Building session at the 2007 Fest?

Discussion in 'AK Fest 2006' started by PakProtector, Apr 26, 2006.

  1. PakProtector

    PakProtector AK member

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    Hey-Hey!!!,
    Any intrest in building something at the 2007 Fest? Something useful, yet simple enough to actually get done before we have to depart on Sunday? I have a few ideas...

    Some suggestions...sign up, and pay for the materials. Probably a bit for some tools too. Build on Saturday, listen on Sunday...:)

    The timeframe will limit the scope of the project, but it shouldn't have to restrict it too far.
    cheers,
    Douglas
     

     

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  2. rca2000

    rca2000 Super Member

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    Let me see if I can figure out what you mean::

    Are you speaking of a room or such, where a group of people get together, pay for a "parts kit" or such of materials(for say, a SE 6bq5 amplifier), and each of them put one together, under the supervision of a tech??

    I could see how something like that would be popular. I don't know how cheapley it could be done, but it WOULD be educational, for those involved.
     
  3. PakProtector

    PakProtector AK member

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    Yep, that's about the size of it. I had not thought to plan the project, but a SE amp like you described could certainly be done quite easily.

    Actually, having heard the neat little amps at the Fest, a SE E-Linear 6BQ5/EL84/6Pi14 amp would be an excellent project. The most important piece will be the output Iron. The rest can be done in a small custom run from a local winder.

    'pends on what students are willing to pay for such a project.
    cheers,
    Douglas
     
  4. Kamakiri

    Kamakiri The New Dynamic

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    I think it would be an excellent idea.

    The only thing at issue is the time factor. Seems like it's hard enough to squeeze in enough time to see all the rooms let alone to get in a project that would take up an afternoon......
     
  5. PakProtector

    PakProtector AK member

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    Hey-Hey!!!,
    The time constraints are not a small issue for sure. The design would be one offering good performance right off, with room to grow.

    Power supply design with maximum flexibility is just a matter of cost. The SE circuit RCA2k mentioned is a good starting point. Have to see about interest, as it's the final reason to put it on.

    Spreading the DIY craft is a neat project. The Fest is an excelent venue. I thoroughly enjoyed myself looking at the stuff others had built and exploring in rooms I'd heard good things about. I think I got to them all....:)

    One of the really cool things about DIY is discovering that there is nothing complicated about amp construction. No magic involved. It was a bit of a revelation for me to discover that the box with tubes sticking out of it was just a bunch of parts.

    Now to the fun part, design a circuit that can be assembled quickly, and with minimum experience. Low parts count, and an intuitive circuit will be the order of the day.

    Easy to drive pentodes, like the EL84 or 7591 look good at this point.
    cheers,
    Douglas Piccard
     
  6. WhiteSE

    WhiteSE Is Lute Gluten Free?? Subscriber

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    I am all over that idea...Nothing like hands on experience to learn!!
     
  7. PakProtector

    PakProtector AK member

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    So then, we have a little bit less than a year to prepare. There is much to be done.

    I looked at 7591A data...at 300V B+, and a 6k a-a plate load, a pair of pentodes in Class A will make 22W. 6k6 a-a, and U-L rigging should drop that a few watts. Drive it with a LTP pair of pentodes like 12BY7 or EF184 and we're off. With a custom Heyboer power TX, there'd be the option of a negative rail for those scared of SS current regulators.

    Class A takes the PS out of the equation for the most part. 400V 'lytics would be a viable option. A small inductor (~4 Hy/150 mA ) will do wonders for PS filtering. there is a limit to how far I'm willing to simplify and cut stuff out...these will be excellent amps.

    The output TX leaves a whole lot of options. A very nice custom from Heyboer will be less than $80 ea. in quantity. NC-wound copies of the Peerless S-230-Q perhaps?

    So, somebody who wants to try some of the prototyping will need to step up. I'm not going to be picky on this one, but I'd rather a local member. No issue if it's more than one member...

    For the Fest build. Chassis plate from Front Pannel Express. Assorted hardware to attach all the Iron. Parts acquired in build-lot quantity to be distributed while underway. Tubes from any number of sources. There has got to be several sources of 7591A in JJ or EH.

    To pay for it all, likely a 2.5 month lead time, up-front payment...it would make the perfect Christmas present...:)
    cheers,
    Douglas
     
  8. tubino

    tubino A guy with too many tubes Subscriber

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    If you wanted to go with a really inexpensive yet proven SE triode design (but low power), there's Bob Danielak's "Darling" amplifier, using 1626 tube driven by 8532. I could donate some tubes, some PS iron, ... maybe even some prepunched chassis plates. I managed to scavenge some, years ago that already have holes for a 7 pin mini, a 9 pin mini and an octal socket. I built a Darling using one plate (they are small!) per channel. You need a 12 volt supply for the 1626, but it's a tiny xformer.

    Nice thing is that with such low current and watt numbers, the OPTs can be whatever you scavenge from an old Grundig, RTR, little Japanese stereo amp, whatever. You might get by just fine with PP iron too. I've heard old Fisher and Scott iron with 20ma unbalanced DC running through it, and it can work just fine. There's probably a little gap in there to help prevent saturation...

    Google Bob Danielak Darling amp and you'll get the schematic. Two tubes per channel, very low parts count, great first project.
     
  9. Kegger

    Kegger R.I.P. 1/12/1966 - 6/1/2017 Super Mod Subscriber

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    All very cool stuff and I'd be up for it.

    But if I had to make a choice betwen el84's and 7591's, I'd say el84's, there cheaper
    and are much more available both as nos and new stock.
     

     

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  10. PakProtector

    PakProtector AK member

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    Good points Kegger. The PS is also smaller, lighter and less expensive.

    There are a few things required in order to keep my enterest:
    PP topology.
    Class A finals
    Cnservatively-run PS iron.

    I prefer pentodes over triodes for voltage amplification.
    I see no need to develop any design that requires tweaky, 'spensive parts.
    I'd rather not make too much of a compromise on the output Iron. <$100 each.
    cheers,
    Douglas
     
  11. WhiteSE

    WhiteSE Is Lute Gluten Free?? Subscriber

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    i am all about big butted trannies...the rest can be small...:)
     
  12. tubino

    tubino A guy with too many tubes Subscriber

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    Doug, it's your idea, so you can call the shots! (and I'm with you for 2 out 3 in your list above!) I just wanted to throw out an alternative, esp. one with the KISS (Keep it Simple, Smartie!) principle. If I can just offer one other suggestion: use good tubes, but cheap tubes! With so many really great tubes cheaply available just because they are not fashionable, why not design around them? With some you can buy a lifetime supply for less than the price of a 7591.

    My two cents.
     
  13. mhardy6647

    mhardy6647 AK Subscriber Subscriber

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    Using a PCB can speed the project immensely. Setup costs for a run of PCB's is pretty low... and, believe it or not, PCB wired hi-fi can sound very good, too!

    Consider a headpone amp or line-amp as a project. The former can get a lot of bang for the buck (cf. Pete Millet's low-voltage hybrid headpone amp, of which I am quite enamored -- http://www.pmillett.com/hybrid_head.htm )
     
  14. PakProtector

    PakProtector AK member

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    Hey-Hey!!!,
    There are all sorts of neat valves to try. 13EM7 for one. Two for a PP amp. really decent performance available too. I heard some this weekend at the Oswald's Mill event. It was SE...but there's plenty of instruction available for SE design.
    cheers,
    Douglas
     
  15. tubino

    tubino A guy with too many tubes Subscriber

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    I think Bottlehead's first SEX amp used 6EA7 / 6EM7... Or was it 6DN7? Anyway it was a dual dissimilar triode with one half good as a driver, the second half as a power amp, not far from the 6DN7. Doug, if you wind up offering a building class with some tubes like these, I think I can supply all the tubes needed. They aren't expensive to order, but I'm offering for free, and I can deliver for free too!

    I know you prefer PP, but if you can compromise your principles just a bit :D , you can REALLY keep down the number of components AND the number of solder connections. I know to an experienced builder like you, adding a phase inverter stage with plate resistor, cathode resistor, etc. is no big deal, but first-time builders may need a lot of time just wiring and soldering PS and two stages. Even if you start with all metalwork done, you would need ALL of four hours to get a class of 4-8 folks to mount sockets and transformers and input and output jacks, switch, term strips, fuse, and then wire everything up -- and that's even if you keep it as simple as two diodes and LRL for PS, driver and output stage. To make sure everyone leaves with a completed, tested amp, I think a full day would be needed. But the cool thing about hardwiring a simple amp is that folks have a real chance not only to get it done and checked out, but they can get a real in-the-fingers knowledge of what a plate resistor does, how GROUND works in both the AC and DC circuits, how the OPT is a path for both the B+ and the audio signal etc. I would argue that the learning advantage of hardwiring (over using a PCB) is substantial for DIY amp building, and the simpler the circuit, the smaller the time advantage of a PCB. And the circuit can be explained pretty easily to beginners.

    But I'm openly biased in favor of SE, so take that into account.
     
  16. PakProtector

    PakProtector AK member

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    3,654
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    Hey-Hey!!!,
    The trade-off between PP and SE is in the power stage. SE has to be quieter, specially if triodes are used. This would be a two stage amp, regardless of PP or SE.

    There are some other neat TV combo valves that are quite inexpensive...some research is needed.

    Like I laid out in the beginning, there are a few things to get settled. Interest level for one. Project topology for another. Then I'd need some local Beta folks who'd take on the first batch of builds. Ideally this group would be able to consult and assist in the actual class next year.

    I'd rather do PP, but a medium-sized SE amp can be done really well in a simple fashion as well. See Pete Millett's aX write up on the E-Linear amp from about a year ago. The PDF is on his site. That one done with EL84 would be pretty sweet. Probably just as well with a 7591 or 6V6.

    The bottom line is that this class would be one heck of a lot of rewarding work. In truth, it's more than I should probably bite off by myself. What I'd like are some of the rezident Masters to step up and assist in what ever capacity they'd be comfortable with.

    This would be a neat meeting theme for the SE Michigan AK group to tackle together IMO.
    cheers,
    Douglas
     
  17. tubino

    tubino A guy with too many tubes Subscriber

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    VERY NICE! Here's what I like about it, in no order:

    Decent power for simple SE amp
    No global NFB, but uses UL tap as B+ for driver stage. How cool is that?
    Power supply: high-current damper diodes! YES!
    CLCLC with Smart filter cap setup: 10-40-40, and smart filter chokes: 10h 35R, 1.5H 50R (low DCR) I bet that models well in PSUD for a low-impedance supply
    OD3! Bring on the glow!

    I think the schematic looks very hip. Plus he's got parts lists, layout tips...LINK to schematic etc.

    And he's giving it all for personal use, so in my opinion you couldn't do much better than this for a group project. (lots of OTHER ways to do it, but BETTER all around?) Sure, I like triodes, but this amp would get all kinds of speakers going while keeping it pretty simple. Anything cheaper/simpler will have some real compromises in power or elsewhere. The power supply in Millett's design is more beefy than you need, but not more than you want! As Doug noted, PS is gosh-darn important in SE, and the filtering here is done RIGHT to give a lot of easy low-impedance power. Yup, it's an iron-rich diet, but you can keep cost down by buying surplus mil stuff.
     

     

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  18. tubino

    tubino A guy with too many tubes Subscriber

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    Oh, and if youse guys want to go with 6CJ3 or similar novar dampers, I've got the sockets you want! Ceramic & silver mil-spec! These are Canadian (NOT the Russian MAGnovar sockets for EL-509 etc with bigger pins), and they are cool and hard to find. I bought a quantity years ago...
     
  19. PakProtector

    PakProtector AK member

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    Hey-Hey!!!,
    The E-Linear amp is a reasonable option. One could follow Pete's KT88 design, or one could shrink it to EL84/6V6 level, or somewhere in the middle with 7591's. It is a very useful and forgiving design, and it can be expanded into PP( my favourite ).

    I do favour smaller for the first builds. A buy of James SE iron would be easy to orchestrate, and custom power could be had from Heyboer. Lots and lots ov options....:)
    cheers,
    Douglas
     
  20. Squidward

    Squidward Scrappy Mod Staff Member Moderator

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    Sign me up for the debugging build session. I can also take pics for an assembly manual. I also can scrounge a bunch of tubes, to help suppliment. I can especially source the OD3, and I agree: Bring on the Glow! I love that purple tube!

    In my limited experience, the most time consuming and least rewrding work can be the chassis. Having a pre-punched/drilled chassis can save hours of meticulous work.

    Count me in! :thmbsp:
     

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