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HRD crackling/popping

Discussion in 'Amp Tech Center' started by Mr. Lumbergh, Aug 5, 2018.

  1. Mr. Lumbergh

    Mr. Lumbergh Poster Extraordinaire

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    I have a light-bulb limiter I built for a resto of another amp I did back in 2014 but it's in storage about 8 hours away from me, and I don't have access to a variac. I'll have to put Winston in the back room in the event of fireworks and keep my fingers crossed when I flip it on. :D

    :eek::eek::eek:
     
  2. Mr. Lumbergh

    Mr. Lumbergh Poster Extraordinaire

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    Well gents, she fired up and all the smoke stayed inside. Full volume is there on both channels, I had to keep it around 1 to avoid noise complaints from downstairs. The controls all worked such as channel switching and tone controls, drive, volume, master. I haven't tried the footswitch yet but I presume it'll work because the buttons on the chassis all did their job. The bases of the new input jacks are wider than the originals, so getting them to line up in the hole took a bit of force and the board is slightly bent back which I'm obviously hoping won't cause other issues down the road...

    It's not 100% smiles though. There was a little of the crackle that started when I took it out of standby which wasn't nearly as intense as before and quickly died down but I may need to roll tubes and see what's up.
    I also still do not have reverb. When I was in there I did clip the resistor that's part of it's treble bypass circuit so it doesn't wash out so quickly. I also swapped out the control pot with an audio 250K (I also did this on the drive pot). I know the resistance is a lot higher, but the mod destructions I was referring to said this was OK for better control and looking at the schemo it's a basic voltage divider that controls the amount of wet that gets mixed into the dry signal. I would have thought I'd get something if this was the issue by turning up all the way, but no. I kept everything I pulled off so if it's advisable I can put the original back and lesson learned but at the moment the verb is still dead. I did replace the TL072 driver for this circuit with a new one that I also socket-mounted so it's an easy swap if I aced the new one.
    I did also forget to order replacements for C20, 21, 50, 16, 14, 56, 1, 8, and 9; they're the small axial electro caps and I know that 16 is part of the verb driver circuit but is there anything else I should be looking at? I did have a bit of trouble getting the op-amp seated in the socket so I'll try putting a spare later when I get a chance but I'd like your thoughts. I want to get this going 100% before I start on my Two-Tone; it's about the same age and I want to get it recapped before it starts to fail too but I don't want to leave myself without a tube amp.
     
    Last edited: Jan 26, 2021
  3. strat a various

    strat a various Friend of Leo's

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    Sounds like you still have this issue after a couple years. Ouch.
    I have a HRD and it did this snap crackle pop thing, too. These amps have this problem related to the way they're built: it could be the tube sockets, but they are attached to the PC board, so it could be the solder joint to the PC board, which is fragile, so it could be a trace on the board.
    Also, did you try moving the ribbon cable around? Sometimes that needs to be re-routed or replaced.
     
  4. Mr. Lumbergh

    Mr. Lumbergh Poster Extraordinaire

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    I haven't made any changes to the ribbon aside from reinforcement on the boards with hot glue so they weren't flexing right at the solder points. I did go ahead and re-flow all the socket solder connections while I had it open though.
    Deoxit on the sockets perhaps?
     
  5. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Yes deoxit.
    Those sockets and ribbons can be a problem on the HRD.

    Check the reverb tank and cabling. U2 is the tl072 for the reverb. Get voltages for that.
    Try a jumper cord in the *preamp out, power amp in* jacks.
     
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  6. Mr. Lumbergh

    Mr. Lumbergh Poster Extraordinaire

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    A jumper between the jacks didn't seem to make much difference.
    The op-amp came in at -16.73V on 4 and 16.76V on 8, slightly on the high side but I don't think too bad; certainly better than the nonsense I was getting before the work. For fun I also measured the main caps in the power section: C31 - 436V, C33 - 432V, C35 - 392V, and C36 - 334V. 36 is slightly low by a couple percent but they seem to be in line.
    Is there a way to check the verb pan without having to pull it from the board completely? It's soldered and if it isn't the problem I'd sure like to avoid another teardown...
    Am I correct in thinking that the crackle only being present when cold points to sockets as a culprit?
    Not sure if it's relevant or typical but I can hear the noise increase as I turn up the verb knob despite not getting any verb.
     
  7. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Sometimes the rca jacks or cord can be the issue. Deoxit the rca connections.

    Sometimes the tank small wires can detach/break. Sometimes the springs will break. The tank kinda acts like a speaker coil driving the springs rather than a cone. It is picked up on the other side of the tank the same way. If the *spring (speaker) coil* breaks/opens, a new tank is needed. The small wires that attach to that often break which can be repaired.
    The crackle/pop that I have found is always associated with tube pin/socket problems or solder joint/PCB trace problems. Cleaning and retentioning the sockets and chop stick or visual inspection can find the issues. Carbon traces on the sockets can be harder to see/find. Cracks in the sockets are difficult to find as well. When it is crackling sometimes you can see the arcing if you look for it in a darkened room. On the HRD some of the ribbon wires are the connections to the sockets so the crackle may come from poor connections there or a broken wire inside the insulation of the ribbon wire.
    IDK???
     
  8. Mr. Lumbergh

    Mr. Lumbergh Poster Extraordinaire

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    I pulled the tank this morning and checked both sides; it looks like the transducer on the output side is done. I'm getting 57.K on the input but the out looks like it's open.
    It looks like I'm off to order a new MOD to replace...
     
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  9. Mr. Lumbergh

    Mr. Lumbergh Poster Extraordinaire

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    The new tank came in today and is installed. I replaced the 2-spring that died with a 3-spring, and it's sounding nice and lush. The removal of the treble bypass on the verb circuit also made it much easier to dial in and it doesn't turn to mush after 3. This also means I got the new op-amp installed correctly, which is of course good.
    There's still a teeny bit of crackle I noticed when I still had the back (and its shielding) off but I can't hear it now that it's back together. One thing I still do think I'll do when I get around to it too is replace those smaller electrolytic caps elsewhere in the circuit and upgrade the tube sockets to ceramic.
    She's playable now though so I can start the recap on the Two-Tone before it starts to go too. Thank you very much for your time and wisdom gentlemen, it's very appreciated.
    [​IMG]
     
    Last edited: Feb 3, 2021
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  10. Mr. Lumbergh

    Mr. Lumbergh Poster Extraordinaire

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    Well damn, it needs to get back onto the bench. It started crackling pretty badly again last night. I think I need to get those tube sockets handled.
    Does anyone know of a source for those ribbon cables or does it make more sense just to replace them? MOX also makes a great replacement tube board for the BJr. but I haven't seen anything similar for the HRD, does anybody know of one?
     
  11. TequilaCaster

    TequilaCaster Tele-Holic

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    My old rev.1 HDR started crackling. Checked the big power resistors and the plate resistors, they were OK as I had upgraded those 15 years ago. One of the power tubes was apparently failing, because when I replaced both, the crackling issue vanished. If your resistors look good, then the crackling is one or more of the power or preamp tubes.
     
  12. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    I'd confirm it's coming from the ribbon cables before playing with those.
     
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  13. Mr. Lumbergh

    Mr. Lumbergh Poster Extraordinaire

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    I picked up a set of matched Tung-Sol power tubes today and also swapped out the 12AX7's in V1 and 3 for some JJ's. I had to reset the bias also, the new tubes took it up to 67 mV from 45 but the new ones are idling at 45 now as well.
    A buddy of mine and I have been jamming on the amp now for about 4 hours, and not a single pop or crackle. I'm cautiously optimistic that I'm finally done sorting out the issues with this amp.
    I appreciate your help gents.
     
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