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    Auto-Bias board on Roy's website?

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    deepee99

    Posts : 1911
    Join date : 2012-05-23
    Location : Wallace, Idaho

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

    Post by deepee99 on Mon Apr 16, 2018 4:57 pm

    It's not bias on the grids that ramps up. It's plate voltage in a very smooth curve. You can fire up the pre-amp(s) at the same time you fire up the main(s). By the time the preamp has done its spitting and pharting, the outputs will light up. It really is a very cool design.
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    arledgsc

    Posts : 483
    Join date : 2012-11-30
    Location : SF Bay CA

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

    Post by arledgsc on Mon Apr 16, 2018 5:22 pm

    oh!...Oh! So "two mints in one". Soft HV start plus auto-bias. Neato! My tubes would appreciate a softer ramp of HV.

    I guess no relay board needed. And, if so, can I adjust the soft HV ramp for more delay to start (40 seconds)?

    But with no relay board what about power failures/ brownout protection? Maybe Roy has that covered with large forward biased diodes on the new board's HV voltage outputs.
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    deepee99

    Posts : 1911
    Join date : 2012-05-23
    Location : Wallace, Idaho

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

    Post by deepee99 on Mon Apr 16, 2018 6:23 pm

    arledgsc wrote:oh!...Oh!  So "two mints in one".  Soft HV start plus auto-bias.  Neato!  My tubes would appreciate a softer ramp of HV.

    I guess no relay board needed.  And, if so, can I adjust the soft HV ramp for more delay to start (40 seconds)?

    But with no relay board what about power failures/ brownout protection?  Maybe Roy has that covered with large forward biased diodes on the new board's HV voltage outputs.  
    Just buy a $30 *manual reset* GFCI off Amazon to protect your stuff from power failures and brownouts, and worries are over.
    Pavel's boards don't go full-tilt until about two minutes into the show. They are works of art.


    jwb474

    Posts : 9
    Join date : 2014-07-13

    Old Original ST70 with auto-bias

    Post by jwb474 on Mon Apr 16, 2018 11:10 pm

    Here are a couple of pictures showing how I mounted the original pwb. One thing that caught me off guard is since this is a old unit designed for the old 115VAC and since I have solid state rectifiers and the way the auto bias soft starts there is a period in which the B+ exceeded the rating of my new quad cap from Dynakits. The voltage went to 550VDC and took out my cap. I have since replaced it with the higher rated quad cap. The reason is the auto-bias allows 0 plate current for a while and this will allow the quad cap to charge to 1.414 x peak ac voltage even with a tube rectifier since no current draw allows for very little drop. I finally got around to mapping out the circuit and I see no easy way to modify it to prevent this condition.



       " />

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    pavlikkkk

    Posts : 14
    Join date : 2018-03-02
    Age : 71
    Location : Czech Republic

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

    Post by pavlikkkk on Tue Apr 17, 2018 2:28 am

    arledgsc wrote:oh!...Oh!  So "two mints in one".  Soft HV start plus auto-bias.  Neato!  My tubes would appreciate a softer ramp of HV.

    I guess no relay board needed.  And, if so, can I adjust the soft HV ramp for more delay to start (40 seconds)?

    But with no relay board what about power failures/ brownout protection?  Maybe Roy has that covered with large forward biased diodes on the new board's HV voltage outputs.  
    Start time module lengthening is possible by increasing capacitor capacitance C12 to 47uF. Time is extended twice.
    In the event of a power failure, the module starts from the beginning.

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    deepee99

    Posts : 1911
    Join date : 2012-05-23
    Location : Wallace, Idaho

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

    Post by deepee99 on Tue Apr 17, 2018 6:30 am

    Pavel, I don't know if this matters, or applies to Roy's construct, but in Don Sachs' application of your board, the plate voltage actually drops and the bias is increased accordingly, to about .68/tube. In the end, you lose a little power on the output side of things, so somebody with a pair of Maggies and a VTA ST-120 might consider doubling down to a pair of M-125s, but if your speaks are around 90 dB efficient, you won't notice any difference and your output tubes will love you for it.
    I must say again the bias has held rock-steady at .68/tube with this board.
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    pavlikkkk

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

    Post by pavlikkkk on Wed Apr 18, 2018 12:33 pm

    deepee99 wrote:Pavel, I don't know if this matters, or applies to Roy's construct, but in Don Sachs' application of your board, the plate voltage actually drops and the bias is increased accordingly, to about .68/tube. In the end, you lose a little power on the output side of things, so somebody with a pair of Maggies and a VTA ST-120 might consider doubling down to a pair of M-125s, but if your speaks are around 90 dB efficient, you won't notice any difference and your output tubes will love you for it.
    I must say again the bias has held rock-steady at .68/tube with this board.
    I agree. For the MT-125S Icath 55-68mA / tube should be used.
    It is important to set Icath without modulation!
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    pavlikkkk

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

    Post by pavlikkkk on Wed Apr 18, 2018 2:35 pm

    arledgsc wrote:oh!...Oh!  So "two mints in one".  Soft HV start plus auto-bias.  Neato!  My tubes would appreciate a softer ramp of HV.

    I guess no relay board needed.  And, if so, can I adjust the soft HV ramp for more delay to start (40 seconds)?

    But with no relay board what about power failures/ brownout protection?  Maybe Roy has that covered with large forward biased diodes on the new board's HV voltage outputs.  
    Soft-start board is not required. When the amplifier is on, the grids on the pins GRID are maximally biased (-Umax bias supply). When the red LED goes out, the tubes begin to slowly open.
    The boards will be sold by you (SF) tubes4hifi.
    Pavel
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    pichacker

    Posts : 40
    Join date : 2016-08-01
    Age : 53
    Location : Near to London - UK

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

    Post by pichacker on Fri Apr 20, 2018 5:18 am

    What's the most cost effective way of getting one of these boards in the UK please?
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    pavlikkkk

    Posts : 14
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    Re: Auto-Bias board on Roy's website?

    Post by pavlikkkk on Fri Apr 20, 2018 6:45 am

    pichacker wrote:What's the most cost effective way of getting one of these boards in the UK please?

    In Europe sells boards auto-bias for amp. ST70 and M125 www.audioamp.eu
    Pavel
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    pichacker

    Posts : 40
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    Re: Auto-Bias board on Roy's website?

    Post by pichacker on Fri Apr 20, 2018 7:22 am

    Pavel,

    I have tried that site I can select the item and it goes into my basket. But when I try to check out there are no payment options offered so I cannot complete. I have tried with Google Chrome as well as IE.

    Steve
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    pavlikkkk

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

    Post by pavlikkkk on Fri Apr 20, 2018 7:29 am

    pichacker wrote:Pavel,

    I have tried that site I can select the item and it goes into my basket. But when I try to check out there are no payment options offered so I cannot complete. I have tried with Google Chrome as well as IE.

    Steve
    which module do you need?
    Pavel
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    pichacker

    Posts : 40
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    Age : 53
    Location : Near to London - UK

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

    Post by pichacker on Fri Apr 20, 2018 8:03 am

    Pavel,

    I was looking to try one out on my ST120. As per my avatar pic.

    Steve
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    pavlikkkk

    Posts : 14
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    Age : 71
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    Re: Auto-Bias board on Roy's website?

    Post by pavlikkkk on Fri Apr 20, 2018 8:42 am

    pichacker wrote:Pavel,

    I was looking to try one out on my ST120. As per my avatar pic.

    Steve
    In the eshop there was a modification - the addition of all the world states.
    Already works now.
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    pichacker

    Posts : 40
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    Location : Near to London - UK

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

    Post by pichacker on Fri Apr 20, 2018 9:05 am

    I can get further now but it stops at "specify the phone number" now Sad
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    pavlikkkk

    Posts : 14
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    Re: Auto-Bias board on Roy's website?

    Post by pavlikkkk on Fri Apr 20, 2018 9:47 am

    pichacker wrote:I can get further now but it stops at "specify the phone number" now Sad
    please write to pavel@manualy.cz
    Thanks
    Pavel
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    deepee99

    Posts : 1911
    Join date : 2012-05-23
    Location : Wallace, Idaho

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

    Post by deepee99 on Fri Apr 20, 2018 5:11 pm

    To cut back to the chase: Pavel's boards work. No way I'd go back.
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    tubes4hifi
    Admin

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    Join date : 2008-11-30

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

    Post by tubes4hifi on Sat Apr 21, 2018 2:23 pm

    I'm now back from vacation.   Haven't had a chance to update my website, but I have IN STOCK ten sets of ST70 auto-bias boards ($100 with shipping in USA),
    and five sets of M125 auto-bias boards ($150 a pair in USA with shipping).   Email me direct and I'll send you an invoice for payment.
    roymottram@yahoo.com
    www.tubes4hifi.com



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    CletusB

    Posts : 154
    Join date : 2018-02-11
    Age : 63
    Location : Trinidad & Tobago

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

    Post by CletusB on Sat Apr 21, 2018 2:30 pm

    can you email me the (ST-120) install manual?    ....I am considering it.

    buchela

    Posts : 45
    Join date : 2011-03-09

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

    Post by buchela on Sat Apr 21, 2018 7:26 pm

    Ditto here, I would like to see the installation manual first.
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    tubes4hifi
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    Re: Auto-Bias board on Roy's website?

    Post by tubes4hifi on Sat Apr 21, 2018 8:21 pm

    send me an email for a manual
    roymottram@yahoo.com
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    Bob Latino
    Admin

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

    Post by Bob Latino on Sun Apr 22, 2018 9:53 am

    Tubes4hifi AutoBias board shown below how it will install into a VTA ST-70/ST-120 amp.

    Bob


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    CletusB

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

    Post by CletusB on Sun Apr 22, 2018 9:59 am

    Hmmmmm   ....very tempting indeed study
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    aguaazul

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

    Post by aguaazul on Sun Apr 22, 2018 11:32 am

    How does that fit with the Russian PIO Caps? Is there room?
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    CletusB

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

    Post by CletusB on Sun Apr 22, 2018 11:37 am

    aguaazul wrote:How does that fit with the Russian PIO Caps? Is there room?
    I think it's gonna be very close, at least mine will. Laughing

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