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    10A or 20A Bucker Transformer for M125's?

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    LeGrace

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    10A or 20A Bucker Transformer for M125's?

    Post by LeGrace on Sun Feb 04, 2018 1:16 pm

    To move my mains (typ 122v) closer to the comfort zone a bucker seems like the most economical way to proceed. I see folks using 6A rated ones quite often, but then the M125's are packing more horsepower then most amps, so at first I was contemplating a 10A rated model. But do I really need to assemble one for each amp? To save on effort couldn't I simply go with a single 20A rated transformer, like a Hammond 266V6B?

    Any helpful advice appreciated.

    audiobill

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    Re: 10A or 20A Bucker Transformer for M125's?

    Post by audiobill on Sun Feb 04, 2018 1:19 pm

    6 amps is plenty for each, 10 amps is plenty for two.
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    Bob Latino
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    Re: 10A or 20A Bucker Transformer for M125's?

    Post by Bob Latino on Sun Feb 04, 2018 2:43 pm

    audiobill wrote:6 amps is plenty for each, 10 amps is plenty for two.

    Bill is correct here .. What I would do if it were my pair of M-125's running on 122+ AC line voltage would be to get the 20 amp variac at Circuit Specialists at the link below. They offer free shipping to the USA but Legrace is in Canada so the shipping would be extra. This model also has TWO AC outputs - one for each M-125.

    20 amp variac at Circuit Specialists in AZ

    They also sell a 5 amp model that would be fine for a single ST-70 or ST-120.

    5 amp rated variac

    Set your variac to give about 118 VAC output with whatever AC output is coming from your wall outlet.

    Bob

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    Dahlberg

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    Re: 10A or 20A Bucker Transformer for M125's?

    Post by Dahlberg on Sun Feb 04, 2018 5:56 pm

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    LeGrace

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    Re: 10A or 20A Bucker Transformer for M125's?

    Post by LeGrace on Mon Feb 05, 2018 11:18 am

    Thanks for all the help, not to mention saving me some $$!
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    gktamps

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    Re: 10A or 20A Bucker Transformer for M125's?

    Post by gktamps on Mon Feb 05, 2018 5:58 pm

    Although it sounds like you will be buying a Variac instead, just to add an observation to this discussion; I made a 8A bucking transformer for my pair of M-125s running KT120s, and it got pretty warm in operation. I replaced it with a 15A.

    BNR_1

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    Re: 10A or 20A Bucker Transformer for M125's?

    Post by BNR_1 on Tue Feb 06, 2018 12:39 am

    I know for vintage gear people drops their line voltage to around 115 to 117v. But for these modern made amps, I thought the PT was designed for 120 to 124 volts.
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    Captain Coconut

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    Re: 10A or 20A Bucker Transformer for M125's?

    Post by Captain Coconut on Tue Feb 06, 2018 11:51 am

    I use a 15 amp rated (bucker) transformer for the entire system. It’s a 5V CT filament tranny that I have wired to drop 2.5V and 5V. The power can be a little erratic around here; some days it’s 122,so I drop 5V, other days it’s 120, so I drop 2.5V. It’s controlled by a simple “ON-ON” toggle switch. A 3-way light switch will work too.
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    LeGrace

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    Re: 10A or 20A Bucker Transformer for M125's?

    Post by LeGrace on Tue Feb 06, 2018 4:43 pm

    I see a 16A rated Hammond that is only a few dollars more then the 10A.  Whereas the 20A units cost like double.
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    cci1492

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    Re: 10A or 20A Bucker Transformer for M125's?

    Post by cci1492 on Wed Feb 14, 2018 12:29 pm

    Bob Latino wrote:
    audiobill wrote:6 amps is plenty for each, 10 amps is plenty for two.

    Bill is correct here .. What I would do if it were my pair of M-125's running on 122+ AC line voltage would be to get the 20 amp variac at Circuit Specialists at the link below. They offer free shipping to the USA but Legrace is in Canada so the shipping would be extra. This model also has TWO AC outputs - one for each M-125.

    20 amp variac at Circuit Specialists in AZ

    They also sell a 5 amp model that would be fine for a single ST-70 or ST-120.

    5 amp rated variac

    Set your variac to give about 118 VAC output with whatever AC output is coming from your wall outlet.

    Bob


    Today only! I used PROMO CODE "VDAY" and got it for 15% OFF:

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    LeGrace

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    Re: 10A or 20A Bucker Transformer for M125's?

    Post by LeGrace on Thu Feb 15, 2018 2:50 pm

    So got the bucker put together, using a Hammond 167U6 transformer. 16A model that I suppose could be described as overkill, but difference cost wise from a 10A was so minor I figured what the heck.

    Voltage reading is now 117.8 versus 122v. I cant help but wonder if I had done this sooner would it have prevented some of my prior tube failures? Will never know, but I see it as good insurance for the future.
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    Bob Latino
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    Re: 10A or 20A Bucker Transformer for M125's?

    Post by Bob Latino on Thu Feb 15, 2018 3:08 pm

    On the back of the parts list on every VTA amp kit is a note to check your incoming AC line voltage. There is also the suggestion to use a variac if your normal incoming line voltage is 122 VAC or above.

    Bob
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    LeGrace

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    Re: 10A or 20A Bucker Transformer for M125's?

    Post by LeGrace on Thu Feb 15, 2018 5:47 pm

    When I built my M125's I had no clue about the importance of line voltage. I did not know I was falling into the red zone, just wondered why am I blowing tubes left and right. Lesson learned, no more living on the edge!

    buchela

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    Re: 10A or 20A Bucker Transformer for M125's?

    Post by buchela on Thu Feb 15, 2018 6:24 pm

    What are the possible consequences to run M-125 monoblocks on 122V ?.
    What is the ideal voltage for these amps ?


    Last edited by buchela on Thu Feb 15, 2018 6:26 pm; edited 1 time in total (Reason for editing : added second paragraph)

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