Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

BUILD: Marshall 18W Single Channel w/Reverb

Discussion in 'Shock Brother's DIY Amps' started by sds1, Sep 19, 2017.

  1. Fiat_cc

    Fiat_cc Tele-Meister

    Age:
    34
    427
    Oct 8, 2016
    Melbourne, Australia
    Oh, gotcha. Looks good besides that. Getting close to firing it up!

    I've got my board populated. Haven't done s highlighter check or soldered up yet, but I check all my values with the meter as I place them, so im hoping it's correct. Once my spoils of wire arrive, ill solder the board and put it all into the chassis. Looking forward to firing this one up. The chassis layout should be much better, and I'm hoping all the changes and suggested improvements tame the trem thump. I've chop sticker version one to death and I can make the thump much worse, but can't get it any better than it is.
     
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  2. sds1

    sds1 Tele-Meister

    Age:
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    May 4, 2017
    Orlando, FL, USA
    Nice, I hope these trem upgrades do the trick. :)
     

  3. sds1

    sds1 Tele-Meister

    Age:
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    May 4, 2017
    Orlando, FL, USA
    So, slight problem. The existing chassis socket cutouts are 1" diameter. So far I can't see that anyone makes a 9-pin socket that would fit a 1" hole.

    Anything come to mind?

    The 9-pin sockets that I'm using have the non-attached mounting ring, so the socket itself will fall right thru the 1" hole. The 8-pin sockets I have, however, their mounting rings are clamped to the socket. If anyone's seen 9-pin sockets that are have an attached mounting ring that might work, assuming the mounting diameter is OK.
     

  4. Fiat_cc

    Fiat_cc Tele-Meister

    Age:
    34
    427
    Oct 8, 2016
    Melbourne, Australia
    What dockets do you have?
    I use Belton sockets. The 9 pin sockets come in a couple of flavours, but all I've used (too mount, bottom mount, and with shield bayonet) have the mounting ring crimped to the socket, and they're relatively cheap. The sockets themselves are for a 19mm hole (roughly 3/4") but the mounting screw holes are wider than that. They should work.
     

  5. sds1

    sds1 Tele-Meister

    Age:
    41
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    May 4, 2017
    Orlando, FL, USA
    Mine are a noname ceramic that I get from AES. I see the Beltons you're talking about, that helps a little but the mounting centers are 1.125" which only gives me 1/16" on either side of the cutout for a screw hole. Hmm.
     

  6. Fiat_cc

    Fiat_cc Tele-Meister

    Age:
    34
    427
    Oct 8, 2016
    Melbourne, Australia

  7. sds1

    sds1 Tele-Meister

    Age:
    41
    404
    May 4, 2017
    Orlando, FL, USA
    Cool, looks like those adapter plates would work. I have the room for them. I was just thinking about how I could fashion something similar. They do get in the way of where those RCA jacks needed to go, that needs some thought.

    Also those are $4.50 a piece. I mean maybe that's just what it takes to get out of this mess I dunno. :)
     

  8. Fiat_cc

    Fiat_cc Tele-Meister

    Age:
    34
    427
    Oct 8, 2016
    Melbourne, Australia
    I figure there are cheaper options, but that gives a design idea. Build yourself if you can. Or buy those and drill and modify as required...

    I wonder if there are bigger sockets on the market...
     

  9. sds1

    sds1 Tele-Meister

    Age:
    41
    404
    May 4, 2017
    Orlando, FL, USA
    Chassis work complete. Wasted a week mulling over those damn socket holes. Built my own socket hole adapters using some bushings and fender washers. It is solid and not too terrible looking so I'm happy. Used a silver hammered paint on the chassis this time, I like it. Hope to finish this up in the next couple of days.

    EDIT: oops my octal sockets are not aligned the same. Also you might notice my RCA goof between V1 and V2. I moved it to before V1... *shrug*

    [​IMG]

    [​IMG]
     
    Last edited: Oct 25, 2017
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  10. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    Your socket adapters look really cool. Plug that extra hole with a mod switch :D
     
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  11. sds1

    sds1 Tele-Meister

    Age:
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    May 4, 2017
    Orlando, FL, USA
    Finished the hookups and am bringing this amp up this morning. I had a dumb question though before I go further: so I was measuring filament voltage from one end to ground and then the other, and I got 22VAC and 18VAC. WTF? I'm getting around 7VAC across both leads so I'm pretty sure this is all fine and well, I just wanted to stop by before proceeding.

    What's the simple explanation for those voltage readings to ground, what is that voltage referenced to or why does it work out like that?

    Here's a pic for good measure:

    [​IMG]
     
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  12. Bill Moore

    Bill Moore Tele-Holic

    Are you using an artificial center tap?
     
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  13. sds1

    sds1 Tele-Meister

    Age:
    41
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    May 4, 2017
    Orlando, FL, USA
    No, and no center tap on the PT. Thanks for your response and sorry for not including that information in my initial post.
     

  14. sds1

    sds1 Tele-Meister

    Age:
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    May 4, 2017
    Orlando, FL, USA
    OK oops, I guess I need some ground reference on the filaments or noise is going to be an issue, yes? I can't believe I didn't run into this consideration by now, I thought my Trainwreck was w/o center tap as well, but now I remember I got a filament transformer w/ center tap.

    I don't have the resistors I need to build an artificial center tap so I will run (1.5 hour roundtrip) to the surplus store and get some because I don't feel like waiting on the mail.

    Humdinger or artificial tap? For artificial center tap The Blues Jr. schematic specifies a 47 Ohm to ground, this is a lower value than most recommend in the quick reading I did. Maybe the 500 Ohm humdinger pot is the best route.

    Either way, given the choice, do you guys feel like I should DC elevate the filament ground reference?
     

  15. sds1

    sds1 Tele-Meister

    Age:
    41
    404
    May 4, 2017
    Orlando, FL, USA
    Hey so I picked up a few resistors, and a couple of 250 Ohm trim pots as well. They are rated 1/4 watt, according to Ohm's law I believe this will suffice for 250 Ohms of resistance on a 6.3V power supply.

    Do you guys agree that 1/4 watt trim pot is OK for humdinger application?

    This is a pic of about half the capacitor/resistor aisle at that surplus store across town. They seem to have everything, but in terms of variety you're at the mercy of their current inventory. I forgot to look at their supply of wire, I was curious if they had any vintage cloth wiring at a decent price. Oh well, next time.

    [​IMG]
     
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  16. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    You're lucky to have a store like that (fairly) close by. Nice.
     
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  17. sds1

    sds1 Tele-Meister

    Age:
    41
    404
    May 4, 2017
    Orlando, FL, USA
    Came in handy today. I think it would be fun to do a build entirely with parts from that store.

    I installed a humdinger, it's wired to ground. I couldn't get my head around the idea of using the power tube cathode as a reference voltage while it's behind the standby switch? While I was looking for hints on that matter of discussion I came across that not all cathodes have an appropriate voltage for heater DC elevation. So, I just put it on the chassis ground. Anyhow, the filament voltage to ground looks normal now, so problem solved.

    I also have been updating the 18W schematic file that @Fiat_cc created to match my build precisely, so I'll share that here as well. If anyone sees anything weird, let me know.

    [​IMG]

    [​IMG]
     
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  18. printer2

    printer2 Poster Extraordinaire

    May 24, 2010
    Canada
    6.3V / 250R = 0.025A

    W = V x I = 6.3 x 0.025 = 0.16W

    We normally derate resistors by 1/2. So at 0.16W the trimmer should be rated for 0.32W. So at 1/4 watt it is a little small, especially for tube duty where the chassis will get warmed by the tubes. A one or two watt would be more appropriate. This one is about the size used back in the day.

    [​IMG]
     
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  19. sds1

    sds1 Tele-Meister

    Age:
    41
    404
    May 4, 2017
    Orlando, FL, USA
    Thanks! I went ahead and implemented a basic artificial center tap instead.

    I powered the amp all the way up this morning, everything looking great so far. This is the first time doing power up on dummy load and o-scope. I possibly see a tiny bit of tremolo wiggle with all pots at zero, this could also just be the scope refreshing or normal ripple or voltage fluctuations or whatever. On the trace below I've injected a 20mA, 1000Hz test signal at the V1A grid and probed at 8 Ohm dummy load. The output power measured is 25 watts RMS.

    I've updated the schematic to reflect the artificial center tap, as well as recording my actual idle B+ voltages.

    I shall hook a guitar up now and see what it sounds like.

    [​IMG]

    [​IMG]

    [​IMG]
     
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  20. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    I wish I had a place like this near me

    I'm glad I don't have a place like this near me!

    [​IMG]
     
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