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Thread: Maddog's Lamington Jr Amplifier build diary

  1. #41
    Overlord of Music DrNomis_44's Avatar
    Join Date
    Dec 2014
    Darwin,NT Australia
    I remember building a small valve amp, called a Moonlight Amp, some years ago before I moved to Darwin, the original Valve line-up of the amp was as follows:

    V1, EF184 (Preamp).

    V2, 6SL7 (Phase Splitter).

    V3, 6SN7GT (Power Output).

    When I built the Moonlight Amp, I substituted a 12AX7 (same amount of gain but in a 9-pin valve type) because I had no 6SL7 valves in my collection of valves, I also had to make my own output transformer as well, since I had no way of buying on, to make the output transformer I pulled apart an existing one and then re-wound the primary and secondary windings according to some calculations I did with the help of a small book I bought from Jaycar Electronics, and to my surprise it worked first time, after that I made a small chassis for the amp out of some thin aluminium sheeting and then designed/etched a PCB for it, after wiring up the amp I connected it up to a power supply that I scored from the Charles Darwin Uni when I did a basic electronics course, the power supply was capable of supplying all the voltages needed to power the amp, after connecting up the amp to the power supply I switched it on and waited for the valves to warm up and then I switched on the HT supply, the amp worked first time and it was pretty loud for what it was, I could get a pretty cool valve overdrive sound from it.

    I'm definitely going to have to see if I can find the circuit for the Moonlight Amp, would be cool to try making it again after all these years, I don't have any EF184 valves but I do have an EF86 that I think I could use as a substitute, both the EF184 and EF86 are small-signal Pentodes in a 9-pin valve format, and I know that I can substitute a 12AX7 for the 6SL7, and I think I still have two spare 6SN7GT valves.

    Here's a link to a webpage where you can download a pdf of the Moonlight Amp schematic if you're interested in building one:
    Last edited by DrNomis_44; 20-07-2017 at 01:34 PM.

  2. #42
    Member Marcel's Avatar
    Join Date
    Apr 2017
    Bouldercombe Qld.
    The EF86 should work well. I've seen only one design with an EF86 in the pre-amp being a 1960's version of the AC15. You might be on to something there.

    Haven't had much to do with the 6SN7 so can't comment there other than the ax84 site has plenty of examples for guidance.

    Somewhere in my technical library I have an old 'tube substitution' book that was printed in the mid '70's.... would have some golden info if I could find it again, that's provided nobody has "borrowed" it.....
    #13 PBG SGM-1
    #12 PBG JK-2
    #11 Scratch build AC15 clone head (complete, getting EF86 mod)
    #10 PBG RCM-4F
    #09 PBG ES-1TL (complete)
    #07 partscaster Alder Denim Tele. (in progress)
    #06 PBG LP-1SSP (complete)

  3. #43
    Quote Originally Posted by Marcel View Post
    On the circuit I downloaded the resistors marked as R15 & R17 are grid stopper resistors to the push/pull output stage 6BL8's. There should not be a lot of audible difference between 4k7 or 10k however as they have recommended 10k resistors for stability then that is what you should preferably use.
    they upped it to 100k on an addendum slip of paper and the supplied parts so that's what I'm going with.

    Someone suggested setting up a switch to select between the different values but I think that would just cause problems. Apart from the fact these go between pins on the valve socket, I think they might also be structural to the wiring (provide another solder point / keep wires apart so they don't short)

  4. #44
    Quote Originally Posted by Chuck View Post
    Hey Maddogm, I'm following this thread closely as about 8 months ago I bought the same kit. Just haven't got around to building it yet!! One thing I want to do is not use the lamington tin, but make an aluminium enclosure for it. There are a couple of bits that look like they've been expoyed to the tin - do you think it would be possible to get them off and then re-epoxy them to a new enclosure? That said, I'm not even sure how you'd get them off! Here's a pic of the offending parts on my kit...

    Attachment 20958
    On mine it was just the 2 big caps. I can't remember what he said he used to stick them there but I think it's mentioned in the instructions somewhere (I don't have them with me atm). Possibly on the layout diagram.

    Once you work out what it is you might be able to work out if there's a solvent that will get it off. But it might be easier just to get replacement caps as trying to remove them may damage them. No idea on the cost of those though.

  5. #45
    Was reading this thread so joined the forum.
    Ive built this and the 15w version. The caps can easily be removed by running a sharp knife underneath. If you need to re-attach them just run a small line of silicone underneath and let dry.
    Also watch out for the orientation of the single transistor for the preamp. Its a bit ambiguous in the instructions.
    If you solder it in the wrong way the amp will work but you actually get an amazing octave up effect.
    Google the transistor pinouts and you will be fine.
    I would also like to point out that this still a high voltage amp. Safety first. You will get a jolt if you go poking around without thinking first.
    The 2w is actually a great little amp and louder than what you realise.
    Have fun!
    Last edited by Moda; 15-09-2017 at 05:47 PM.

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