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  • Relay Issue

    I've just added 2 relays to my custom amp. They are both dpdt 12v relays. One is a DS2Y http://pewa.panasonic.com/pcsd/produ...f_cat/ds2y.pdf.
    The other is a JW2SN http://pewa.panasonic.com/pcsd/produ...ech_eng_jw.pdf. These 2 relays control a few things. One of the relays (JW2SN) controls the amplified zeners which drop the B+ and screen voltages, the other relay (DS2Y) controls a paralleled bias resistor and a paralleled cathode resistor. All in all they control dropping the plate/screen voltages and the bias operation of the power tubes. Basically I'm dropping plate and screen voltages by 200v and then rebiasing the tubes to maintain the same quiescent current. I previously had this setup as a mechanical dpdt switch which only controlled the amplified zeners for the screens and B+, and was not changing the bias. While that technically worked with no problems, the tubes were in cutoff and not sounding right. So I concluded I needed 2 dpdt relays to control the 4 elements. With me?

    Here's the problem, now the amp makes a "crack" noise, like shorting a filter cap to ground kind of a sound, then hums like it's drawing lots of current. I smelled some burning and shut it off right away. From the datasheets it seems these relays are rated to work at this voltage and current. I'm wondering if my regulated relay supply is the problem. I'm attaching the schem if someone can take a look and see if they can help out with this. Yes I have the reverse biased diode across the relay supply contacts. Also of note is that the 2 new relays are in parallel w/ eachother and turned on/off simultaneously so I used 1 reverse biased diode (1n4002) for both. Not sure if that's bad practice. This is all in the "Tweed Mode" box of the power supply schem.
    Attached Files

  • #2
    As a shortcut I just disconnected the primary of the 12v relay supply transformer and the problem persists. I then removed the power tubes and still problem is there. I'm now worried I've killed my PT. Now when I switch the amp from stby into play mode it makes a nasty noise (physically, not through the speaker) in the PT general area. It's like that transformer "buzz" only louder and it sounds bad. The fuse has not blown but with a series lamp in mains the light flashes brightly and sporatically and that crackling noise is there. Shit, how could I have done this.

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    • #3
      Have you checked the relay contacts to see if there's anything left of them? I would guess from the info so far that you vaporized a relay contact which caused a short between the CT and HT2.
      -Mike

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      • #4
        You're worried that you killed your PT. So, disconnect the PT secondary wires from the rest of the amp, so that only the AC input is connected to it: do you still get the crackles and flashes?

        If so, yep, you've probably killed it.

        If not, reconnect things one at a time until you find the culprit.
        "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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        • #5
          I'll check it out. Defaced I don't see how HT2 and CT would cause any issues, they're almost the same voltage. Seems it'd be odd for those to short being that they're so similar. Will check it to make sure though.

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          • #6
            PHHHEEEEWWWW... not a relay or supply issue at all. One of the mosfets for my amplified zener B+reduction arced through it's silpad to the chassis. Replaced the silpad and shoulder washer. Used 2 stacked silpads this time. It seems fine now. Anyone dealt w/ this? Is there a better way to mount these to the chassis/heatsink?

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            • #7
              Originally posted by lowell View Post
              I'll check it out. Defaced I don't see how HT2 and CT would cause any issues, they're almost the same voltage. Seems it'd be odd for those to short being that they're so similar. Will check it to make sure though.
              I know you got the problem solved, but I'm always interested in furthering my understanding of this stuff. The CT is goes to the B+, and HT2 is the screen voltage. That's cool when idle because you're only playing with DC, but with signal applied, the CT and the screen will be 90 degrees out of phase, yes?
              -Mike

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              • #8
                hmmm, not sure bout that. Someone else'll have to chime in. I'd think that the supply voltages remain in phase, however it's possible the signal at the screens vs the plates may be out of phase. I can see how that could possibly cause issues.

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