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FDP Forum / Amp Mods, Repairs, and Projects / Hot Rod Deluxe II Popping & Crackling (also no pilot light)



Jan 8th, 2017 01:43 AM   Edit   Profile   Print Topic   Search Topic

Recently my HRD began to make weird noises. It went away after a few minutes but now it's back intermittently.

You can hear it at https://soundcloud.com/user485777105/hrd-noise-dec-2016 kind of sound like popping or crackling.

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).

Any ideas what this could be?

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.

I've also done the following:
- biased the amp (around 78)
- applied contact cleaner to tube sockets & connections
- Looked at re-tensioning the power tube sockets but they're not the adjustable round half circles (omron pl08)
- safely pushed/manipulated all tubes, cables and boards while powered to see if I could find a loose connection that causes the sound.

In addition, my pilot light no longer comes on. It was intermittent for while but now, nothing.

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.

At this point I'm reluctant to order a new set of tubes if that's not the problem.



Jan 9th, 2017 02:09 AM   Edit   Profile   Print Topic   Search Topic

When it's making that noise, try plugging your guitar into the fx return.
If that doesn't stop it, remove V3 the LTP phase splitter (the amp will make a loud thump but nothing will the damaged).
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.
In the linked schematic, they're R57 82k and R58 100k.
Replacement types should be rated for at least 1/2 watt 350V operation, suggest carbon film type.
Higher rated resistors would be fine but may be a problem to fit in the pcb.

Regarding the pilot light, is the bulb filament ok, eg check for continuity?
If so, apply A LITTLE contact cleaner then refit-remove a few times.

External link

(This message was last edited by pdf64 at 04:17 AM, Jan 9th, 2017)



Jan 12th, 2017 03:17 AM   Edit   Profile   Print Topic   Search Topic

Thanks, I think I'm getting closer.

When the noise came on, I plugged into 'Power Amp In' - The noise continued.

I pulled v3 (smallest tube closest to the power tubes) - ALL sound stopped: crackle + guitar input

I'm guessing I look at replacing R57 + R58?

Also, I have continuity on the bulb so I guess I'll order a new one :)

Any further advice or feedback is greatly appreciated.



Jan 12th, 2017 05:40 AM   Edit   Profile   Print Topic   Search Topic

Yes, R57 and R58 are the chief suspects, but check that those part numbers on your amp correspond with the schematic I linked.

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.

(This message was last edited by pdf64 at 07:42 AM, Jan 12th, 2017)

FDP Forum / Amp Mods, Repairs, and Projects / Hot Rod Deluxe II Popping & Crackling (also no pilot light)

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