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Magnatone Melodier Deluxe Model 109 (first amp project!)

Discussion in 'Shock Brother's DIY Amps' started by Cat MacKinnon, Aug 20, 2013.

  1. Cat MacKinnon

    Cat MacKinnon Friend of Leo's

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    after recently seeing a video on an old Magnatone Melodier Deluxe Model 109, i instantly fell in love. simple design, it'd be perfect for apartment use, and i like the fact that it featured dual 8" speakers for something a little different.

    somehow it quickly went from "i want one" to "screw it, i'm going to BUILD one!" i'm in need of a new amp and i've thought about building one for a while now, and considering how simple the circuit is, i figured this would be a good place to start. i'm working on a pretty loose timeline, in the sense that i'd like to get it finished around New Year's, which should be easily doable. this way i'll be able to spread out the cost of parts and feel like i'm getting closer to my goal, instead of just stashing away cash every week and trying my best not to spend it on something else (which i kind of have a problem with:mrgreen:) plus, this gives me the opportunity to learn more about the inner workings of tube amps, since i don't want to jump in blind. i've already spent the past few nights reading all sorts of stuff (RCA Receiving Tube manuals, tons of amp building websites, etc.) the higher-level electronics theory pretty much goes right over my head, but i'm not interested in designing my own circuits either, so for now i'm sticking with info that i think will be most important. i'm enjoying the learning process so far!

    the Melodier 109 is a pretty simple amp: one 12AX7 pre, 2x6V6 cathode-biased power tubes in P-P, 5Y3 rectifier, volume, tone. two instrument inputs and a mic input with its own volume control. here's the schematic for the Melodier 109 for those unfamiliar with it:
    [​IMG]

    fwiw, this is the ONLY schematic of the 109 online: every website has the exact same one (probably "borrowed" from the person who originally scanned it)! info about this amp is sparse, especially when it comes to the electronics. luckily i'm already to the point where i understand a lot of it, and no doubt it'll be even easier as i do more homework on tube circuits. i have found it pretty neat that i keep having these "AHA!" moments, where i learn something and then a bunch more of the circuit instantly makes more sense.

    i'm sure i'll be asking more questions as i go, but for now i've got a couple that maybe some of the amp gurus here could answer. first off i should mention what i plan on doing with the circuit, and then i'll get to the questions. i actually don't plan on making any major changes to the circuit, aside from a 3-prong power cord (natch), and getting ride of one of the instrument inputs (and perhaps the mic input. i'm still not sure if that might be a useful alternative guitar input or not.) i'll be using an undrilled chassis and i'll buy a raw cab since i already know how to cover cabinets. i'm not really interested in staying true to vintage with the components, so i'll most likely use Tefzel or Teflon wire, electrolytics instead of cans and all of the transformers i've got in mind are "stand up" type so i don't have to punch or nibble big holes in the chassis.

    ...which brings me to my first question, regarding the OT:

    Q1: all of the tube data sheets for two 6V6's in p-p suggest an 8K Ohm primary. what little info i've found regarding the Melodier 109 suggests that it most likely used an OT with a primary in the 6k6-6k8 Ohm range (as did a lot of similar amps of that era.) i'll most likely be running into an 8Ohm speaker load like the original amp, so will it make much difference as to which primary value i use? from what i gather, the 6k6 Ohm will give me a bit more lows and highs, whereas the 8K would cut those a little in favor of midrange. keep in mind that i'll most likely be using a 2x8" config (which, given their small size, makes me wonder if that's why they originally went with around 6k6 rather than 8k?)

    Q2, regarding cap voltage values: this one is probably a bit more important than the above OT question. obviously the cap farad values are on the schematic, so that's not a problem. but i'm wondering if there's an easy way to determine the VOLTAGE value to use? of course i can go higher, but that gets more expensive and space-consuming (especially with things like the filter caps.) should i go by the plate voltage, or is there a relatively simple math equation i can use?

    anyway, i think that's all i've got for now. i'm really looking forward to collecting parts, the learning process and building the thing. i'm sure i'll have other questions as i progress, but i'm also doing a ton of reading for my own benefit. after playing for 25 years, i'm glad i finally know HOW tubes do what they do, and the whole thing is continuing to fascinate me!
     
  2. Telenut62

    Telenut62 Poster Extraordinaire

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    Nice choice of amp, good luck with the build...first hurdle will be working out the layout. Study the 5F1/5E3 circuits and you won't go far wrong....that goes for the filter caps etc. usually 500v for the first two caps, 450v for the third, 160v for the coupling, 50v for the bypass. You'll pick it up as you order.

    You won't find an OT with 6.6K easily, 8ohm will be fine.

    Thoughts on what PT to use and the B+ supply? May I suggest a ClassicTone 40-18027 as it has two secondary options.
     
  3. Cat MacKinnon

    Cat MacKinnon Friend of Leo's

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    thanks! i have been cross-referencing similar amps (like the 5E3) to get an idea of values, so i'm glad i'm on the right track. i'd love to find someone that actually has one of these and has a couple photos of the internals, but i think i can handle it anyway ;). btw, you'll notice that the cathode bypass cap value is obscured on the schematic: i was going to use a 25uF/50v cap, does that sound about right? i've read that as long as i keep the value under 60uF or so i should be safe, and most similar circuits seem to use 20 or 25uF bypass caps.

    actually, ClassicTone does have at least two 6.6k OT's that would probably work perfectly (one of them has ultra-linear taps, but i'm assuming i can just not use those those if i don't need them. unless that would be an upgrade?) the TF110-48-UL is the ultra-linear one (great price too, plastic bobbin but i don't mind and it saves me nearly half the price over the same transformer with a paper bobbin.) 4 and 8 Ohm outputs.

    the other OT is the 40-18087, which is also 6.6k but has the added benefit of 4/8/16 Ohm outputs. it's a little more expensive, but i'm leaning toward that one for the flexibility with speakers. the original Melodier 109 had 2x8"* running in 8 Ohms, but additional speaker output options would be a nice bonus. there's a third OT that's basically the same price as the previous one, except it's 8k and i believe only has 4 and 8 Ohm outputs.

    as for the PT, i'm not sure yet. the power section is what i'm currently doing a bit of homework on, to get a better idea of how things work in that department. this is one of those areas where i wish i knew what the original spec was. i'm not sure what B+ voltage i should shoot for, but i'm all ears if you've got any suggestions! FWIW, i'm not going for much in the way of overdrive, and living in an apartment i'll be running clean because i'm not going to be able to crank it anyway. i'll throw a distortion or overdrive in front of it when i need to, but i don't use a ton of gain these days. since i'll also be running reverb and delay in front of the amp, that's another reason i'll be keeping it clean.

    there are a couple PT's that i've glanced at, and one of them is the one you mentioned. there's another one that's basically identical, except it's a stand-up version, which i'd prefer. if i have to punch a big hole in the chassis, i'll have to use hand nibblers...which i hate. they're hard work and take forever, although i do own a pair from years back when i modded a couple computer cases. i'd like to only have to drill holes in the chassis if at all possible, just to save myself a bit of work. if i can get all the chassis work done with just my set of step-drill bits, i'll be a happy girl indeed :mrgreen:!
     
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  5. Bill Moore

    Bill Moore Tele-Meister

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    This is the OT I decided to use for my DR build. I'm looking for clean headroom, and the option of different output impedances. Has the 6.6K primary like the original DR.
    http://www.tubesandmore.com/products/P-T1620
     
  6. G-log

    G-log Tele-Holic

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    Cool! Any idea on the value of the cap in parallel with the 2.2k resistor off the 12ax7?
     
  7. Jebrone Lames

    Jebrone Lames Banned

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    "This amp uses a configuration called "screen-fed self-split", in which you add a certain voltage drop on the screen grid of the tube being driven by the preamp, and the screen will work as a "second plate" with an inverted signal that can be taken from it. The .02 capacitor feeds this signal to the other 6V6, and the .01 capacitor helps prevent squealing. This is a cool configuration, because with a little work you can have almost 90% of signal going to the lower tube."

    Replies from this video: http://www.youtube.com/watch?v=tA7q0FWY4Q0
     
    Last edited: Aug 20, 2013
  8. laird

    laird Tele-Holic

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    Regarding the OT, I don't think the difference in primary impedance will make any difference within the narrow audio range of a guitar amp... There's a slight attitude difference between 6.6k and 8k, with the 6.6k being a little hairier and 8k being a little cleaner... Think Deluxe vs Princeton... either one should work fine, just a matter of preference.

    For cap voltage ratings, what you want to match or slightly exceed is the maximum DC voltage swing the capacitors could see. Let's say you have a PT with a 650v center-tapped secondary (325v-0-325v)... A good estimate of the peak DC voltage after rectification is to take one leg of that secondary times 1.414 (1.4 will be accurate enough), which totals 460v. You could probably get away with using a 450v rated cap, but to play it safe a 475v or 500v rated cap would be ideal.

    Considering this is a self-split push-pull design it won't be as efficient or loud as a 5e3 Deluxe or even a Princeton. PT-wise I'd expect this to use something along the lines of the Fender 125P1A used on the Champ and Princeton. somewhere around a 600v center-tapped secondary with a 5Y3... 660v would be the highest I'd go.

    G-Log - The cathode bypass cap that runs parallel to the 2.2k is commonly a 25uf/25v in many old circuits. Usually they never see more than 10v, and that's only if you swap a 12AU7 in there. All frequencies in a guitar's audio range will be bypassed with a 4.7uf or larger cap... if the amp seems boomy or bassy try reducing this cap to 2, 1, or .68uf (other popular values).

    -Laird
     
  9. andyfromdenver

    andyfromdenver Friend of Leo's

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    two 8" spkr amp would be pretty sweet! *ideas*

    good luck with el build!
     
  10. printer2

    printer2 Poster Extraordinaire

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    The amp is a self-split, which others have noted, and that implies the output is run Class A, no other choice. In that case you have to use the same plate voltages as you would any other Class A amp using 6V6's. I would say about 250-300V.
     
  11. Cat MacKinnon

    Cat MacKinnon Friend of Leo's

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    that's the video that got me interested in the amp. he's got another video where he demos 9 different amps with much better sound quality though, and the Melodier really shines in that other video.

    (skip ahead to 5:43 to hear a better example of the Melodier:)


    i've actually been chatting back and forth with the owner of that Youtube channel and he's been awesomely helpful. he says he routinely gets well over 50 messages and emails per day regarding amps though, so i don't want to take up too much of his time or take advantage of him or anything. very nice guy though and he's been great!

    that's kind of what i've gathered. in fact the guy who owns the previously-mentioned Youtube channel suggested a Princeton OT. i'll keep both in mind and just think about it, since it'll probably be a month or two before i buy the transformers.

    thanks for that info re cap voltages and transformers, it definitely helps! as for the cathode bypass cap, i plan on starting with a 25uF and seeing how that sounds. i'll get a couple other values too just to play around with, since 25v-50v caps are cheap.

    i know it's going to be quiet for its rating, which is fine. the Youtube video mentioned it's quiet for its wattage. given that i live in an apartment, that's perfectly okay with me and was in fact another thing that kinda drew me to the amp. i'm sure it's probably still too loud to dime in an apartment complex:mrgreen:.

    yeah, that's one of the things that drew me to the amp. i could go with a standard 1x12" combo, but i like the idea of having something a little different. the only downside is that using 8" speakers really limits my options, but between Jensen and Weber i can probably find something suitable and not obnoxiously overpriced. there's a local pro/live audio place that's been around for decades, and they specialize in speaker sales and repair. they're a dealer for pretty much everyone, so i'll have to take a trip down there one of these days and see what they've got. they keep a lot of demo models of their speakers for testing out in-store, which will come in handy.

    i don't know why i kept thinking it was class AB, but this is why i'm doing lots of reading and homework before i dive into the build. from a strictly player standpoint i really only care if an amp sounds good or not, not what class it is. but obviously when it comes to voltages that's kind of an important thing to know:eek:. i guess in my defense, the whole "Class A/Class AB" thing is confusing for a lot of people:mrgreen: seriously though, thanks for pointing that out, because i've been looking at the wrong section of the tube data sheets!
     
  12. syrynx

    syrynx Tele-Afflicted

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    This thread exhumed a long-buried memory from my electronic infancy: A 1950s Popular Electronics magazine hi-fi amplifier which claimed 20 watts output from a pair of 6L6s in a self-split configuration.

    It also fanned the long-banked embers of my desire to build an amp for really really cheap, the way I used to build my ham radio gear in the '50s and '60s. Series filaments... A pair of the 50B5s that nobody wants at two bucks apiece... Isolation transformer, bridge rectifier... Hmm...

    Thanks, Cat!
     
  13. G-log

    G-log Tele-Holic

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    This would be an excellent candidate for a Filmosound conversion!I was wondering if you could substitute 6V6 tubes for even lower output 6K6's in this circuit,to get the volume even lower.
     
  14. hackworth1

    hackworth1 Friend of Leo's Vendor Member

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    Printer, please check this layout for V2 and V3.

    [​IMG]
     
  15. printer2

    printer2 Poster Extraordinaire

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    Looks right to me.
     
  16. Cat MacKinnon

    Cat MacKinnon Friend of Leo's

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    now i'm confused.:confused:
     
  17. Telenut62

    Telenut62 Poster Extraordinaire

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    That's the layout for the B+ input and the 6V6 output stage.....input stage coming Hacky?
     
  18. Jebrone Lames

    Jebrone Lames Banned

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    The Magnatone Starlet 107 is lower watt alternative that would be a good beginner build. It was also sold under the Ward Airline Model 62-9022A name too. Will need a 1:1 Isolation transformer or this http://www.tubesandmore.com/products/P-T292 using the secondary 1 by itself or secondaries 1 and 2 wired in series for higher voltage. Secondary 3 could be used for heaters adding a resistor on one leg to lower voltage from 10.5 to 6.3v. Could use this OT http://www.tubesandmore.com/products/P-T31 Very inexpensive build. Will need a FWBR as shown in Doug's schematic in place of the rectifier tube shown on original.

    Schematics:

    http://www.prowessamplifiers.com/schematics/misc/magnatone_107.pdf and http://www.aronnelson.com/gallery/main.php/v/DougH/amp/Maggie/Maggie.GIF.html?g2_imageViewsIndex=1

    Videos

    http://www.youtube.com/watch?v=M3QRtAdO8J8
    http://www.youtube.com/watch?v=XyDcYVcN2HM
    http://www.youtube.com/watch?v=xwb-1vwUG0U
     
    Last edited: Aug 22, 2013
  19. Cat MacKinnon

    Cat MacKinnon Friend of Leo's

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    whew, okay. ignore that then, it was just me thinking i was losing my marbles:D. i kept comparing it to the schematic and they looked the same, but thought hackworth1 was perhaps pointing out a mistake in the schematic or something. i started thinking i was missing something important! anyway, it was just my mind wandering off into its own little world there, so pay no attention to the brain fart.

    also: thank you hackworth1, i appreciate that! i knew that drawing an amp layout for the first time was going to be kind of time consuming and lots of trial-and-error for me, so that helps a lot!

    thanks for the suggestion, but i'm sort of set on the 109. one of the things i like about the Melodier is that it uses tubes that are still commonly available.
     
  20. printer2

    printer2 Poster Extraordinaire

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    Starting from scratch I would not bother with the series string heater thing, too easy to get hum issues among other things. Is a person were inclined to use a 5L6 tube there is the 6W6GT and other variants that I can not remember the numbers for at the moment.
     
  21. hackworth1

    hackworth1 Friend of Leo's Vendor Member

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    The front end - up to the section I sketched - is a lot like a 5F2A. I would put the two cathode resistors - for the preamp tube - side by side on the far right hand side of the board. One is 2.2K and the other is 3.3K with a bypass cap.

    There is no NFB as seen on the 5F1 or the 5F2A.

    On my sketch, for clarity, I should have indicated that the horizontally drawn 470K resistor goes to ground.

    Pins 3 (plate) of each power tube goes to its respective lead off the OT.

    Pin 2 and 7 are filaments.

    Pin 1 and 6 are NC.

    That covers the atypical power tube connections.

    My feeling is that this design - with SS rectification - is well suited for a 5F1 Chassis.

    Brings another interesting and viable option to the 5F1 kit.
     
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