DRRI. No Current Reading In 6V6 Power Tube?

Discussion in 'Amp Tech Center' started by gentlyweeping, Sep 9, 2019.

  1. gentlyweeping

    gentlyweeping Tele-Meister

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    OK.
    I know this is the place where folks in the know hang out and maybe someone has an idea about this.
    My one year old DRRI is sounding ill so the first thing I checked is the power tube bias.
    I'm using one of those probes that is plugged into the socket and the tube is then plugged into the probe socket.
    Lo and behold the V8 6V6 is right at 25 milliamps right where I had set it about three months ago.

    BUT, the V7 6V6 is reading NO current at all. V7 is also only warm to the touch (it still lights up) and not hot like V8.
    I switched tubes around and even tried some different brand 6V6's in V7 with the same result.
    So the socket is the culprit and not the tube.

    I'm wondering if anyone has encountered this situation and what I might do to get this DRRI up and running.
    When it's working properly the thing sounds glorious. Thank you in advance !!!
     
  2. schmee

    schmee Poster Extraordinaire Silver Supporter

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    CHeck for any burned items on the board, resistors especially. IIRC there are a couple that fail sometimes.
    Check R65 and R66 on the power tube board replace with metal oxide or film if you need to. 1 watt.
    Check solder on tube sockets , may be a problem, especially the power tubes. If you are not good with a soldering iron, please pay a tech to do it.
    Check the screen resistors (R62, R63) to see if either is open circuit. They are 470 ohm/1 watt from the factory, also the 1.5k R60, R61
    Check the filament wires to that tube that's not heating up. Maybe the solder is bad at locations going to, or at pins 2 or 7 on the power tubes.
     
    Last edited: Sep 9, 2019
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  3. gentlyweeping

    gentlyweeping Tele-Meister

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    Wow! That was quick! Fantastic information right off the bat. I'm comfortable with replacing components so I'll be OK. You've given me a good project to get started on. I really appreciate it. Thanks!!
    (I'll check back in and let folks know how it goes :))
     
  4. schmee

    schmee Poster Extraordinaire Silver Supporter

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    I changed some of the resistor numbers in my post. Confused with other RI amps. These are just wild guesses though!
     
  5. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Voltage readings on the tube pins themselves should tell you pretty quick where the issue is.
     
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  6. gentlyweeping

    gentlyweeping Tele-Meister

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    Yep. R62 is shot. Good call. Thanks again!
     
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  7. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    Just a warning for future readers of this thread.

    "Comfortable changing components" is not the same thing as "understanding how to work on an amplifier safely."

    @gentlyweeping may understand the need and safe procedure for discharging filter capacitors before working on an amp chassis - but many.many others players do not.

    There are several very specific safety rules that need to be understood before even removing the amp chassis from the cabinet, and and followed without exception. Many tube amps can hit you with deadly voltages even if UNPLUGGED from the wall!

    Of you do not truly understand safety procedures, DO NOT work on the amp yourself.
     
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  8. gentlyweeping

    gentlyweeping Tele-Meister

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    Yes, perhaps I should have written "I'm comfortable changing components because I understand how to work on an amplifier safely".
     
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