Pilot 210 preamp/260 amp loud buzz

Discussion in 'Tube Audio' started by ronton3, Jan 11, 2018 at 8:12 AM.

  1. ronton3

    ronton3 ronton3

    Messages:
    71
    Location:
    Macon Mo
    I have a Pilot 260 amp recapped, sounds great. I have a Pilot 210 preamp that draws power from the 260, I have never used it before because of loud hum. One of the can caps had leaked, so I just replaced the 2 can caps, and the rectifier with 4007 diodes. I hooked the pair up and they sounded really good, I was so happy, there was a very slight hum, from the 210(the 260 has been silent). I ran the the Sheffield XLO test CD, and then turned them off. Two hours later I turned them on and there is very loud, buzzing, hum that the volume control turns down. I ran the 260 with a Fisher 100-T preamp tuner and it is fine. I hope someone can tell me what is the problem. Thanks ron
     
  2. cademan

    cademan Addicted Member

    Messages:
    8,609
    Usually when hum is volume dependent, it is something relatively simple such as ground loops, bad patch cords or connections.
     
  3. gadget73

    gadget73 junk junkie Subscriber

    Messages:
    33,915
    Location:
    Southern NJ
    Do you have the hum on both channels, or just one? All inputs, phono only, specific inputs? Does it make the same noise with no source hooked up to the preamp?

    Have you checked to see if the voltages in the power supply on the SP-210 match up with the schematic? Its a slightly odd arrangement with the way it has resistors to ground.


    The way this one controls volume makes it hard to use that to determine things. It cuts signal into the preamp tubes, but also cuts output from the preamp right at the output jacks. Bit unusual, I'd hate to have to source a replacement volume pot. 4 section with loudness taps? Yikes.
     
  4. ronton3

    ronton3 ronton3

    Messages:
    71
    Location:
    Macon Mo
    Thank you for responding, there has been a big change. When I first posted I had the unit out of the case, it is sort of two parts: the main chassis and a separate input cluster at the end of about 6 or 7 wires around 10 inches long. The loud buzzy hum, that bumped the woofers, and went up and down with volume control, may have been because of bad grounding and dirty connections. I spent a lot of time experimenting, deoxitizing the controls, and checking every solder joint, cleaning inputs and tube pins. I noticed that when I pressed the input cluster down onto the chassis firmly the buzzing stopped. When I moved it a bit it would start, and sometimes if moved just right and left alone it would not buzz/hum. I notice that if I turned it from stereo to mono it calmed down, until I moved the output cluster, then it would protest again. This morning I put it back into the case: the loud, obnoxious, scary woofer pumping is gone, replaced by a steady hum on both channels, the same with or without a source, moving the controls, including volume makes no difference, except the source selection knob: I am using FM-AM for an OPPO-83 Blu-Ray-CD player, each of those different sources has a different hum level when chosen with no component hooked to them. There is phono, tape head, mic, tape rec, and mpx, I intend to use the phono ( I have recently got back into records, and am loving it), can I use the other outputs for anything beside what they say. I wish I had thought to check the voltages before I put it back into the case. I replaced the can caps with individual caps, with matching mfd, but higher voltage ratings. The hum is loud enough to be heard at 20 feet, and is independent of volume. I am wondering if I need to add another filter cap? Any help on this new situation will be appreciated, at least it is not as scary as it was. I tried the phono hook-up same thing, just a bit louder. I am going to take it out of the case again to check voltages, this time I will screw the input section to the chassis hopefully to avoid the loud nightmarish buzzyhum. Thanks ron
     
    Last edited: Jan 12, 2018 at 4:59 PM

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