Anyone familiar(?): AXL Akita AT40- 212 combo, 4 el84 and 4 12ax7

Discussion in 'Glowing Bottle Tube Amp Forum' started by ecdarby, Jul 21, 2019.

  1. ecdarby

    ecdarby TDPRI Member

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    Greetings! Im hoping somebody might be able to help with any available info or experience you might have with this amp.

    I picked this up yesterday from my favorite local mom and pop music store, Competition Music in Fort Worth. They sold it to me cheap enough that it was a no brainer, even if it is an unknown Chinese made tube amp with no speakers (they were there, but part of the deal was that I would remove them and take it unloaded. They were nothing noteworthy.)

    So now that I have this home and can find almost no useful information on it, would anyone here have insight into

    -What the design is based off of (Ive seen it mentioned as being the same amp as the VHT Lead 40 and at least one other, rebadged and different cosmetics. Confirm?)

    -What impedence the internal speaker tap expects to see (there were two 12's in parallel with no impedence markings or wattage ratings).

    -It has both an 8 and 16 ohm external tap, do these defeat the internal speakers and would they be 8/16 ohms independent of the internal speakers, or calculated as total impedence with the internal speakers in parallel with the external load?

    - Fixed or Cathode bias?

    - generally worth the time to fix up and use?

    I need another 80lb 212 like I need a torn rotator cuff. But for $80, it seemed like a no brainer. But those who know me know I do love a bargain. ;)
     
  2. nixdad

    nixdad Tele-Meister

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    Yeah, that's throw away money.
     
  3. ecdarby

    ecdarby TDPRI Member

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    also, Ive never encountered this type of fading on the screenprinting of modern power tubes. Is it indicative of overheating/ some sort of internal issue, or nothing to worry about?
     

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  4. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    That looks very much like heat. It could be extended use, or it could be indicative of something nasty. I had a JJ in a small, poorly vented amp that I accidentally left running for a few days ( single ended, ran hot ). The paint was still red.

    Have a look at the guts of the amp for charred resistors, blebbed capacitors and other nastiness. It may have been sold unloaded cheap for a very good reason.

    Oh, pictures!. Of the amp in general and gut shots. It may help identifying it.
     
  5. ecdarby

    ecdarby TDPRI Member

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    Thanks man. Ive got enough speakers laying around that if I can get it working without putting much else into it, it would be worth it just to pass along to a student or someone just starting out. Really interested in information regarding specs and maybe anecdotal comments about living with one and maybe having tried it with other speakers.
     
  6. ecdarby

    ecdarby TDPRI Member

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    Definitely a couple of fuses blown coming off of two taps on the PT, some charing around the pins of the tube sockets (not sure whether that is just crappy soldering or actual damage. Ill have to really take it apart to see the traces on the underside), no discernable char smell inside the chasis or burnt up components visible on the topside of the board. None of the caps look distended or physically leaking, but I would probably replace them anyway, even if they are in spec.

    There definitely seems to be something going on with half of the output section, judging by the faded screening on the pair of 84s on the left. wonder if its maybe just a biasing issue or if something actually failed.

    The solder work is definitely not confidence inspiring. And there sure are a bunch of 4558d's in there for it to have that many tubes in it.
     

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  7. ecdarby

    ecdarby TDPRI Member

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    20190721_130622.jpg 20190721_122610.jpg 20190721_122327.jpg 20190721_122554.jpg 20190721_122518.jpg
     
    Last edited: Jul 22, 2019
  8. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    The two IC' on the heatsink. Are they voltage regulators?. The capacitors near them look to have swollen the tops a little. If they're just 7812/7912 or of the ilk, they'll be the load/ripple reject/filters and of little consequence. Could just be a trick of the light. A pair of 78xx/79xx like that can be used to generate +/- voltages for op-amps far more stably than coming straight from a transformer alone. Op-amps get used for all manner of things. I like op-amps. They work, they're easy, they're reliable, fuss free silicon worker ants in the audio chain. Far cheaper to implement a reverb drive and recover or FX loop in op-amps than in just about any other way. Many companies use them. Laney, Fender, Marshall and Vox to name a few. They power so many overdrives too. Given the number of valves in that amp, and the number of op-amps, I'd hazard a guess ( and without a schematic, it's all it is ) that the majority of them are given over to those functions, with perhaps some offering a little kick to the overdrive side of things.

    The soldering for the sockets for V6&8 looks like it has been subject to a ( poor ) rework. The shape of the solder hints that whoever did it either did it in a rush or was perhaps short in the competence region. That looks ruddy awful. The ring around the joints may just be flux bleed. Whatever, they need redoing properly. During class, if any of us made a solder or welded join like that, resemblant of bird excrement, our lecturer would enter a phase of conniptions.

    Which taps have failed fuses?, and is that a bias pot in one of the pictures?, is it really cranked hard to one end?.

    I'm guessing it's the two T1A fuses. There looks to be a bridge rectifier laid out close by with some localised heating evident. 1N4007 diodes are ten a penny, and you may wish to consider snubber caps.

    If the output transformer and power transformer meter out in a reasonable manner, I foresee a light bulb limiter in your future. I suspect someone tried to rebias it before they possessed a clue, redplated a pair, which took the fuses out, but it'd be worth careful examination and if that is a bias pot, setting it to halfway to begin with. There could be a cap out which may be the root cause.

    If nothing else, you've got a nice looking cabinet and hopefully some transformers for a sweet home brew at a chump change price.

    ps Ebay bias probes are worth their cost. Three multimeters and a pair of probes makes for accurate measurement.
     
  9. ecdarby

    ecdarby TDPRI Member

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    Thank you very much for the thoughtful reply.

    The two ic's are L7815cv 15v regulators, probably for the opamps as you suggested.

    One of the blown fuses is a T1A (FS6, second from the left) and the other is labled T100ma (FS4, at the top). And the smaller cans by the fuses are actually bulging a little.

    Also, that is a bias pot cranked hard right, so you may be correct in your assessment, very much appreciated!!!

    Unfortunately, Ive got two shows this evening to get to, but I will follow up later tonight or tomorrow. Hopefully the trannys do ohm out, and Ive been looking for an excuse to buy some bias probes.

    Ill post back as soon as I can, thank you for sharing your wisdom!
     

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  10. chrisA

    chrisA NEW MEMBER!

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    2 of these here for a fix..both the same..no preamp heaters and silence.. These were AXL amps made in China..AXL.Akita 40..VHT Lead 40..Sound City SC40..Johnson 40..and probably many others. Few years run..then disappeared. Schematic available..but no help.!..buggy bit seems to be the DCV preamp valve heaters and a mute circuit...
     
  11. chrisA

    chrisA NEW MEMBER!

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    Having read your post again..the 7815 regs also do the preamp heaters on a voltage double sort of thing..
     
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