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Hot Rod Deluxe Relays Dying?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Jo-Jo Beans, Dec 6, 2017.

  1. Jo-Jo Beans

    Jo-Jo Beans Member

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    Hey all, I've got a 2002 Hot Rod Deluxe (that I've posted questions about before), and I recently had some weird problems with it.

    The overdrive channel has been dead for roughly a year (really low volume, no good distortion even with everything on full) but the clean channel worked great so I just used pedals. A couple weeks ago, the clean channel also died and wouldn't get to an acceptable volume at all. Right before a gig too, of course :rolleyes: Plugging straight into the power amp worked fine and the tubes weren't to blame because I replaced them all and still had the problem.

    Earlier when the dirty channel died, I replaced one of the relays (K2 I think) based on the advice of one obscure sentence on the hotroddiy website, and the dirty channel worked again for a few hours and then died again, so I gave up and just stuck with the clean channel.

    This time, on a hunch, I replaced both of the switching relays in the amp, and whaddaya know, both the clean channel AND the dirty channel work perfectly again! I've played it for a few hours without problems but will be doing some extensive testing in the next few days.

    So after that novel-length backstory, here's the question: My amp has gone through three replacement relays now, so did I solve the problem or am I just treating the symptoms?

    Before I owned the amp, the two resistors that feed the relays - and that commonly get burned out on HRDx boards - got pulled off the board, replaced with beefy higher-wattage ones, and bolted to the metal chassis for heat dissipation. Whoever did the work did a really nice job of it too. So that common problem is dealt with, but I still wonder if somehow the relays are getting too much voltage or if something else is causing problems. Do you think I'm at risk of blowing out more relays because the rectifier or one of the other transformers is going bad or something?
     
  2. pdf64

    pdf64 Member

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    What value of resistor was used, eg 330, 470 ohms?
    I wonder if the 16V zeners they feed are ok; are you competent to safely check voltages inside a live amp chassis?
     
    Last edited: Dec 6, 2017
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  3. Jeff Gehring

    Jeff Gehring Silver Supporting Member

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    Those two resistors plus two zener diodes comprise two brute force zener voltage regulators, positive and negative 16 volts IIRC. What do your voltages read? It is possible that a zener has failed-that would allow too much voltage to get to the relays.
     
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  4. Jo-Jo Beans

    Jo-Jo Beans Member

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    They're 470 ohms, but have been beefed up to 10W versions.

    Upon closer inspection, it appears that the diodes have been replaced as well, or at least the solder on their joints has been re-flowed because there's cooked flux on the board at that spot.

    I can check voltages but I always forget the right way to do it. In this case, it would be one test lead at the cathode of those diodes, and one at ground (e.g. just the metal chassis of the amp), right?
     
  5. Jeff Gehring

    Jeff Gehring Silver Supporting Member

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    Place the black lead on the chassis metal. With the meter set for DC voltage, measure the voltage at each end of both resistors. Although if a zener had failed open , you would probably have lost op amps too...
     
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  6. xtian

    xtian Member

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    In the HRD, the reverb circuit is powered from the same 15v rails as the channel switching system. Is your reverb working?
     
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  7. Jo-Jo Beans

    Jo-Jo Beans Member

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    Hmm I didn't consider that. Yeah the reverb has always worked just fine.

    The diodes test at 16.7V and -16.8V, right where they should, and the relays are 24V relays, so voltage isn't the problem. I'm gonna keep my fingers crossed and hope that the problem has been solved by replacing the relays.
     
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  8. Jo-Jo Beans

    Jo-Jo Beans Member

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    Thanks for the help, everybody.

    I played it for another couple hours tonight with no problems, so I think it might be good to go!
     

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