ST-70.

tonyp063
tonyp063 Posts: 1,083
in 2 Channel Audio
So this followed me home. Can I keep it? :-)

Yes. Much work to be done. Starting with canned air!
I'm trying to decide if I want to keep it as "stock" as possible or go with the known upgrade/modification bits.

Comments, critiques, suggestions & opinions welcome.

In the meantime I've got documentation & am getting my read on.
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Comments

  • mhardy6647
    mhardy6647 Posts: 33,801
    edited April 2019
    5i8814u6bs98.png
    source: www.alliedcatalogs.com (1968)

    If you want to (really) enjoy it, you should probably replace everything except the iron. :/
    The driver stage of that amp in particular (IMO and FWIW) is a major impediment.
    The P/S also likely needs attention (unless it's been rehabbed in the last 5 or 10 years).
    If it is all original -- congratulations, you just acquired a hobby!

    ;)

    Here I was wondering -- perhaps even hoping -- you'd scroed (as some folks on AK might say) an ST70, instead of an ST70 :p

    12117029523_d31078860f_b.jpgST70 by Mark Hardy, on Flickr

    Actually, these rascals, as originally designed, are something of a hobby, too. :)

    kyic3w4t0lgl.png

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  • mhardy6647
    mhardy6647 Posts: 33,801
    edited April 2019
    Oh, BTW -- that EL34 on the back left is bad :( Air's gotten into it and oxidized the getter from barium to barium oxide (in case you didn't know that already).

    qyogix2e9dvg.jpg


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  • Faustin
    Faustin Posts: 1,149
    "Oh, BTW -- that EL34 on the back left is bad :( Air's gotten into it and oxidized the getter from barium to barium oxide (in case you didn't know that already)."

    Picky, picky, picky. :D

    Yes - nice little project
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  • mhardy6647
    mhardy6647 Posts: 33,801
    It's too bad, too, as it looks like it was a "real" British one :|

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  • tonyp063
    tonyp063 Posts: 1,083
    edited April 2019
    Mark,
    Yes. I did know that Real British Mullard lost it's Magic Smoke(tm). I'm not happy about that.
    But.
    The amp was free. From my late father's stash.

    I'm going to clean it up, obviously & do a cap & selenium rectifier replacement.
    Get a sense of what it sounded like. I've sourced a proper replacement so I can hear it with all 60's Mullards.
    I'll see where it goes from there.

    And yes, I did buy throw-away tubes for to when I test my work.
    If it is all original -- congratulations, you just acquired a hobby!

    Oh lord, I am *well* aware of that possibility. We shall see.

    It''s bone stock as the day it left New Jersey.
    I don't know where dad got it, but I never saw it as a kid.

    And I can verify that tubes glow & sounds happen, after a *careful* powerup.
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  • mhardy6647
    mhardy6647 Posts: 33,801
    edited April 2019
    You'll probably have to replace both tubes in that channel for best results.
    I don't remember offhand what bias topology that amp uses (and, not surprisingly, as I type this I am too lazy to look it up :( ) but I reckon a matched pair of EL34s in at least each channel is a requisite.

    Good that it works :) A PP amp with one output tube can sound remarkably not bad -- but it is not good for 'em to run thus so unbalanced.

    You likely know that already, though.

    Do you have the docs for it? Easy enough to find if you don't (but, again, you likely knew that too).

    The ST70 stock is a good amp. It is not a great one, but that doesn't diminish its capacity. The iron in it is good and is where the value lies.

    Of course, that Mullard 5AR4 is a nice value-add, too ;)
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  • tonyp063
    tonyp063 Posts: 1,083
    It is a nice thing.
    And the EL34's read xf2 - with codes that tell me 1960.

    I've got an online source for the docs, a soldering setup & a Mouser account. Stand back

    Fire in the hole!
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  • verb
    verb Posts: 10,176
    Looks like a nice project! Actually pretty clean underneath! I would keep it, and get that baby running! Looks like we have plenty or folks here familiar with it, and perhaps help with modding it a bit! Have fun! :smile:
    Basement: Polk SDA SRS 1.2tl's, Cary SLP-05 Pre with ultimate upgrade,McIntosh MCD301 CD/SACD player, Northstar Designs Excelsio DAC, Cambridge 851N streamer, McIntosh MC300 Amp, Silnote Morpheus Ref2, Series2 Digital Cables, Silnote Morpheus Ref2 Series2 XLR's, Furman 15PFi Power Conditioner, Pangea Power Cables, MIT Shotgun S3 IC's, MIT Shotgun S1 Bi-Wire speaker cables
    Office: PC, EAR Acute CD Player, EAR 834L Pre, Northstar Designs Intenso DAC, Antique Sound Labs AV8 Monoblocks, Denon UDR-F10 Cassette, Acoustic Technologies Classic FR Speakers, SVS SB12 Plus sub, MIT AVt2 speaker cables, IFI Purifier2, AQ Cinnamon USB cable, Groneberg Quatro Reference IC's
    Spare Room: Dayens Ampino Integrated Amp, Tjoeb 99 tube CD player (modified Marantz CD-38), Analysis Plus Oval 9's, Zu Jumpers, AudioEngine B1 Streamer, Klipsch RB-61 v2, SVS PB1000 sub, Blue Jeans RCA IC's, Shunyata Hydra 8 Power Conditioner
    Living Room: Peachtree Nova Integrated, Cambridge CXN v2 Streamer, Rotel RCD-1072 CD player, Furman 15PFi Power Conditioner, Polk RT265 In Wall Speakers, Polk DSW Pro 660wi sub
    Garage #1: Cambridge Audio 640A Integrated Amp, Project Box-E BT Streamer, Polk Tsi200 Bookies, Douglas Speaker Cables, Shunyata Power Conditioner
    Garage #2: Cambridge Audio EVO150 Integrated Amplifier, Polk L200's, Analysis Plus Silver Oval 2 Speaker Cables, IC's TBD.
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  • mhardy6647
    mhardy6647 Posts: 33,801
    I am assuming he's gonna keep it! :)
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  • verb
    verb Posts: 10,176
    mhardy6647 wrote: »
    I am assuming he's gonna keep it! :)

    Yep. And counting on your tutelage! :smile:
    Basement: Polk SDA SRS 1.2tl's, Cary SLP-05 Pre with ultimate upgrade,McIntosh MCD301 CD/SACD player, Northstar Designs Excelsio DAC, Cambridge 851N streamer, McIntosh MC300 Amp, Silnote Morpheus Ref2, Series2 Digital Cables, Silnote Morpheus Ref2 Series2 XLR's, Furman 15PFi Power Conditioner, Pangea Power Cables, MIT Shotgun S3 IC's, MIT Shotgun S1 Bi-Wire speaker cables
    Office: PC, EAR Acute CD Player, EAR 834L Pre, Northstar Designs Intenso DAC, Antique Sound Labs AV8 Monoblocks, Denon UDR-F10 Cassette, Acoustic Technologies Classic FR Speakers, SVS SB12 Plus sub, MIT AVt2 speaker cables, IFI Purifier2, AQ Cinnamon USB cable, Groneberg Quatro Reference IC's
    Spare Room: Dayens Ampino Integrated Amp, Tjoeb 99 tube CD player (modified Marantz CD-38), Analysis Plus Oval 9's, Zu Jumpers, AudioEngine B1 Streamer, Klipsch RB-61 v2, SVS PB1000 sub, Blue Jeans RCA IC's, Shunyata Hydra 8 Power Conditioner
    Living Room: Peachtree Nova Integrated, Cambridge CXN v2 Streamer, Rotel RCD-1072 CD player, Furman 15PFi Power Conditioner, Polk RT265 In Wall Speakers, Polk DSW Pro 660wi sub
    Garage #1: Cambridge Audio 640A Integrated Amp, Project Box-E BT Streamer, Polk Tsi200 Bookies, Douglas Speaker Cables, Shunyata Power Conditioner
    Garage #2: Cambridge Audio EVO150 Integrated Amplifier, Polk L200's, Analysis Plus Silver Oval 2 Speaker Cables, IC's TBD.
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  • tonyp063
    tonyp063 Posts: 1,083

    I am assuming he's gonna keep it! :)

    d@mn skippy he is!




    Yep. And counting on your tutelage! :smile:

    and d@mn skippy he is :-)
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  • tonyp063
    tonyp063 Posts: 1,083
    Small, successful steps.
    Coupling, bias & PS caps have been replaced. Selenium rectifier replaced with a diode. Rectifier tube has had diode protection added.

    Smoke test passed!
    All the Magic Smoke has stayed where it belongs.
    Bias holds rock steady after a 10 minute warm up. Tubes are Russian things, just in case of operator error. The Mullards will stay put away for a while

    I deem this worth the effort moving forward. First a *thorough* cleaning & then to listen for a while.

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  • maxward
    maxward Posts: 1,577
    That is looking great.
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  • codycatalist
    codycatalist Posts: 2,662
    It is looking good indeed. Nice job!
    Just a dude doing dude-ly things

    "Temptation is the manifestation of desire which equals necessity." - Mikey081057
    " I have always had a champange taste with a beer budget" - Rick88
    "Just because the thread is getting views don't mean much .. I like a good train wreck doesn't mean i want to be in one..." - pitdogg2
    "Those that don't know, don't know that they don't know." - heiney9
    "Audiophiles are the male equivalent of cat ladies." - Audiokarma Member
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  • tonyp063
    tonyp063 Posts: 1,083
    Heh.
    It's looking like an old gal in need of some work right now :-) but I'm enjoying doing it.

    And this hobby is about having fun, right?
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  • mhardy6647
    mhardy6647 Posts: 33,801
    did you put the Orange Drops in?
    Yeah, I have always used the Rooskie EL34s as cannon fodder tubes on those rare occasions when I've been rehabbing an EL34 amp. Better safe than sorry :)

    Looking Good as the late Freddie Prinze was wont to say.
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  • tonyp063
    tonyp063 Posts: 1,083
    Yup.
    Orange drops are what the "gettin' my learn on" led me to use.
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  • mhardy6647
    mhardy6647 Posts: 33,801
    I put Orange Drops in my HF-81 and have absolutely no complaints. The audiophiles kind of chuckle condescendingly when they see 'em, but they're good quality, good sounding and reasonably priced coupling capacitors.

    Heck, even the IC "Lemon Drops" are very decent.
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  • tonyp063
    tonyp063 Posts: 1,083
    More steps.
    Spent a lot of time with the "Make sure Tony's soldering skills stand the test of time" sacrificial tubes (EH el-34s) and I've decided that I'm going to give this a goodly amount of time in "stock" condition before I consider modifying it.

    The OEM Mullards are of *much* better sound quality than the EH, but I want to see what else might sound interesting. And be judicious with the OEMs too.


    Research led me to get these to try. Bias dropped appropriately.

    I am not displeased.

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  • soundfreak1
    soundfreak1 Posts: 3,414
    My little girl.hb0zqr1pmqu0.jpg
    Main Rig:
    Krell KAV 250a biamped to mid/highs
    Parasound HCA1500A biamped to lows
    Nakamichi EC100 Active xover
    MIT exp 1 ic's
    Perreaux SA33 class A preamp
    AQ kingcobra ic's
    OPPO 83 CDP
    Lehmann audio black cube SE phono pre, Audioquest phono wire (ITA1/1)
    Denon DP-1200 TT. AToc9ML MC cart.
    Monster HTS 3600 power conditioner
    ADS L1590/2 Biamped
    MIT exps2 speaker cable
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  • gidrah
    gidrah Posts: 3,049
    She's a pretty one. Try this one on the top of the 1590s. I ran my ST70 on the top of 1530s. Yeah, that was sweet.
    Nice work.
    Make it Funky! :)
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  • soundfreak1
    soundfreak1 Posts: 3,414
    gidrah wrote: »
    She's a pretty one. Try this one on the top of the 1590s. I ran my ST70 on the top of 1530s. Yeah, that was sweet.
    Nice work.
    It is one of the nicest one I've seen in many years. Bought from original owner. Pretty much stock, other than the orange drops and the selenium rectifier of course.
    Main Rig:
    Krell KAV 250a biamped to mid/highs
    Parasound HCA1500A biamped to lows
    Nakamichi EC100 Active xover
    MIT exp 1 ic's
    Perreaux SA33 class A preamp
    AQ kingcobra ic's
    OPPO 83 CDP
    Lehmann audio black cube SE phono pre, Audioquest phono wire (ITA1/1)
    Denon DP-1200 TT. AToc9ML MC cart.
    Monster HTS 3600 power conditioner
    ADS L1590/2 Biamped
    MIT exps2 speaker cable
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