Cloning a Silvertone 1482

Discussion in 'Shock Brother's DIY Amps' started by ArcticWhite, Aug 19, 2018.

  1. ArcticWhite

    ArcticWhite Tele-Holic

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    Tremolo pot taper for this amp?

    Fender typically uses a 3meg reverse audio pot, with a 100k voltage divider..

    The Silvertone schematic shows a 1meg pot with a 68k resistor, and doesn't specify taper. The official service parts list shows both ttrem pots as the same part number as the volume pots.
     
  2. ArcticWhite

    ArcticWhite Tele-Holic

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    Anyone?
     
  3. Mr Ridesglide

    Mr Ridesglide Tele-Afflicted Silver Supporter

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  4. ArcticWhite

    ArcticWhite Tele-Holic

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    SHE'S ALIVE.

    Fired right up - after I fixed a couple errors I made in the heater wiring. Unlike most amps, this Hammond chassis has the 12AX7 sockets rotated to different angles, and that threw me.

    First observation: building this circuit, without a layout or a similar amp to copy, was WAY more difficult than I thought it would be. And now that I've built it, I understand why the Silvertone has it's controls layed out diagonally - because without a tag board, you need to get your pots really close together, and close to the preamp tubes, and jacks, etc.

    It's was a real bear developing a layout on the fly. I ended up using a couple of terminal strips that I pulled from my Hammond amp graveyard, and working slowly and methodically.

    Voltages are mostly about 10 percent lower than design value. Should I reduce the value of the first big resistor (2.2k)?

    The amp isn't complete yet, as I have not built the tremolo circuit. I wanted to check it out and troubleshoot if necessary, before it became more complicated.

    But it works fine, so I'm ready to finish up.

    Question:
    I'm no expert on grounding. My pot cases are currently not grounded. Should they be? If so how and where?

    The amp is dead quiet right now. With volume on 10/12, and the guitar on 9, there's just a faint hiss. It's the quietest amp I own so far. Hope the tremolo doesn't upset the apple cart.

    20190613_220049.jpg

    I used a pair of 47k resistors because I didn't have a 2 watt piece in the correct value of 27k. The cap can is a 50/50 from Antique Electronic Supply. It cost about 8 bucks. Third electrolytic is 22mf. (Edit: 22uF)

    20190613_220034.jpg

    I built the power supply and power tubes first, so I could check voltages. They were around 400 volts, so I continued building.

    20190621_111300.jpg

    I think I have just three ground points so far.

    20190621_111348.jpg

    Controls are: Vol Tone jacks - Vol Tone jacks - Speed- light - Intensity.

    Channel two is not connected because I need another switching jack. How should I go about grounding the pots?

    20190621_133607.jpg

    20190621_133601.jpg
     

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    Last edited: Jun 22, 2019
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  5. Asmith

    Asmith Friend of Leo's

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    I assume that 3rd electrolic cap is 22 microFarad (uF) not 22 milliFarad (mF). The pots are grounded through thier mechanical connection to the chassis so they don't need thier shells soldering anywhere.

    Keep your ground points close to the earth connection that goes to your wall so that the current doesnt travel across your chassis creating potential noise unless the grounded sections arent high current. I've built an amp on a few tag strips before and ran all the ground paths straight to a point next to the IEC socket, that terminal also connected to the IEC earth. This was with the exception on some shielded cable shields which went to any possible ground connection as long as it was close. If you haven't got any noise issues then I wouldn't change anything though. If you ever do point to point again its worth getting DIYLC, it's a free layout software for aimed at guitar stuff, you can plan your layout before you start and should remove some of the difficulty involved and help reduce some mistakes. My next amp build will be a micro amp based on Vox AC15 for my sister and I used the software to design the layout and has allowed me to get a compact layout planned so it can fit into a very small enclosure while keeping the transformers/valved in ideal locations.

    Regarding your voltages have you checked your wall voltage? It may be 10% lower than what your PT is designed for.
     
  6. Nickfl

    Nickfl Tele-Afflicted

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    What did your voltages end up being, how close did we get on those voltage estimates in the other thread?
     
  7. ArcticWhite

    ArcticWhite Tele-Holic

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    Voltages are about 8 to 10 percent lower than the Silvertone Schematic. B+ is about 320V. The Silvertone wants 350V.

    320V is in line with the Hammond schematic.

    I have not connected the AU6 of the tremolo circuit yet. Will update later.
     
  8. Nickfl

    Nickfl Tele-Afflicted

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    Are all your voltages about 10% low across the board? If so I would consider just switching to a different rectifier tube, a gz34 would probably add enough to get you pretty close to the schematic voltages.

    I'm surprised the B+ is exactly the same as the hammond with the lower current of the 1482, have you checked your bias?
     
  9. ArcticWhite

    ArcticWhite Tele-Holic

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    Haven't checked bias yet.
    I'm in the middle of building the tremolo circuit now, so it's a bit of a mess. I'll measure bias when I can.
     
  10. ArcticWhite

    ArcticWhite Tele-Holic

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    Built the tremolo circuit, and corrected a couple of mistakes I made, and the voltages are now right where Nick predicted. About 10% higher than the Silvertone Schematic.

    The tremolo was very difficult to build, mostly because I didn't use the layout design software you guys recommended - because I wanted to see if I could do it. And because I got this far without one.

    The wiring looks like a rat's nest, but I think it turned out pretty cleanly, for a P2P amp, built in an organ amp chassis that wasn't designed for it. It's very quiet - no mains hum and very little hiss.

    It sounds pretty great too! I don't have a real 1482 to compare it to but I suspect it is louder, and has a tighter bottom end, due to the robust transformers, and the 50/50/20 filter caps.

    I built channel two stock but with Fender style hi-lo inputs, and grounding jacks. Channel one got a 33k grid stopper, and a 4.7uF cathode bypass capacitor, so it gets very crunchy very early. Nice touch sensitivity too.

    The tremolo is very pleasing, but definitely too fast for my taste, so I have substituted a .047 uF or larger capacitor for the. 02 that connects to the screen grid of he 6AU6.

    It worked nicely, but I don't really know which cap is the best to swap, or if I should increase each of tremolo cap values. Will different cap values make the tremolo asymmetrical?
    I'm looking to experiment, and I think I might like a wobbly sort of sound. Ideas?

    Next up: building the cabinet for the head and 2x10 speakers. I'll be using a pair of vintage Jensen P10Rs I pulled from a Hammond chord organ.

    This thing is way messier than the original.
    20190625_214408.jpg
    Looks like an amp.
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    The tremolo
    20190625_214419.jpg

    Measured Voltages are penciled in. I modded the schematic to show the 5U4 rectifier of the Hammond donor amp.
    20190625_233804.jpg
     
    Last edited: Jun 26, 2019
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  11. symbiotic

    symbiotic TDPRI Member

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    Well done! And good luck with the trem, although I don't have any advice to offer. One thing - are you sure you can't be talked into a combo cabinet with the amp vertical along the side? :)
     
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  12. shortcircuit

    shortcircuit Tele-Meister

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    Very nice. I've been curious about that tremolo circuit with the grid leak biased pentode. Clever bit of engineering.
     
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  13. ArcticWhite

    ArcticWhite Tele-Holic

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    I considered that for sure. But the problem with the original design is that it places most of the controls so near the floor. Kind of a pain to use. The amps look like TVs, but unless we put them on a TV table, they're sort of silly, from a functional standpoint.
    I'm definitely going for a mid-century look however. Amps cabinets mostly look as though they came from the same factory these days. Most of them look like shrink wrapped cardboard boxes.
     
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  14. ArcticWhite

    ArcticWhite Tele-Holic

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    It sounds pretty great once you have the range right. Sounds almost like a Leslie.
    I know there's probably not any pitch shifting going on, but dang, it sounds like it. It's smooth.
     
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  15. ArcticWhite

    ArcticWhite Tele-Holic

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    So I've noticed the amp motorboats occasionally, but only on the channel with the cathode bypass capacitor.
    If I turn that channel's volume down it stops.
    I didn't use shielded cable for my input leads, because they weren't in the original design. But my runs are longer, and more cramped.
    What's the most likely cause?
    My caps are all brand new, and most of the resistors are too. I did use old resistors in the power supply, but I tested them first.
     
    Last edited: Jul 4, 2019
  16. shortcircuit

    shortcircuit Tele-Meister

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    I'd try putting the 68K grid stopper resistors directly onto the socket. You can use the empty socket next to it to mount them.
     
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  17. Nickfl

    Nickfl Tele-Afflicted

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    Check to make sure none of the tubes are microphonic, that can cause the amp to start oscillating if everything is arranged just so.

    You might also try a small snubber cap across the plate resistor on the cathode bypassed input.
     
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  18. ArcticWhite

    ArcticWhite Tele-Holic

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    Started the cabinet this weekend.
    Decided on a 2x10 combo rather than a head and cabinet.
    I'll be loading it with a pair of 50's Jensen P10r drivers I pulled from a Hammond chord organ.

    I do lots of drawing before I cut. I started with a head and cab, before settling on the combo.

    20190708_081610.jpg

    20190708_082340.jpg

    I liked the idea of slanted cabinet face, but it didn't work with the mid-century department store vibe I was going for. So I hit on the idea of a slanted baffle hidden behind a vertical grille cloth.

    20190708_081723.jpg

    Box joints are relatively simple once you have built a sled jig.
    But somehow, one of my box jointed ends got spaced unevenly and I had to cut a new panel.

    20190707_172755.jpg
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    I like the way the grille cloth wraps around the corner of some old Gretsch and Magnatone amps.

    20190707_212601.jpg

    20190708_081715.jpg
     
    Last edited: Jul 8, 2019
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  19. ArcticWhite

    ArcticWhite Tele-Holic

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    Cabinet is taking shape now.

    20190709_022212.jpg

    Showing how the grille cloth will wrap the corner.

    20190709_022028.jpg

    20190709_022731.jpg

    Even with all the drawings and measurements I made, I still wound up building the cab about an inch too short. There wasn't quite enough room for the top of the grille frame to clear the PT, so I had to shim the chassis back from the face of cabinet with a piece of 3/8" birch ply, and notched the grille frame a bit.

    20190709_022133.jpg

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    I don't know if the tilted back baffle is going to work either, as the transformer will interfere with it too.


    Using the Hammond chassis in a combo is pretty awkward. The speaker jacks and tremolo jack are pretty deep inside. I may relocate the tremolo jack to the face or the even the top of the amp.

    Cab is 23 wide x 21 tall and 10 deep. Might trim it to 9 or 9.5 deep.

    Would have been much simpler to do a head and cab.

    It just occurred to me that I trimmed the chassis down from 21 inches, unnecessarily as it turns out.
     
    Last edited: Jul 9, 2019
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  20. ArcticWhite

    ArcticWhite Tele-Holic

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    Moving right along. I figured a way to make the tilted baffle design work leaned back at about 8 degrees.

    Screwed it to the grille assembly, and loaded it up for a test run.

    Sounds great. The pair of 10" speakers makes for a fuller sound than a single 12".

    I test drove it for a while, compared it back and forth with the 2x12 cab I built this spring. The 2x12 has a pair Jensen C12r (ceramic) while the Silvertone is currently loaded with Alnico P10r. So it is an interesting contrast.
    The ceramics are a little bit brighter, with more sparkle, and they break up with more of a grind. The AlNiCos are darker and the breakup seems more organic and darker.
    Alnico is more compressed, as the ceramics exhibit more dynamic range.

    Two flavors. Both are tasty.

    20190709_213841.jpg 20190710_090525.jpg
     
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