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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


5 posters

    chassis voltage

    dmagazz
    dmagazz


    Posts : 147
    Join date : 2018-06-20
    Age : 54
    Location : new fairf, ct

    chassis voltage  Empty chassis voltage

    Post by dmagazz Thu Dec 30, 2021 8:18 pm

    st-70 chassis bleed question. all my caps have been upgraded including the driver board,
    also the selenium diode removed and  and diodes/caps changed to replace it.
    but the question involves the fact that ive got 40vac if i read my chassis to a ground receptacle
    in the wall. if i unplug and re-plug it the opposite way i get the same 40vac im guessing this is filter
    bleed,
    BUT - im curious if this indicates anything else. im wondering if this unit might benefit from some add on at this point.

    NOTE, if it matters to anyone
    plugged into a Gator GRR-8PL-US rack with a built in 5 plug 15a surge protector power strip.
    the rack has a 3 prong power cable to the wall
    the wall outlet is checked/correct orientation
    bias is set to 1.48 on both sides
    all OEM Dynaco stock healthy tubes

    PS I CINCERLY hope everyone had a great Christmas, or whatever holiday you might celebrate, or none
    avatar
    Dale Stevens


    Posts : 181
    Join date : 2014-07-06
    Age : 72
    Location : Loris, SC

    chassis voltage  Empty Re: chassis voltage

    Post by Dale Stevens Fri Dec 31, 2021 6:02 pm

    D, what is your preamp? Some have a R/C configured across the incoming AC for filtering . As that ages it tends to bleed over to chassis. Just a thought.

    AND; HAPPY NEW YEAR, Dale
    dmagazz
    dmagazz


    Posts : 147
    Join date : 2018-06-20
    Age : 54
    Location : new fairf, ct

    chassis voltage  Empty Re: chassis voltage

    Post by dmagazz Sun Jan 02, 2022 1:55 pm

    preamps are
    sometimes- preamp is a DH100, or
    sometimes- creative labs soundblaster SBX studio pro
    but this was measured with preamp disconnected,
    and also i see its the same no matter what preamp i use
    aPS happy new year to ya
    tubes4hifi
    tubes4hifi
    Admin


    Posts : 1729
    Join date : 2008-11-30

    chassis voltage  Empty Re: chassis voltage

    Post by tubes4hifi Fri Jan 07, 2022 2:09 am

    MAYBE it's not just your chassis, MAYBE it's your AC outlet. Neutral SHOULD be 0vac compared to ground.
    dmagazz
    dmagazz


    Posts : 147
    Join date : 2018-06-20
    Age : 54
    Location : new fairf, ct

    chassis voltage  Empty Re: chassis voltage

    Post by dmagazz Fri Jan 07, 2022 7:39 am

    well. like i said in my post, the outlet was checked and is correct
    Seamus
    Seamus


    Posts : 16
    Join date : 2020-03-17

    chassis voltage  Empty Re: chassis voltage

    Post by Seamus Wed Jan 12, 2022 12:15 pm

    It could be just potential with no drive behind it.
    Measure the current with a 1kΩ resistor in series with one of the VOM leads.
    Use clip leads. Don't hold the resistor.

    Is there any difference between the Earth to chassis and Neutral to chassis?
    peterh
    peterh


    Posts : 1613
    Join date : 2012-12-25
    Location : gothenburg, sweden

    chassis voltage  Empty Re: chassis voltage

    Post by peterh Wed Jan 12, 2022 2:26 pm

    Any amp that lacks ground connection will have it's chassie at a voltage level between the live
    and return. It's normally a very high impedance thus not dangerous but still a nuisance.

    Proper grounding ( such as a 3 wire wall connection ) will solve the issue.
    Seamus
    Seamus


    Posts : 16
    Join date : 2020-03-17

    chassis voltage  Empty Re: chassis voltage

    Post by Seamus Wed Jan 12, 2022 2:39 pm

    peterh wrote:Proper grounding ( such as a 3 wire wall connection ) will solve the issue.

    And depending on the rest of the system, possibly introduce a 'ground loop'

    dmagazz
    dmagazz


    Posts : 147
    Join date : 2018-06-20
    Age : 54
    Location : new fairf, ct

    chassis voltage  Empty Re: chassis voltage

    Post by dmagazz Wed Jan 12, 2022 9:08 pm

    1.6 AC at the smaller blade terminal, 1.8 AC at the ground terminal, 45vAC at the larger blade terminal

    incidentally to install the 3 prong cable was where i was going towards, but i don't want the ground to effect the circuit adversely. the install basically removes the death cap and allows ground to chassy why maintaining the tranny isolated correct?
    Seamus
    Seamus


    Posts : 16
    Join date : 2020-03-17

    chassis voltage  Empty Re: chassis voltage

    Post by Seamus Thu Jan 13, 2022 11:43 am

    dmagazz wrote:1.6 AC at the smaller blade terminal, 1.8 AC at the ground terminal, 45vAC at the larger blade terminal

    Were the VOLTAGE measurements across the 1kΩ resistor?
    You DO NOT want to be measuring anything relative to the line [narrow] terminal


    dmagazz wrote:incidentally to install the 3 prong cable was where i was going towards, but i don't want the ground to effect the circuit adversely. the install basically removes the death cap and allows ground to chassy why maintaining the tranny isolated correct?


    ¿Que?

    Death Cap?

    No offence, but are you certain you should be messing around with line voltages and the inside of a tube amp?
    dmagazz
    dmagazz


    Posts : 147
    Join date : 2018-06-20
    Age : 54
    Location : new fairf, ct

    chassis voltage  Empty Re: chassis voltage

    Post by dmagazz Thu Jan 13, 2022 7:44 pm


    YOU- Death Cap?

    so your unfamiliar with the term "deathcap"

    YOU- No offence, but are you certain you should be messing around with line voltages and the inside of a tube amp?

    i shouldn't be in an amp because i am familiar with the term deathcap ?

    no offence but if your gonna give advise, you should know- that capacitor pet name is given because it connects neutral to chassis for a ground and if the polarity is switched and it fails it could "SHOCK THE SHIT OUT OF YOU"!!
    and when you hook up a 3 prong cord, that cap is usually removed or it may explode if a polarity switch is in use (if there is one existing) its no longer needed as an "AC ground" if your using a ground terminal 3 prong cord.

    YOU- Were the VOLTAGE measurements across the 1kΩ resistor?

    no they were not or i would have said so.

    YOU- You DO NOT want to be measuring anything relative to the line [narrow] terminal

    my fluke is not a wire. if i test line reference to the chassis all its gonna do is tell me if good continuity exists between the common and the chassis, its NOT going to explode

    PS, im no engineer, but i am ABSOLUTLY capable.
    at this point this has gone astray. i just want to know if this phantom voltage might be caused by the chassis ground reference cap(death cap) or if that voltage is from the circuits nature and is grounded off by hooking up a 3 prong cord might it change the behavior or sound of this amp in any way. no offence, i guess i was looking for someone more insightful, not a judge. lol, don't hold the resistor SMH i mean really. :/ just forget i asked
    Seamus
    Seamus


    Posts : 16
    Join date : 2020-03-17

    chassis voltage  Empty Re: chassis voltage

    Post by Seamus Fri Jan 14, 2022 11:25 am

    Sorry.

    There is no 'death cap' in a Dynaco ST-70

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