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    Virgin Voyage - VTA ST-120 kit build

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    sKiZo

    Posts : 1504
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Virgin Voyage - VTA ST-120 kit build

    Post by sKiZo on Fri Oct 05, 2018 4:10 pm

    StevieRay wrote:

    Hey Skizo, what about putting CL90's in series (or CL80's for that matter)?  Would that not 'share the load' as far as amperage and heat?  Total heat and amps is still the same, but spread out more (between 2 devices)?  Or would they BOTH get as hot, lol?

    And wouldn't this actually drop more voltage, by using 2 in series?

    I'm about to build a ST-120 with solid-state rectifier, and am looking for a way to reduce line voltage a little without using a bucking transformer.  I'm going to use a TDR board, and use the Weber WS1 that has a thermistor built-in also.

    I suppose that would spread the load, but I never saw the need. As far as heat dissipation goes, that should also help some, but fitting two in the chassis while still providing adequate clearance to other components might be difficult. I'm thinking they might run a bit cooler, but not enough to make much of a difference.

    And I'm sure someone will correct me if I'm wrong, the WS1 does NOT have a thermistor built in. Only real complaint I've heard about the WS68 is they run HOT, and that's because of the thermistor in the can. I've seem where folk pop off the top and drill some holes in the sides top and bottom to get better air flow, and that seems to help longevity. Never a problem here, but my custom chassis allows a lot more air circulation.

    ** PS - I don't expect you'd see any more significant decrease in line voltage, as two should ramp up and level out the same ... but then, I just took a bunch of drugs and my brain ain't into the whole thinking thing right now ...

    (ooohhh ... squirrel!!) clown

    StevieRay

    Posts : 20
    Join date : 2009-01-09
    Age : 56
    Location : Central VA

    Re: Virgin Voyage - VTA ST-120 kit build

    Post by StevieRay on Fri Oct 05, 2018 4:41 pm

    The Weber WS-1 has the option to add a thermistor for $2.50 more.  You choose on their website.  No dropping resistor, just the thermistor and of course some cheap diodes.

    'Damn shame it costs $20 but it looks nicer than an empty ice cube relay with parts soldered up in it....

    I thought the WS68 got so hot because some power resistors are dropping volts to simulate a tube voltage drop.
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    dalemurray

    Posts : 26
    Join date : 2018-09-25
    Location : Wheaton Illinois

    Re: Virgin Voyage - VTA ST-120 kit build

    Post by dalemurray on Fri Oct 05, 2018 5:46 pm

    StevieRay wrote:By the way, another extremely helpful troubleshooting dialog......many, many thanks to all of you!

    Speaking of troubleshooting, Bob called back and managed to troubleshoot my issue from another time zone. My line voltage coming in to the house is over 120 volts; it measures in at 123.5-124 volts.

    He suggested I get a variac to control my line voltage. He mentioned there is a thread somewhere on the forum where a person addressed this issue with an additional transformer - or something like that.

    I am open to ideas and suggestions.
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    sKiZo

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    Re: Virgin Voyage - VTA ST-120 kit build

    Post by sKiZo on Fri Oct 05, 2018 6:30 pm

    I figure he's talking about building and using a "bucker", or bucking transformer. I've got one here that I built out of the scrap bins ...



    Re-purposing an old power strip is nice as it already has a breaker and power switch. Here's what it looks like inside, and you can find about a bazillion links on google.



    DO make sure the transformer is rated for the full load. I was lucky enough to find an old Hammond transformer that was perfect for this. My line voltage is fairly constant, so I just leave it in line all the time.
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    dalemurray

    Posts : 26
    Join date : 2018-09-25
    Location : Wheaton Illinois

    Re: Virgin Voyage - VTA ST-120 kit build

    Post by dalemurray on Fri Oct 05, 2018 6:44 pm

    I believe you hit the nail on the head with bucking transformer. Seems like it would be cheaper than a variac. I am super annoyed I may not get this running until next week. Its going to kill me to be at work and not listening to it.


    StevieRay

    Posts : 20
    Join date : 2009-01-09
    Age : 56
    Location : Central VA

    Re: Virgin Voyage - VTA ST-120 kit build

    Post by StevieRay on Fri Oct 05, 2018 7:35 pm

    I’m in the same situation; line voltage ~124 vac AND I want to use solid state rectifier.

    Variac is cheaper (5 amp) than the bucking trans UNLESS you have the scraps laying around.

    Nice ones on eBay made for this exact thing are $100.  5A Chinese variac might be $50 — if you don’t wanna burn your house down.

    That’s why I don’t wanna use either one:  too much $$$ or burn my house down.  I’ll try thermistors in the line AND the copper cap, measure my B+ and go from there....and use them other things if needed.
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    dalemurray

    Posts : 26
    Join date : 2018-09-25
    Location : Wheaton Illinois

    Re: Virgin Voyage - VTA ST-120 kit build

    Post by dalemurray on Fri Oct 05, 2018 9:35 pm

    Variac? Check.
    Diodes installed on the rectifier circuit? Check.
    New tubes ordered? Check.

    If amazon does not fail me I should be up and running again tonight.

    The over voltage is what I get for being the first house off the transformer behind the house. If I were a few houses away I would likely be just fine due to line drop.
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    peterh

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

    Re: Virgin Voyage - VTA ST-120 kit build

    Post by peterh on Sat Oct 06, 2018 2:31 am

    For those with high mains voltage AND accepts solid-state rectifiers there is a solution!
    The 5V winding is unused, and it's well insulated. Connect this in series with the 117V primary
    and you will subtract or gain 5V ac depending on the direction of the 5V winding. I suggest
    you remove all tubes and rectifier and measure the filament voltage to figure out which way to
    connect the 5V winding.


    StevieRay

    Posts : 20
    Join date : 2009-01-09
    Age : 56
    Location : Central VA

    Re: Virgin Voyage - VTA ST-120 kit build

    Post by StevieRay on Sat Oct 06, 2018 10:59 am

    If anyone has a diagram of this, please submit.

    Is this true for new transformers in the kit, or just old ones, or vice versa?

    AND if the windings are present in the VTA ST70/120, is it blessed by Bob and Roy?

    What are/were the windings for?
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    peterh

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

    Re: Virgin Voyage - VTA ST-120 kit build

    Post by peterh on Sat Oct 06, 2018 11:02 am

    StevieRay wrote:If anyone has a diagram of this, please submit.

    Is this true for new transformers in the kit, or just old ones, or vice versa?

    AND if the windings are present in the VTA ST70/120, is it blessed by Bob and Roy?
    Yes, the 5V windings are present in all transformers that has a 5V tube rectifier of the
    5ar4/5u4 class. And this winding is isolated as it is intended to carry full B+ voltage.
    One condition however is that it can only be used for this purpose if one does not use
    a tube rectifiers, it's mutually exclusive !

    StevieRay

    Posts : 20
    Join date : 2009-01-09
    Age : 56
    Location : Central VA

    Re: Virgin Voyage - VTA ST-120 kit build

    Post by StevieRay on Sat Oct 06, 2018 11:22 am

    Understood, and no doubt that winding can handle the current.

    Still, any simple diagram is appreciated — I pretty proficient with electronics, but am very visual.  I sure don’t wanna burn a new transformer up!

    You must be talking about those yellow wires from power transformer, originally white wires in Dynaco schematic?
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    CletusB

    Posts : 191
    Join date : 2018-02-11
    Age : 63
    Location : Trinidad & Tobago

    Re: Virgin Voyage - VTA ST-120 kit build

    Post by CletusB on Sat Oct 06, 2018 12:07 pm

    This old fart been using 60/40 for over half a century! What a Face

    .....and right now, my bench looks like this: Shocked    .......but it puts bread on the table, and full of nice "toys".
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    dalemurray

    Posts : 26
    Join date : 2018-09-25
    Location : Wheaton Illinois

    Re: Virgin Voyage - VTA ST-120 kit build

    Post by dalemurray on Sat Oct 06, 2018 4:31 pm

    Amazon failed me but Sam Ash music did not, I bought the required tube there.

    Variac is pumping out 119.8 volts.
    1n4007 Diodes are Dioding (yellow page mod)
    Bias on all four tubes are between .501-.503 volts.

    I've been hammering it with a couple typical test tracks:
    Yello - Planet Dada (Flamboyant Mix) <-- abusive bass, really interesting sound stage. Never heard this before attending Axpona this year. Used in several rooms.
    ZZ Top - Blue Jean Blues <-- Nice and tight. Guitar sounds like a dream.
    Fiona Apple - Sleep to dream <-- C'mon. The low rumble is wonderful.
    Lorde - Royals <-- Again, low rumble. Another favorite at Axpona.
    Lou Reed - Walk on the Wild Side <-- So many goof things to be said about this recording, sad I never listened to it on a decent system until this year. Never appreciated it.

    Other stuff sprinkled in here and there.

    This has been a great learning experience and no trips the emergency room or fire extinguishers. Now I must decide if I am going to build a preamp and phono preamp or buy something decent in the used market.

    Super happy now.
    And to think I was considering $2500 on a primaluna or rogue. In the end I will spend about the same but have a much better product.
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    dalemurray

    Posts : 26
    Join date : 2018-09-25
    Location : Wheaton Illinois

    Re: Virgin Voyage - VTA ST-120 kit build

    Post by dalemurray on Thu Oct 11, 2018 8:59 pm

    A few photos of it completed.




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    arledgsc

    Posts : 491
    Join date : 2012-11-30
    Location : SF Bay CA

    Re: Virgin Voyage - VTA ST-120 kit build

    Post by arledgsc on Fri Oct 12, 2018 1:15 pm

    My SS rectified ST-120 has the unused rectifier heater +5V winding connected as a "bucker" to reduce the effective line voltage about 4 to 5V.  Brings SS rectified HV down to +500Vdc when the line voltage is 120Vac.  Has worked great for years.

    See the diagram link below for wiring.  It is simply the unused heater winding connected in series with one side of the incoming AC.  I chose to wire Neutral instead of the AC Hot (Live) through the heater winding secondary.  Keeps the line voltage in the secondary near ground potential (+/-5Vac) versus +/-115V when using Hot.  Assuming of course the incoming AC circuit is wired correctly.  For additional safety also have a grounded earth chassis and use GFCI.

    Be sure to test HV AC after wiring to verify you get Buck instead of Boost.  Unplug the rectifier and measure HV AC before and after.  You should see a difference of about 20-25Vac either low or high versus the "before" measurement.  If higher reverse the secondary heater connections and measure again.  

    All the bucker wired transformer output voltages are reduced about 5% including the 6.3V heaters.  Never had any issues and I use 6SN7s types and KT120s with higher heater current draw.  And another "bucker" benefit is the amp runs a tiny bit cooler plus much cooler with straight SS rectifier like WZ1 with no sag resistors.  And TDR or some other method of holding off HV until the signal tubes have warmed sufficiently is a must.  I use 40 sec delay and never have any amplifier power start-up drama.  

    Transformer Bucker Wiring Diagram  Thanks corndog!

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    Re: Virgin Voyage - VTA ST-120 kit build

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