First amp build questions

Discussion in 'Glowing Bottle Tube Amp Forum' started by mtglick, Jul 31, 2020.

  1. mtglick

    mtglick TDPRI Member

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    Hi, all--

    Longtime lurker who has benefited heavily from info and opinions here, generally in equal measure. Have a question for the amp builders around here. Ultimately, I'm looking for advice.

    I bought a nonfunctioning Fender Frontman 212r combo for next to nothing, predominantly because it had a couple of speakers in it that I could use in another cab. Either I was going to figure out how to repair it, or I was going to scrap the whole chassis and finish a different amp build in the cab.

    So, there's apparently a reason these things are DNR at Fender. Tried replacing the two big caps, plus all four transistors, and anything that looked burned. Reflowed half the board, all the pots, etc., and I'm still getting 26v DC at the speaker outs, which ate a test speaker, and one of the resistors keeps frying anyway. It may be an easy repair for some, but it's above my limited experience and toolset, especially when there are other bad ideas out there I can waste money on.

    Finally decided this morning that I'm done--this board is going in the trash, and the other project I thought would go into this cab is half an inch too long for this cab, and needs a different cab layout anyway.

    So, this leaves me with an interesting dilemma. I now have an empty, open-back 212 cab, in Fender silver and black. I have the chassis, and the PT.

    Any ideas what a novice builder could potentially do to make use of the chassis, PT, and cab? I have a Mojo 5e3 small parts kit in my pile, but that was intended for a different idea. Open to other kits/builds that are about the same level of difficulty as a 5e3 or thereabouts. Any thoughts?
     
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  2. JuneauMike

    JuneauMike Poster Extraordinaire

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    Welcome to the rabbit hole. If this is your first amp build, I'd recommend something somewhat simple, but then again you've got that nice big cabinet and a hankering to fill it. I was involved in a couple of pretty interesting discussions on Matchless amps (Spitfire was my main interest.) The layouts and schematics look pretty simple and straightforward, whoever plate voltage is a critical thing and the iron you chose becomes an important mystery to solve.

    Also, I'd suggest you post this over at Shock Brothers forum in the DIY section. Lots of builders there with great ideas on salvage possibilities.
     
  3. mtglick

    mtglick TDPRI Member

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    Thanks much, JM. Salvage amps seems to be the right term--will post over there and see what I get.
     
  4. dan40

    dan40 Tele-Afflicted

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    If you are lucky enough to find a new chassis that will mount in the cabinet properly, you can build almost any circuit you desire. I usually try to reuse the old chassis and pick a circuit to build that has the same number of tubes and control pots. This saves a lot of time on marking and drilling the new holes. If you pick a circuit that has similar tube types and operating voltages you can reuse the original transformers which will save quite a bit of money. This all takes a bit of knowledge and planning to pull off successfully though. For a first build, a kit with good instructions is much easier and will have a higher chance of working properly the first time. Be sure to check out Rob's sight for info on all things amp related if you haven't already.

    https://robrobinette.com/How_Amps_Work.htm
     
  5. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Making the chassis work for tubes will be a job unless you have step bits or socket punches or similar tools. Other than that, have at it :D If you could find a chassis that's the same width, that would be the best plan.

    Pro tip for the future - unlike tube amps, solid state amps generally don't need to see a load, so I always work on those *without* a speaker hooked up until I'm sure the output is semi-normal.
     
  6. mtglick

    mtglick TDPRI Member

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    Super helpful! Thanks much. I do still have the chassis and PT, and enough basic metalworking tools to adapt the chassis to the circuit design. Or will buy what I need. Was thinking about riveting a new faceplate (just a shaped piece of stainless) over the existing face of the amp anyway, if I needed to close off some holes. What I know for now is that I've got a chassis with two inputs to the left, then ten control pot spaces, some smaller toggle switch-sized (or adaptable) openings sprinkled among the pots, then three input jacks to the right. Lots of room in the chassis for handwiring.

    Now a bit of confession. What I failed to mention earlier is that, over the years, I've collected a really stupid number of amps for a home user. Mostly low-volume, and a few high-volume ones, tube, ss, hybrid, modeling, it's a little bit of everything. I freely admit that I have chronic GAS, which I attribute to a childhood of gear deprivation, so as I've gone along, when a good deal pops up or a broken bit of kit comes my way, I have a hard time staying away, and can usually repair the damage without too much difficulty. To date, my guitar amp roster is as follows, in no particular order (well, other than the way they're stacked up here):

    H&K Tubemeister 18
    VHT Special 6 Ultra
    Blackheart Little Giant
    Fender Champ 100
    Fender Super Champ X2
    Fender Princeton Chorus
    Fender Mustang V2.1
    Orange Dark Terror
    Randall RD5C 1x10
    Vox MV50AC
    Vox NT2
    Vox NT15(I went through a phase)
    Vox NT50
    Vox VT20X (for a long time)
    Kustom Defender 5HMOD
    Marshall AVT20 1x10
    Marshall 100 HCFX
    Monoprice Stage Right 15
    Peavey Windsor
    Peavey Heritage VTX 2x12
    Randall RH150G3
    Egnater Tourmaster 2x12
    Blackstar Fly3 (stereo)
    Yamaha THR10c
    ...and a Hog 20 with a bunch of mini Hotone pedals that I'm bolting onto it, for important travel purposes so I can annoy my kids on long road trips.

    Most of these have been modded or upgraded--speakers, tubes, some new resistors, etc. About half of these came to me in nonworking order, and needed some service, or love, or other help, and nearly all of them were at or around $100-$150 to acquire, with a few notable exceptions. I've also got a 5e3 small pieces kit that's going into a different headshell I've got lying around from a dead Crate V33, and Kustom 72 coupe in pieces on my bench, which doesn't quite fit into the cab, and would need to be trimmed, plus the cab trim for the controls, so that's going to get its own cab someday.

    But I know. It's a problem. And I'm not gonna talk about the pedal collection, or the bass amps, or the guitars built and/or repaired. There are limits.

    Back on topic. I fully realize that most of these aren't everybody's cup of tea, and a lot of them are one-trick ponies, but I have fun with 'em--usually, if I can't get what I want from one of them, well, there are six or seven other options. Fixing broken stuff and following schematics is generally in my skillset, but I've been concerned about taking on a full build because my electrical theory is a little weak, and my soldering is similarly so-so. I'm hoping to find something relatively easy to build up in stages, where I can stop and start as needed over time without losing track of what I'm doing.

    What I'm looking for now is to take the plunge and find a kit that I can build and bolt into the Fender chassis and 2x12 cab, potentially in the middleweight (30-60w) category, that has more of the 6l6 DR clean, with enough headroom to play clean-ish with a drummer, but without being too sterile. Reverb would be nice.
     
  7. dan40

    dan40 Tele-Afflicted

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    You got the GAS bad...lol! I have quite a few old combos myself that I have collected for future builds. I can't justify the expense of many of the higher end amplifiers since I'm strictly a home player but I do like to clone many of them in these old amp chassis I have collected.

    The Frontman sounds like it would be a good candidate for a Blackface circuit. With your past experience of repairing those amplifiers you would likely do just fine building a Fender circuit from any of the layout pics found online. Material list are also readily available online for these circuits.
     
  8. tubegeek

    tubegeek Friend of Leo's

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    @mtglick - a word to the wise - stainless is almost impossible to drill without a "real" drill press and pro bits. Joe Handyman cordless drill user? Stay away.
     
  9. mtglick

    mtglick TDPRI Member

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    'Preciate the warning, TG. Have a press and a reasonable index of carbides. Cover it, clamp it, cool it. Obviously I'd rather not have to deal with it, could look at just some aluminum as well, depends on the # of holes and how ambitious I'm feeling.
     
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