Acetone Rockey Refresh

Discussion in 'Amp Tech Center' started by Fumbler, Apr 11, 2019.

  1. Fumbler

    Fumbler TDPRI Member

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    Hello all:

    I’ve got an old Acetone Rockey that I want to make operational. It does amplify guitar but the hum from the amp is almost as loud as the guitar output and neither the tremolo nor reverb work. I’ve read that a good approach with this amp is to start by just replacing all the caps. This will likely help with the hum at least and apparently often fixes the reverb and trem. My initial question is does this sound like a good starting point?

    Thanks
     
  2. philosofriend

    philosofriend Tele-Holic

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    At least do the power supply cap(s) for starters. They go bad from disuse and are the most likely cause of the loud hum.
     
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  3. aerhed

    aerhed Tele-Afflicted

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    Are you going to do it, or a tech? If it's you, I have to give the perpetual safety warning. But, first step is to open up and visually inventory all the gut components. Then schematic/layout comparison. Then probably caps. Like you said.
     
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  4. Fumbler

    Fumbler TDPRI Member

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    Thanks guys for the suggestions and warning. I’ll do it although I’m a total rookie with a very incomplete understanding of what’s happening in there. I will check voltages on caps and discharge anything with significant readings before I start. The amp does have a schematic with it and I have done an inventory of all the caps. The schematic lists the cap values but not voltages and only some of the caps themselves list voltage. I will post a pic of the schematic, apparently it’s very similar to an AC15...
     
  5. Fumbler

    Fumbler TDPRI Member

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    IMG_0346.JPG IMG_0332.JPG

    (with an example pic of the guts)
     
  6. Snfoilhat

    Snfoilhat Tele-Holic

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    I find it interesting how different this is from the AC15. Solid state rectified, fixed bias power tubes, reverb drive and recovery that is pretty straight-forward Hammond/Fender but not copied exactly, a tone stack very different from Vox/Marshall/Fender standard, single channel. Maybe it's just the way it is drawn, but I can't wrap my head around this power supply/rectifier diodes. I thought it was a voltage doubler at first but it doesn't look right. Maybe all the tubes are being run at very low plate voltages? And maybe (more likely) I just need another cup of coffee..

    This will be a fun project! A less well known vintage amp, almost as complicated as an AC15 or Deluxe Reverb, point-to-point wired.

    It will probably take a few iterations of replacing parts and listening and measuring the results. Large electrolytic capacitors should probably be replaced first. No, I misspoke. An incandescent light bulb current limiter should be built first. Good luck
    Ace-tone_amp_01.JPG
     
    Last edited: Apr 11, 2019
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  7. Fumbler

    Fumbler TDPRI Member

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    Thanks. I’ve read people referring to these as AC15 clones, now I know better. I will start as you suggest with the large caps and update as I go!
     
  8. Fumbler

    Fumbler TDPRI Member

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    I gave the inventory list to my local electronics shop. Not only did they not have what I needed, they weren’t able to easily track down what I am looking for. They tell me I need 600 VDC axial lead dc film type caps. Will standard electrolytic axial lead caps not work?
     
  9. Fumbler

    Fumbler TDPRI Member

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    I can find film-type online anyway, may just need to order from more than one supplier to get the assorted values.
     
  10. Snfoilhat

    Snfoilhat Tele-Holic

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    I don't want to dismiss the expertise of people working in the industry, but maybe they are mistaken. If they only saw the parts list you brought in, I don't know how they could make the jump from 100 microfarad at 200V to saying you needed 600V nonelectrolytic caps.

    But maybe you gave them some additional information or they saw the chassis or photos of it that you haven't shared here?

    The great majority of audio amps use electrolytic capacitors for any capacitance greater than (let's say) 1 microfarad. Common power supply filter caps are electrolytic, 8 - 50 microfarads at 350 - 500V (depending on the circuit). Common cathode bypass caps are electrolyitic, 1 - 220 microfarads at 25 or 50V. All the other (smaller) caps in a guitar amp will be 400V+ and made in a number of ways w/ different pros and cons but are likely functionally interchangeable.
     
  11. Wally

    Wally Telefied Ad Free Member

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    In addition to the electrolytics that Snfoilhat has indicated with the pink circles, the electrolytic bypass caps in the Reverb and trem circuit’s would be better to be replaced, also, ime. There is also a bypass electrolytic I. The power tube bias circuit...replace that as well. In short, all of the electrolytics are written with voltages as well as capacitance values. Make a list of those....I count 10. Finding those will help you to read and start understanding the schematic.
    Once you have that list, you can order from a distributor. The other caps...non-electrolytics.....are of no concern until proven to be bad, imho.
    If you want to involve yourself, Insuggest going to Duncan Tube Data to get the tube pinouts. Yes, there are pin indicators in the schematic, but a full pinout shows heaters, too. Good luck with it.
    Interesting amp. Ace Tone..... when I first saw your thread header, I thought the post was about a ‘stripping with acetone’ finish question and it was in the wrong forum. Lol.....
     
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  12. Paul in Colorado

    Paul in Colorado Telefied Ad Free Member

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    There's a guy named Uncle Doug on youtube who likes odd point to point amps, especially older ones. I suggest that you go watch his videos and educate yourself some more. There's lots to know and find his old school techniques helpful.

     
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  13. Fumbler

    Fumbler TDPRI Member

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    Thanks very much guys. A friend had also suggested Uncle Doug, I will check him out to kickstart my education! I’ll get the electrolytic caps mentioned on order and watch some Uncle Doug while I wait!
     
  14. nojazzhere

    nojazzhere Poster Extraordinaire

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    Would you post a picture of the amp exterior? I've never seen an Acetone amp. My keyboard player in high school had an Acetone combo organ.....same company? We ran it into a smallish Premier bass amp, then later an actual Leslie cabinet.....and it sounded great.
     
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  15. Fumbler

    Fumbler TDPRI Member

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    IMG_0557.JPG

    The exterior needs a refresh too but there it is. They came in black as well as white.
     
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  16. Wally

    Wally Telefied Ad Free Member

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    The only cosmetic problem I see is that that one flap of tolex on the input end of the front needs to be glued down when the chassis is next out of the cab. I like the looks.
     
  17. Fumbler

    Fumbler TDPRI Member

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    Yes, me too! The proportions are a bit different for a single 12, that’s one of the things I like about vintage amps. Nothing standardized. Regluing the tolex flap and a good cleanup (it’s more smoky-cream coloured than white right now) are the only things I will do aesthetically.
     
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