RadioTone DC-DC (ECL86) micro-head

Discussion in 'Shock Brother's DIY Amps' started by drneilmb, Jan 6, 2020.

  1. drneilmb

    drneilmb TDPRI Member

    Age:
    112
    Posts:
    68
    Joined:
    Nov 30, 2019
    Location:
    Decorah, Iowa, USA
    I just finished my first tube amp build, a Deluxe Micro using a DC-DC HV supply http://www.squier-talk.com/threads/cheap-tube-attempt-deluxe-micro-and-dc-dc-converter.161968/ and I was looking for something else that would be simple and give me a chance to do things better before I attempt something "real" like a JCM800 Micro. @tubelectron posted the schematic of this tiny little amp using a single ECL86 triode-pentode and I was taken with it. It's a derivative of a Magnatone 411 amp that originally had a tremolo. I thought that it would make a great match for the DC-DC converters that I wanted to use for the HV and filament supply.


    radiotone_schematic.jpg

    I'll remove the PT, the first two filter nodes and run the DC-DC converter directly to B+1 adjusted to 280V. I also went with 47uF reservoir caps on all three B+ nodes. The output transformer is an affordable Hammond 1750AX (blackface reverb transformer replacement).

    My first build used an unusual tube mounting system with the tubes mounted straight up inside the case and the tube sockets on standoffs to allow components to go underneath. For this one, I'm going to go with a slightly more traditional "chassis" where the tube and transformer are upside down and components are soldered onto the tube socket inside the chassis. I wanted to do better than just making a sketch in my notebook, so I tried using DIYLC to make a layout of what it will look like inside the chassis.

    radiotone.png

    The only board is a single piece of copper-clad board that forms a ground plane and three "islands" of copper-clad board superglued on top for the three B+ nodes. Everything else is PTP between the tube socket and the ground plane.

    I could use some help "debugging" this layout. Is there anything obviously wrong with the wire routing? I know that the construction method is very different from turret or eyelet boards and I don't have any intuition at all for what I should or shouldn't do with the longer runs of wire. I'm especially curious about the wire feeding the tone pot which looks like it will have to pass over the (DC) heater wires.

    Does anyone have any suggestions for things I should be doing differently at this stage? Components are on the way from Mouser, AES, and eBay, so I've got some noodling time before I start cutting wood, drilling holes, and making other irreversible decisions.

    Thanks in advance for any suggestions you all can offer.

    -Neil N0FN
     
    Paul-T and robrob like this.
  2. tubelectron

    tubelectron Tele-Holic

    Posts:
    728
    Joined:
    Nov 25, 2010
    Location:
    France
    @drneilmb,

    Some times ago, I asked to a member (on TDPRI, I think, but I'm not even sure :confused:) for tips about DC-DC converter - because I never used that kind of device - and my little Radio-Tone amp was in the subject : is that you ? o_O Sorry, I really don't remember... :oops:

    I'd say fine idea, indeed ! :cool::cool::cool:

    Your wiring beind extra-short and direct, you won't experience noise issue : very good point.:cool:

    You will end to a super- compact release thanks to the absence of the speaker and power transformer (but maybe the DC-DC converters would take the same room as the PT finally ? o_O).

    And of course, post pictures of your work ! :)

    I have 2 suggestions, resulting of my Radio-Tone experience - but maybe you already guessed these, right ? ;)

    1 - the ECL86 heats more than an ECC83, so provide enough ventilation in your supersmall shell design.

    2 - the gain is moderate, and IMHO you won't be able to obtain a JCM800 Marshall kind of drive, but just a crunchy/bluesy one :oops:. Here is a sound sample I recorded with a Squier std Strat on neck PU, an a touch of Cathedral Reverb EHX :



    That said, maybe the JCM800 look is the target, not the real sound... :twisted:

    -tbln
     
  3. drneilmb

    drneilmb TDPRI Member

    Age:
    112
    Posts:
    68
    Joined:
    Nov 30, 2019
    Location:
    Decorah, Iowa, USA
    Yes, that was me! https://www.tdpri.com/threads/1000-1-se-ot-under-5w.992815/ This'll be a build thread starting with the layout.

    I'll take lots of pictures, but it won't be pretty like your work. The DC-DC converters are low boards that are around 2 inches square for the largest one, so a similar format to a PT, but much less volume.

    The tube will hang down below the chassis which will slide into a shell, so it should have plenty of ventilation. conceptually like this one https://robrobinette.com/images/Guitar/Bassman_Micro/Bassman_Micro_Head_and_Cab.jpg

    Crunchy and bluesy will be great by me. This is mostly to practice amp building techniques before moving on to more complicated projects (like that JCM800 Micro).

    Thanks again for your design work on this.

    -Neil
     
    tubelectron likes this.
  4. tubelectron

    tubelectron Tele-Holic

    Posts:
    728
    Joined:
    Nov 25, 2010
    Location:
    France
    You welcome, Neil ! ;)

    OK, I see. I though that you wanted to built something even much more compact than my Radio-Tone... :rolleyes:

    Post pics : I'm curious ! :)

    -tbln
     
  5. drneilmb

    drneilmb TDPRI Member

    Age:
    112
    Posts:
    68
    Joined:
    Nov 30, 2019
    Location:
    Decorah, Iowa, USA
    I got one small delivery of caps and knobs and jacks from AES the other day and the filament DC step-down converters today, so I was inspired to start on the structural components.

    The "chassis" as I call it starts with a U of plywood. This is just scraps from around the shop. The long part is the bottom where the amp is built and the sides hold the metal front and back panels. (If I could figure out how to avoid the metalwork entirely, I would, but I've never had good luck putting jacks and pots on wood.)

    0111201511.jpg

    0111201511a.jpg

    Hate to edge screw plywood, but this isn't bearing much weight and I don't want to take up space with cleats.

    The metal panels are cut out of a serving tray that I bought for a quarter at the thrift store. Tin snips just barely handled it, plus a bit of hacksawing.

    0111202143.jpg

    Then I flatten it, trim it to size and file off the sharp edges and round the corners.

    0111202200.jpg

    This is what it should look like in place.

    0111202200c.jpg

    Tomorrow I'll hopefully finish the second panel and make the holes for the pots and jacks. Then there's a little head cabinet that this will slide into.

    The rest of the parts should arrive on Tuesday and I'll start banging it together.

    -Neil
     
  6. drneilmb

    drneilmb TDPRI Member

    Age:
    112
    Posts:
    68
    Joined:
    Nov 30, 2019
    Location:
    Decorah, Iowa, USA
    Panels finished and mounted.

    0112200933b.jpg

    0112200933a.jpg

    Then drilling holes for the jacks, pots, and power connector. First setback of many is that the coaxial power jack in my junk box doesn't fit the plug on the 24VDC power supply that I bought. Apparently there are two 5.5mm power jacks with different sized inner conductors and I have the wrong one. Oh well, Amazon to the rescue.

    0112201212.jpg

    Test fitting the voltage converters, looks good like the layout.

    Next step is the mounting for the tube socket and the little head cab.
     
  7. drneilmb

    drneilmb TDPRI Member

    Age:
    112
    Posts:
    68
    Joined:
    Nov 30, 2019
    Location:
    Decorah, Iowa, USA
    Here's what it looks like with the chassis fitted into the head cab, which with the top plate off doubles as a chassis holder. The tube and the output transformer hang down into the open space. I probably have more height in the cavity and the chassis than I need, but I don't like to be to desperately scrunched.

    0112201420.jpg

    Overall dimensions are 8"W x 6"H x 5"D. Once I get the tube socket installed I can start wiring up the power supplies to their DC-DC converters. Pots and parts come in tomorrow's mail hopefully.

    -Neil
     
  8. drneilmb

    drneilmb TDPRI Member

    Age:
    112
    Posts:
    68
    Joined:
    Nov 30, 2019
    Location:
    Decorah, Iowa, USA
    A little more progress and parts arrived today from Mouser. $3.99 shipping is great for us small timers but boy does it take a while to get here.

    I mounted the tube socket through the wooden baseplate of the "chassis".

    0115202130.jpg

    And the amazingly tiny OT goes on the far end with the leads going through two holes.

    0115202131.jpg

    0115202133.jpg

    And flipping it back to the final orientation gives a hint of what people will see in the cabinet when it's done. No grill cloth for this one, they need to know there's TOOBS in there!

    0115202134.jpg
     
  9. drneilmb

    drneilmb TDPRI Member

    Age:
    112
    Posts:
    68
    Joined:
    Nov 30, 2019
    Location:
    Decorah, Iowa, USA
    Progress inside the chassis yesterday. I hooked up the two DC-DC converters, one for the HV and one for the filaments. The main board holds the three PS caps, two dropping resistors and the pads for B1, B2, B3.

    0116201730.jpg

    Here's the first part of wiring things up.

    0117201502.jpg

    There's the DC in Jack on the top right, feeding the converters in parallel, a very short run to the heaters, and the bigger run to the HV PS board. And you can see the start of the signal wiring.

    I usually work from input to output checking things off on the schematic, but there's few enough parts here that I'm skipping the check-offs. Here's some more PTP goodness.

    0117201502a.jpg

    0117201502b.jpg

    0117201510.jpg
     
  10. drneilmb

    drneilmb TDPRI Member

    Age:
    112
    Posts:
    68
    Joined:
    Nov 30, 2019
    Location:
    Decorah, Iowa, USA
    Still troubleshooting but the wiring is all done. Here's the funniest one. What do you call an input jack with only one wire coming out of it?

    0120201707.jpg

    I thought that this would work much better... But it didn't :(

    0120201708.jpg

    Because my shorting jack shorted the input to the switched contact even when the plug was in it. Simplify, simplify, simplify.

    At this point it even behaved once like an amplifier. But the volume control was very weird. And there's a terrible noise oscillation as well.

    I made the volume control work like a volume control... Except it goes up in the wrong direction. Did I order the wrong pot? If I interchange the ends, I get no volume for most of the way and then all my volume at the end. Which I think is right. But why the wrong direction? Did I get a reverse linear pot when I needed regular? Or a regular when I needed a reverse linear?

    Oh well, more noise troubleshooting tomorrow when kids are awake and everyone is out of the house.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.


  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.