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    Auto-Bias board on Roy's website?

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    mazeeff

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    Auto-Bias board on Roy's website?

    Post by mazeeff on Tue Feb 27, 2018 2:36 pm

    I was browsing Roy's web site at;

    http://www.tubes4hifi.com/ST70.htm

    and came across a Auto-bias board for the ST70 and ST120. Have I missed something, or is this something new. I could not find any discussion on it!

    Mike
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    sKiZo

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    Re: Auto-Bias board on Roy's website?

    Post by sKiZo on Tue Feb 27, 2018 3:36 pm

    Did a nice job of hiding it halfway down the page, eh ... ;-}



    Looks like it'd be an easy install too ... just swap the leads from the existing pots on the VTA board and tap the power supply ...

    PS - maybe Roy can chime in and tell us why the change of heart?

    http://dynacotubeaudio.forumotion.com/t3341p25-auto-bias#30245
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    jfine

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    Re: Auto-Bias board on Roy's website?

    Post by jfine on Thu Mar 01, 2018 2:35 am

    Is something like this even possible for the M125?
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    corndog71

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    Re: Auto-Bias board on Roy's website?

    Post by corndog71 on Thu Mar 01, 2018 10:11 am

    jfine wrote:Is something like this even possible for the M125?

    Yes, but you need a board for each amp plus a few additional parts to make it work.

    I'm probably going to get one for my VTA120.
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    jfine

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    Re: Auto-Bias board on Roy's website?

    Post by jfine on Thu Mar 01, 2018 1:52 pm

    corndog71 wrote:
    Yes, but you need a board for each amp plus a few additional parts to make it work.

    I would need Bob Latino-type instructions as well, so I don't f!@$ it up.
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    deepee99

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    Re: Auto-Bias board on Roy's website?

    Post by deepee99 on Fri Mar 02, 2018 3:08 pm

    I have one in my Sachs-modified ST-120. Highly recommend. Glad Roy is now offering them as an option for kit-builders. ARC has been using auto-bias for years so it's not exactly a "new" technology, however these new boards are cutting-edge in quality and performance.
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    sKiZo

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    Re: Auto-Bias board on Roy's website?

    Post by sKiZo on Fri Mar 02, 2018 3:51 pm

    [quote="mazeeff"]
    erhard-audio wrote:I would be interested to see one of these mounted in a ST120. It looks like it would be a tight fit, and you would cover up those neat status LEDs!

    One advantage to a custom case ... I got acres of room to mount one if I wanted to.

    Thing is, I already got meters and easily accessible bias pots, so tuning the tubes on the fly is right easy.

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    deepee99

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    Re: Auto-Bias board on Roy's website?

    Post by deepee99 on Fri Mar 02, 2018 4:04 pm

    sKiZo wrote:
    mazeeff wrote:
    erhard-audio wrote:I would be interested to see one of these mounted in a ST120. It looks like it would be a tight fit, and you would cover up those neat status LEDs!

    One advantage to a custom case ... I got acres of room to mount one if I wanted to.

    Thing is, I already got meters and easily accessible bias pots, so tuning the tubes on the fly is right easy.


    True, and manual bias-tune gets you out of your listening chair once a month or so. OTOH, with auto-bias, I got a pretty good price for my Fluke. Razz
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    pavlikkkk

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    Re: Auto-Bias board on Roy's website?

    Post by pavlikkkk on Mon Mar 05, 2018 3:35 pm

    sKiZo wrote:Did a nice job of hiding it halfway down the page, eh ... ;-}



    Looks like it'd be an easy install too ... just swap the leads from the existing pots on the VTA board and tap the power supply ...

    PS - maybe Roy can chime in and tell us why the change of heart?

    http://dynacotubeaudio.forumotion.com/t3341p25-auto-bias#30245
    Hi,
    I can explain this module connection when he sends me the amplifier scheme
    Pavel
    audioamp.eu
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    jfine

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    Re: Auto-Bias board on Roy's website?

    Post by jfine on Mon Mar 05, 2018 11:38 pm

    pavlikkkk wrote:
    Hi,
    I can explain this module connection when he sends me the amplifier scheme
    Pavel
    audioamp.eu

    The M125 monoblock scheme?
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    tubes4hifi
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    Re: Auto-Bias board on Roy's website?

    Post by tubes4hifi on Tue Mar 06, 2018 12:50 pm

    I only check this forum maybe once a week, unlike Bob who runs it and is usually on here everyday.
    Yes, I've got it on my webpage, and no, as Bob points out, it's not going to be a simple install due to the fact that the mounting dimensions of it don't line up
    with any holes in the chassis, and I for one, find it near impossible to drill thru heavy guage stainless steel, but Don Sachs and I are using this module in our custom amp builds.
    NEVER a worry about bias, NEVER a worry about tube failure, so well worth it to me.
    Other than physically mounting and attaching it inside an ST70 or ST120, wiring it up is simple, you connect 6vac from the filament supply,
    connect the raw bias DC from the VTA board, eliminate all the cathode resistors and bias pots, as those are on the auto-bias board.
    Not a simple connection to M125s however, as you would need to add quite a few parts (extra coupling caps and grid resistors) and break all the connections
    between the paralleled tubes. I have an ST70 customer doing an install this week, and will get back here with a photo hopefully within a week.
    For anyone with their own custom chassis (non-stainless steel, hopefully regular steel, aluminum, or wood, install should be easy.
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    tubes4hifi
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    Re: Auto-Bias board on Roy's website?

    Post by tubes4hifi on Tue Mar 06, 2018 1:07 pm

    I've been in contact with Pavel for the correct install for the M125, you would need to add additional coupling caps and grid resistors,
    and break the existing connections between the paralled output tubes so that each would be completely independent.
    No problem, ARC and others have been doing this for years. As is, in an M125, if you have one tube in a pair go into runaway, you'll likely loose both tubes,
    and possibly the transformers. Won't happen with auto-bias. Don't ask, I know Bob doesn't want to do a total redesign of the M125s.
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    deepee99

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    Re: Auto-Bias board on Roy's website?

    Post by deepee99 on Tue Mar 06, 2018 1:14 pm

    tubes4hifi wrote:I've been in contact with Pavel for the correct install for the M125, you would need to add additional coupling caps and grid resistors,
    and break the existing connections between the paralled output tubes so that each would be completely independent.
    No problem, ARC and others have been doing this for years.   As is, in an M125, if you have one tube in a pair go into runaway, you'll likely loose both tubes,
    and possibly the transformers.   Won't happen with auto-bias.   Don't ask, I know Bob doesn't want to do a total redesign of the M125s.
    I have become quite a fan of that auto-bias board. It's tube-specific as to plate volts and bias, yet line fluctuations don't throw it off. Mine's set up for KT-88s. I do check bias from time-to-time, just to keep an eye on the board, but there's never been the slightest variation. I miss the fireworks of a red-plating or dying output tube but think I will survive without them.
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    sKiZo

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    Re: Auto-Bias board on Roy's website?

    Post by sKiZo on Tue Mar 06, 2018 2:16 pm

    Wonder if something like this would work? This was for a 24v power supply to power my aux lighting ...



    Simple aluminum bracket with posts that used the existing transformer screws. Not sure if there'd be enough clearance between the base plate and bottom of the transformer though. Once again, not a problem with my custom case.
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    Bob Latino
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    Re: Auto-Bias board on Roy's website?

    Post by Bob Latino on Tue Mar 06, 2018 2:28 pm

    Below is Pavel's autobias circuit as it should be attached in a VTA M-125 amp.

    Bob





    Last edited by Bob Latino on Sat Apr 28, 2018 6:22 pm; edited 3 times in total
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    jfine

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    Re: Auto-Bias board on Roy's website?

    Post by jfine on Tue Mar 06, 2018 2:50 pm

    tubes4hifi wrote:As is, in an M125, if you have one tube in a pair go into runaway, you'll likely loose both tubes, and possibly the transformers.

    Don't know about any other M125 owners, but dammit that bothers me.
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    Bob Latino
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    Re: Auto-Bias board on Roy's website?

    Post by Bob Latino on Tue Mar 06, 2018 4:39 pm

    jfine wrote:

    Don't know about any other M125 owners, but dammit that bothers me.

    I do not totally agree with what Roy has said .. In the 12 years of selling the VTA amp kits no one has ever lost an output transformer when an output or driver tube "bit the dust". What usually happens is that the tube will die and blow the fuse and possibly take out the 10 ohm resistor to chassis ground on pin #8 of that tube socket. An output transformer burning out ? It just never happens ...

    Bob
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    jfine

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    Re: Auto-Bias board on Roy's website?

    Post by jfine on Tue Mar 06, 2018 7:56 pm

    Bob Latino wrote:

    I do not totally agree with what Roy has said .. In the 12 years of selling the VTA amp kits no one has ever lost an output transformer when an output or driver tube "bit the dust". What usually happens is that the tube will die and blow the fuse and possibly take out the 10 ohm resistor to chassis ground on pin #8 of that tube socket. An output transformer burning out ? It just never happens ...

    Bob

    PHEW!

    Bob, do you think there's room inside the M125 for this board? Maybe stacked somehow over the other circuit board, possibly moving the existing caps out of the way?
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    tubes4hifi
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    Re: Auto-Bias board on Roy's website?

    Post by tubes4hifi on Tue Mar 06, 2018 8:21 pm

    for an M125, either directly under the four output tubes, or directly under the driver board (for which mounting might require an "adaptor")
    plus of course with an M125 you would need to add at least two additional output caps and two more resistors, plus remove alot of other existing stuff.
    If there was enough interest, I could design an adaptor board that included the extra parts and thorough instructions, as this is a mod you do NOT want to mess up!!
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    jfine

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    Re: Auto-Bias board on Roy's website?

    Post by jfine on Tue Mar 06, 2018 10:01 pm

    tubes4hifi wrote:for an M125, either directly under the four output tubes, or directly under the driver board (for which mounting might require an "adaptor")
    plus of course with an M125 you would need to add at least two additional output caps and two more resistors, plus remove alot of other existing stuff.
    If there was enough interest, I could design an adaptor board that included the extra parts and thorough instructions, as this is a mod you do NOT want to mess up!!

    YES! I'm in!
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    tubes4hifi
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    Re: Auto-Bias board on Roy's website?

    Post by tubes4hifi on Wed Mar 07, 2018 4:49 pm

    stand by, when I return from vacation in late April, I will have an adaptor board for the M125s, and a drop-in board for the ST70 & ST120 amps.
    Start the drooling now . . . . Very Happy

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    jfine

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    Re: Auto-Bias board on Roy's website?

    Post by jfine on Wed Mar 07, 2018 5:39 pm

    Man you don't mess around, really appreciate your effort.

    Your support for hifi gear (Roy M. & Bob L.) is second to none.
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    deepee99

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    Re: Auto-Bias board on Roy's website?

    Post by deepee99 on Wed Mar 07, 2018 5:43 pm

    jfine wrote:Man you don't mess around, really appreciate your effort.

    Your support for hifi gear (Roy M. & Bob L.) is second to none.
    Amen to that. And to think they could've been squandering all this effort on TAS ads Twisted Evil
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    Roy

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    Re: Auto-Bias board on Roy's website?

    Post by Roy on Thu Mar 08, 2018 5:52 am

    Very nice =] Would probably require mounting of the driver capacitors topside not underside I think though in order for this board to piggyback underneath in a vta70 or 120 ?
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    tubes4hifi
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    Re: Auto-Bias board on Roy's website?

    Post by tubes4hifi on Thu Mar 08, 2018 8:43 pm

    Roy in Europe
    C17 & C18 are too tall, I will supply shorter ones with the auto-bias board.
    3/4" spacers also, which are big enough to clear those big K40Y PIO caps on the driver board.
    Roy @ Tubes4HiFi

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