Modding tube hi-fi gear for guitar? (Dynakit ST70)

Discussion in 'Amps and Cabs' started by e-flat, Jan 3, 2006.

  1. e-flat

    e-flat Supporting Member

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    How feasible is the prospect of using components from old hi-fi power amps for the basis for a guitar head? I scored an old Dynakit ST70 power amp and the matching preamp[ last year and will probably never get around to taking them to a tech for check up , etc. I would be interested in using the components for a guitar amp if the results would be worth it.... Just looking for some input regarding tone of the transformers these things used, etc.
    The ST70 came loaded with Mullard EL34s...bonus.
    Thanks for any advice.
     
  2. hogy

    hogy Member

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    I really wouldn't do it. The Stereo 70 is a classic in the tube hifi world. It sounds great and can easily be modded to sound spectacular. Same goes for the preamp.
    If you haven't listened to properly working tube hifi you're in for quite a surprise.

    This setup is worth a good bit of money already, and will only go up from here.
    Fix it up, upgrade it if you want (do a google search, there are tons of sites), buy some nice speakers for it, and enjoy.

    Don't hack it up, please.

    Hogy
     
  3. bob-i

    bob-i Member

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    Oh BABY, these are awesome amps. I'm not sure how valuable the preamp will be for guitar, but the power amp with those Mullards should be great.

    I'd use a nice tube type guitar preamp in front of the Dyna, Marshall or Peavey Rockmaster would nail it.
     
  4. pirateflynn

    pirateflynn Supporting Member

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    Hogy,

    I would love to know what mods you recommend. I just got a Dynaco St70, a pre-amp and FM tuner in excellent condition w/ the original tubes. It's being check out right now and would like it to sound as good as possible. Thank you in advance.

    Ken
     
  5. TheAmpNerd

    TheAmpNerd Member

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    If I recall wasn't the first SUNN amp an ST70 with
    a fender style pre amp?
     
  6. e-flat

    e-flat Supporting Member

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    hogy:
    Yeah, I am reluctant to really just "piece it out" . I just don't have a use for it right now.... I'm sure tube audio guys will read my post and react similarly to the way most of us would if someone talked about modding / altering a Tween Deluxe or AC15 or something .... "SACRILEGE!!!" :eek: Wish i could find someone who was into tube audio who had a nice little tube guitar amp they'd like to trade for the DynaKit preamp and Power amp (minus the Mullards, which I plan on keeping due to the fact that I will never be able to afford a quartet at the rates they bring). Is there a board where I might be able to post some sort of offer like this and see if I get bites? Like a tube hi-fi forum?
    Just wanted some input for options....If its a classic then its probably best to leave it relatively intact for someone else to enjoy.
     
  7. hogy

    hogy Member

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    It will need fresh power supply caps. I rebuilt mine with stock values, but there are upgraded power supply boards available for more filtering (you'll lose the tube rectifier).

    I put a Triode Electronics driver board in mine, that's it for mods.

    The preamp will also need basic rebuilding of the power supply, all bets are off from there. There are unlimited mods you can do, just look around the web.

    Start by going here: http://www.audioasylum.com/index.html
    and do a search in their "Vintage Gear" section, you'll find reading material for days.

    Hogy
     
  8. dbeeman

    dbeeman Gold Supporting Member

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    Please don't hack these up for guitar. Good tubes are wonderfull for Hi-Fi, and David Hafler knew what he was doing on these.

    just as aside, I do believe the output section looks similar to an Alessandro Bloodhound (the original with El84s)
     
  9. number9

    number9 Member

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    Trade... for a good ST70? Hrmmm, what are you looking for? I have owned two and
    refurbished about 10 for people... great little hi-fi amps for the bedroom/front end
    speakers. I mean, compared to new tube units, they are a great way to get a 35wpc
    amp with solid iron. Let me know what you would be willing to trade for the ST70,
    if you are interested.
     
  10. Dana Olsen

    Dana Olsen Gold Supporting Member

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    Hogy is expert in this, I am not.

    Having said that, I'm pretty sure there are a couple other amp builder types who offer 'mods' for Dynakit amps, as well as refurbing them.

    Andy Fuchs does, or used to, for example.

    As an 'analog audio' kind of guy, I strongly agree with Hogy - fix it up and use it, but don't try to mod it for guitar. Truly, if that worked well, there'd be a lot of them around now (think of all those 'Dynakits out there in the 60's) .... and there aren't.

    I tried to buy a Dynaco amp at a garage sale in Santa Barbara in '94. They were asking $20, and I offered $15 when the owner drunkenly declared he wasn't sure if he wanted to sell it after all. Hey, it was Sunday afternoon (GRIN)

    A couple days later, I saw it sitting on top of the dumpster outside the apartment complex. Guess it didn't sell. So I rescued it out of the dumpster, and found inside - an RCA 12AX7, 2 Sylvania 6V6's (one broken), and a REAL AMPEREX BUGLE BOY 12AX7 - is that cool, or what.

    I gave it all to my pal Robert - it sounds great!

    Dana
     
  11. drbob1

    drbob1 Silver Supporting Member

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    Those also make decent studio amps-not fatiguing and decent sound compared to anything else in their price range. Why not sell it on Ebay? You'd get $250-400 for it and have a nice piece of change to start saving for your Komet or Roccaforte. Before you do, though, you owe it to yourself to plug your CD player into it and run it thru a pair of stereo speakers to hear just how warm these things can be. I never listen to the big ss stereo downstairs anymore, that's for the TV. Upstairs, I listen to my vinyl on an old Scott amplifier (also got a tube CD player that sounds great to use with that-a guy mods them from ss CDs if that isn't a kick!!!!).
     
  12. pirateflynn

    pirateflynn Supporting Member

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    Thanks!
     
  13. e-flat

    e-flat Supporting Member

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    number9: Dropped you a PM.... You can email me at squatchyeti@yahoo.com

    drbob: Yeah, I've been tempted to try it out, but with all of the old caps, etc I didn't want to fire it up without getting the OK from a tech. I live in a very small town and the one "tech" in this town is a joke. I also have an old Bogen tube receiver from ages past.... I fired that up when I first got it and it sounded wonderful. I imagine the Dynakit tube pre / power combo would be excellent.
    I may ebay it, but I'd rather try to swing a trade for guitar gear.
     
  14. 83stratman

    83stratman Member

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    I haven't read the other responses to this thread, so forgive me if I am repeating something already said, but....PLEASE DON"T DO THIS! Sell the amp and pre to someone (me) and buy some parts to build an amp with...
     
  15. 83stratman

    83stratman Member

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    One more thing, this is the same as an audio dude asking, I have these two Fender tube amps, but want a stereo amp. Is it worth taking the Fenders apart and building a stereo amp?
     
  16. 83stratman

    83stratman Member

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    Depending on the condition of the ST70, I have a Peavey Classic 30 with an intermittant "POP then low output" until the amp is power cycled that is in real good shape and is most likely a bad tube or bad solder joint somewhere that I would trade for the Dynaco setup.
     
  17. TheAmpNerd

    TheAmpNerd Member

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    You don't need to.
    Just use them as mono blocks. After your Hi-Fi pre amp, use
    one Fender amp for the left channel and one Fender amp for the right channel.

    You might want to stuff the Fender with 12AU7s though.

    Have fun.
     
  18. Blue Strat

    Blue Strat Member

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    Bogen amps are better candidates for guitar conversion. This has been done numerous times before.

    The ST70 has an UltraLinear power amp which makes it great for stereo and not so great for guitar. If you really don't want the amp, I would sell it and use the cash to buy a guitar amp or something more suitable for conversion to a guitar amp.
     
  19. e-flat

    e-flat Supporting Member

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    Thanks for all of the input guys. Modding is out of the question now ;)

    I'll field any trade offers for Tweed Champ style small all tube amps for recording, boutique pedals or other stuff. I'll keep it to this post for now...maybe just try to sell it flat out if nothing comes up.

    Just to be clear - I'm DEFINITELY keeping the Mullard EL34s that are in this thing. So I'm looking to trade the unit without tubes.
     

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