made no difference
        
        RE: 240hz hum through left channel - vkung 17:35:39 09/05/16 (11)
        
        In Reply to: RE: 240hz hum through left channel posted by LKP48 on September 05, 2016 at 17:29:25
        
        I will check Q3 & Q5. If both Q3 & Q5 are ok... you need to check each soldering point on the left channel.
        
        RE: 240hz hum through left channel - LKP48 19:01:38 09/05/16 (9)
        
        In Reply to: RE: 240hz hum through left channel posted by vkung on September 05, 2016 at 17:35:39
        
        Dear Sir,
        
        While checking your suggestions Q3 & Q5... I was double checking everything around this area and noticed that Zenner Diode ZD1 is allowing current to flow through both directions.
        
        Seems like this may be an issue! > . <
        
        I will replace today and report if issue is corrected.
        
        Thank-you for all your help.
        
        RE: 240hz hum through left channel - vkung 19:11:57 09/05/16 (8)
        
        In Reply to: RE: 240hz hum through left channel posted by LKP48 on September 05, 2016 at 19:01:38
        
        yes.. Once you replace the FET... it will solve your problem.
        You need to replace or check your left channel's output tube.
        
        RE: 240hz hum through left channel - LKP48 19:16:00 09/05/16 (6)
        
        In Reply to: RE: 240hz hum through left channel posted by vkung on September 05, 2016 at 19:11:57
        
        Thank-you
        
        I will replace Q3 and Q5 with 02N60Z
        
        Is there a specification for Zenner Diode, in assembly instruictions it is only refered to as Zenner Diode with no more detailed information.
        
        RE: 240hz hum through left channel - vkung 19:21:42 09/05/16 (5)
        
        In Reply to: RE: 240hz hum through left channel posted by LKP48 on September 05, 2016 at 19:16:00
        
        YOU DON'T NEED TO REPLACE THE DIODE.
        
        RE: 240hz hum through left channel - LKP48 20:34:02 09/06/16 (4)
        
        In Reply to: RE: 240hz hum through left channel posted by vkung on September 05, 2016 at 19:21:42
        
        I have replaced Q3 (did not replace diode)
        Still getting hum occuring on left channel.
        
        Also re-soldered every connection. Should i Also replace Q5?
        
        RE: 240hz hum through left channel - vkung 23:29:41 09/06/16 (3)
        
        In Reply to: RE: 240hz hum through left channel posted by LKP48 on September 06, 2016 at 20:34:02
        
        CHECK THE VOLTAGE AS PERV Page 19
        
        RE: 240hz hum through left channel - LKP48 07:33:37 09/07/16 (2)
        
        In Reply to: RE: 240hz hum through left channel posted by vkung on September 06, 2016 at 23:29:41
        
        All points voltage checks ok
        
        Any other tips?
        
        RE: 240hz hum through left channel - vkung 09:48:54 09/07/16 (1)
        
        In Reply to: RE: 240hz hum through left channel posted by LKP48 on September 07, 2016 at 07:33:37
        
        where you bought your kit?
        99% is the soldering issue..
        
        RE: 240hz hum through left channel - LKP48 03:07:02 09/08/16 (0)
        
        In Reply to: RE: 240hz hum through left channel posted by vkung on September 07, 2016 at 09:48:54
        
        Dear Sirs,
        
        I removed all components related to power filter, added new FET for Q3 / Q5, and resoldered everything. HUM is solved.
        
        Thank-you for your help.
        
        RE: 240hz hum through left channel - LKP48 19:14:57 09/05/16 (0)
        
        In Reply to: RE: 240hz hum through left channel posted by vkung on September 05, 2016 at 19:11:57
        
        Ｉ　ｗｉｌｌ　ｒｅｐｌａｃｅ　Ｑ3　Ａｎｄ　Ｑ５
        Ｗｉｔｈ　０２Ｎ６０Ｚ
        
        Ｉｓ　ｔｈｅｒｅ　ａ　ｓｐｅｃｉａｌ　ｚｅｎｎｅｒ　ｉ　ｍｕｓｔ　ｒｅｐｌａｃｅ　ｗｉｔｈ．　ＴＵ－８２００　ｉｎｓｔｒｕｃｔｉｏｎｓ　ｓｉｍｐｌｙ　ｃａｌｌ　ｉｔ　Ｚｅｎｎｅｒ　Ｄｉｏｄｅ　ｗｉｔｈ　ｎｏ　ｆｕｒｔｈｅｒ　ｓｐｅｃｉｆｉｃａｔｉｏｎ．
        
        RE: 240hz hum through left channel - LKP48 17:46:20 09/05/16 (0)
        
        In Reply to: RE: 240hz hum through left channel posted by vkung on September 05, 2016 at 17:35:39
        
        Thank you I will check
        
        RE: 240hz hum through left channel - Michael Samra 17:19:04 09/05/16 (0)
        
        In Reply to: RE: 240hz hum through left channel posted by LKP48 on September 05, 2016 at 17:00:46
        
        Then your hum would be 120hz from the power supply just like the US
        
        "For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

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