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    Dynaco ST-35: My experience buying and restoring.

    crkohut
    crkohut

    Posts : 22
    Join date : 2016-11-02
    Age : 58
    Location : Sudbury, Ontario, Canada

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    Post by crkohut on Sat Feb 09, 2019 8:35 am

    Hello everyone,
    Just wanted to share my experience buying and restoring a vintage ST-35. Being a complete newbie, at the time, to tube amps and electronic restorations I thought that perhaps my experience could inspire others (novice) to take the plunge into tube gear.

    I'm still novice for sure, but i think if I can do it, hopefully the right way, that others like me could as well.

    Here is a link to my YouTube playlist for the Dynaco ST-35 showing my experience from unboxing, standard upgrades to ensure reliability and then ultimately a complete restoration (novice style...   study  )

    ST-35 Playlist

    Enjoy,
    Rob

    PS: Certainly willing to hear any criticisms that may be helpful. Smile

    Disclaimer: I may or may not really know what I am doing. This is NOT meant to be instructional and your results may differ. If you are unfamiliar with electronic components and their dangers please do not open, change or touch any circuits on any electronic component. confused
    Peter W.
    Peter W.

    Posts : 1361
    Join date : 2016-08-07
    Location : Melrose Park, PA

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    Post by Peter W. on Mon Feb 11, 2019 2:53 pm

    First of all - whereas I may not entirely agree with your means-and-methods - which is more stylistic than of substance - I really have only one quibble (so far, and on Part 2 & 3) which is your advocacy and installation of a 3-wire line cord, with a ground directly to the chassis.

    Second I am impressed with the level of detail and care displayed. Many could learn from it.

    The entire issue of 2 vs. 3 wire line cords has been discussed to death on other threads herein. As I note, it is a quibble, not a condemnation of the practice. I prefer using a polarized 2-wire cord - or a non-polarized cord, if, like me, you are plugging that amp into another component that does not accommodate polarized plugs. But the PAS does have a polarized plug and I have marked the rear receptacles as to which is hot and which is neutral.

    Curious - have you done other equipment since? Not necessarily Dynaco, but other tube stuff? Has your bench evolved?

    Thank you for the post and links!
    crkohut
    crkohut

    Posts : 22
    Join date : 2016-11-02
    Age : 58
    Location : Sudbury, Ontario, Canada

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    Post by crkohut on Mon Feb 11, 2019 3:50 pm

    Peter W. wrote:First of all - whereas I may not entirely agree with your means-and-methods - which is more stylistic than of substance - I really have only one quibble (so far, and on Part 2 & 3) which is your advocacy and installation of a 3-wire line cord, with a ground directly to the chassis.

    Second I am impressed with the level of detail and care displayed. Many could learn from it.

    The entire issue of 2 vs. 3 wire line cords has been discussed to death on other threads herein. As I note, it is a quibble, not a condemnation of the practice. I prefer using a polarized 2-wire cord - or a non-polarized cord, if, like me, you are plugging that amp into another component that does not accommodate polarized plugs. But the PAS does have a polarized plug and I have marked the rear receptacles as to which is hot and which is neutral.

    Curious - have you done other equipment since? Not necessarily Dynaco, but other tube stuff? Has your bench evolved?

    Thank you for the post and links!

    Thanks for all the good words, Peter.

    The plug opinion certainly makes sense. I guess I grasped onto one reason to put a grounded plug and believed it... :-)

    No I have not worked on any other tube stuff. My only other experience is with some Chinese clock kits and the like to practice board soldering.

    I have just ordered two M-125 mono blocks yesterday.... :-) I'm really looking forward to assembling these great amps and intend to do some videos of the whole process. Stay tuned, I'll post them here as they are uploaded.

    Thanks again.
    peterh
    peterh

    Posts : 1211
    Join date : 2012-12-25
    Location : gothenburg, sweden

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    Post by peterh on Mon Feb 11, 2019 4:58 pm

    My experience is that grounding amps together will reduce hum, especially if one can
    connect to a real ground.
    What sometimes bites is that there could be several ground(s) , that floats on different potential,
    and this will introduce hum. Cable-tv coax is one, using several outlets another.
    Grounding amps will also reduce the risk for electrocution.
    ( a contradiction is servicing, here sitting on a isolated rubber mat, and no real ground for
    device under test and instruments ( but all interconnected) reduces the danger if one accidently
    touches a live cable) . An ground fault interrupter ( which has nothing to do with ground) is mandatory. But this practice is illegal for employees in sweden. I do it for myself anyway)
    The above setup does not prevent danger from B+ however, thus one should not work alone
    instead a mate in the neighborhood that knows heart resurrection :-)

    ( ground fault interrupter works by comparing current in one lead with the current in the other. If
    any differences , usually by leakage to ground, will cut the power. Sensitivity a few mA !)
    Peter W.
    Peter W.

    Posts : 1361
    Join date : 2016-08-07
    Location : Melrose Park, PA

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    Post by Peter W. on Mon Feb 11, 2019 5:13 pm

    Here is where there may be some basic misunderstandings in terms.

    peterh wrote:My experience is that grounding amps together will reduce hum, especially if one can
    connect to a real ground.  
    AMEN to that! I am blessed to live in a house with a 1930-style hydronic cast-iron radiator system. Code requires a  hard connection to a proven ground - typically the domestic water service. In our case that, and two ground-rods. 4" cast-iron mains filled with inhibitor-laden water are excellent conductors.

    What sometimes bites is that there could be several ground(s) , that floats on different potential,
    and this will introduce hum. Cable-tv coax is one, using several outlets another.

    Absolutely. And why the main Ground must be at the lowest potential in all cases. BUT....


    Grounding amps will also reduce the risk for electrocution.

    Current will flow 'downhill' and is entirely indiscriminate as to which direction that might be. The main system ground must be verified, or it will increase the potential for shock by raising the chassis above the neutral in some extreme cases. A VERY bad thing.

    ( a contradiction is servicing, here sitting on a isolated rubber mat, and no real ground for
    device under test and instruments ( but all interconnected) reduces the danger if one accidently
    touches a live cable) .

    A few things: Concrete floors are quite conductive, and basement floors are the worst. After which are reinforced concrete floors in metal-pan subfloor. Any servicing tech must not rely on a rubber mat or any other passive device. And why it is I advocate for an isolation transformer to be used for service work, especially diagnosis.

    An ground fault interrupter ( which has nothing to do with ground) is mandatory. But this practice is illegal for employees in sweden. I do it for myself anyway)
    The above setup does not prevent danger from B+ however, thus one should not work alone
    instead a mate in the neighborhood that knows heart resurrection :-)

    A GFIC device, as with an Isolation Transformer, is one more step in general safety. But working with an Iso really does make things safer. Not 100% by any means, but MUCH safer than without. NOTE: Use only a medical-grade or industrial grade device. Cobbling two conventional transformers back-to-back is simply not a good idea. Perhaps better than nothing, but only perhaps.

    ( ground fault interrupter works by comparing current in one lead with the current in the other. If
    any differences , usually by leakage to ground, will cut the power. Sensitivity a few mA !)

    Just be safe. If one does not have an isolation transformer, and one cannot work on a proven non-conductive surface, leave one hand in your back pocket, and have an AED on-hand together with an individual to use it.

    Best of luck!

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