FDP Forum / Hot Rod Deluxe II Popping & Crackling (also no pilot light)/ 4 messages in thread.

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fandangoflip



Australia

Jan 8th, 2017 01:43 AM        

Recently my HRD began to make weird noises. It went away after a few minutes but now it's back intermittently.<br /> <br /> You can hear it at https://soundcloud.com/user485777105/hrd-noise-dec-2016 kind of sound like popping or crackling.<br /> <br /> The recording is the amp with no inputs, foot-switch or fx loop - Just the amp. It happens on both clean and gain channels. From about 12 seconds onwards, I press all the buttons and turn all the pots in order (left to right).<br /> <br /> Any ideas what this could be?<br /> <br /> Earlier in the year I had some humming issues so replaced the caps and the large white resistors (R28+29?). The pre-amp valves were also changed not long before that but one went microphonic so I'm back to the stock ones.<br /> <br /> I've also done the following:<br /> - biased the amp (around 78)<br /> - applied contact cleaner to tube sockets & connections<br /> - Looked at re-tensioning the power tube sockets but they're not the adjustable round half circles (omron pl08)<br /> - safely pushed/manipulated all tubes, cables and boards while powered to see if I could find a loose connection that causes the sound.<br /> <br /> In addition, my pilot light no longer comes on. It was intermittent for while but now, nothing.<br /> <br /> Advice would be hugely appreciated. I'm postponing taking it to an amp tech just yet as I really want to learn about my gear.<br /> <br /> At this point I'm reluctant to order a new set of tubes if that's not the problem.<br />



pdf64



UK

Jan 9th, 2017 02:09 AM        

When it's making that noise, try plugging your guitar into the fx return.<br /> If that doesn't stop it, remove V3 the LTP phase splitter (the amp will make a loud thump but nothing will the damaged).<br /> If the only thing that stops the noise is operating without V3, then it indicates that the LTP plate resistors (a known weak point) may be bad.<br /> In the linked schematic, they're R57 82k and R58 100k.<br /> Replacement types should be rated for at least 1/2 watt 350V operation, suggest carbon film type.<br /> Higher rated resistors would be fine but may be a problem to fit in the pcb.<br /> <br /> Regarding the pilot light, is the bulb filament ok, eg check for continuity?<br /> If so, apply A LITTLE contact cleaner then refit-remove a few times.<br />



fandangoflip



Australia

Jan 12th, 2017 03:17 AM        

Thanks, I think I'm getting closer.<br /> <br /> When the noise came on, I plugged into 'Power Amp In' - The noise continued.<br /> <br /> I pulled v3 (smallest tube closest to the power tubes) - ALL sound stopped: crackle + guitar input<br /> <br /> I'm guessing I look at replacing R57 + R58?<br /> <br /> Also, I have continuity on the bulb so I guess I'll order a new one :)<br /> <br /> Any further advice or feedback is greatly appreciated.



pdf64



UK

Jan 12th, 2017 05:40 AM        

Yes, R57 and R58 are the chief suspects, but check that those part numbers on your amp correspond with the schematic I linked.<br /> <br /> If the pilot lamp has continuity then try a little contact cleaner (even something like WD40 would be fine here) and remove/refit the bulb a few times, to help clear off any surface contamination.



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