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    Auto-Bias board on Roy's website?

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    Kramer

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

    Post by Kramer on Sun Apr 15, 2018 2:15 pm

    Wow, came here looking for the name of the bias board to order one and find that one is being custom designed for our amps Smile really appreciate all the effort you guys put into these amps. I will be purchasing one as soon as they are available.
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    CletusB

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

    Post by CletusB on Mon Apr 16, 2018 8:42 am

    tubes4hifi wrote: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


    Wow! this IS a very exciting development. bounce
    Now the question that's going to keep me awake at night is: do I wanna upgrade to this or do I wanna stay "old-school" and bias the amp myself every couple weeks when I wipe her down?  .....damned if I do, damned if I don't!  What a Face
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    deepee99

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

    Post by deepee99 on Mon Apr 16, 2018 10:57 am

    CletusB,
    I would seriously consider the auto-bias upgrade. You can still at least manually test bias, at least on the boards Don Sachs provides, but basically it's "set it and forget it." The beauty of the concept is that when an output tube runs amok, it dies quietly without hurting anyone else.
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    aguaazul

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

    Post by aguaazul on Mon Apr 16, 2018 11:26 am

    Looks like Pavel over at audioamp.eu has some info posted on his site:

    Drop In AutoBias ST-70 Page
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    pavlikkkk

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

    Post by pavlikkkk on Mon Apr 16, 2018 12:20 pm

    aguaazul wrote:Looks like Pavel over at audioamp.eu has some info posted on his site:

    Drop In AutoBias ST-70 Page

    I sent these tubes4hifi modules, it available in a few weeks for the United States.  Very Happy


    Last edited by pavlikkkk on Tue Apr 17, 2018 9:19 am; edited 1 time in total
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    Dave_in_Va

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

    Post by Dave_in_Va on Mon Apr 16, 2018 1:57 pm

    I like to bias my VTA ST70 myownself. It makes look like I know at least something.
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    pavlikkkk

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

    Post by pavlikkkk on Mon Apr 16, 2018 2:20 pm

    deepee99 wrote:
    pavlikkkk wrote:
    aguaazul wrote:Looks like Pavel over at audioamp.eu has some info posted on his site:

    Drop In AutoBias ST-70 Page

    I sent these tube4hifi modules, it available in a few weeks for the United States.  Very Happy
    Pavel,
    Are these the same boards Don Sachs uses?

    they are boards with the same circuit.
    The dimensions of the boards are adapted for direct mounting into the ST70 and M125 amplifiers.
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    CletusB

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

    Post by CletusB on Mon Apr 16, 2018 2:29 pm

    Dave_in_Va wrote:I like to bias my VTA ST70 myownself. It makes look like I know at least something.
    Matter of preference I guess.  I've built and owned tube amps before and have not had an issue.  My preference as well is to keep the amp "Old-School" and to do the bias adjustment is no problem for me when I'm dusting off the system every other weekend.
    Nice modification nonetheless!
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    arledgsc

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

    Post by arledgsc on Mon Apr 16, 2018 4:48 pm

    After reading Pavel's web site I have question.

    Soft-start when also using a relay board.  Pavel states to connect HV to the board only if "the amplifier is equipped with a delayed  connection anode voltage and connection with a time of more than 80 seconds."   How does bias ramp up and relay board timeout work together at start up in an ST-120 with a about 40 sec. relay delay timeout?  It seems the default relay board 20 sec delay is the same timeout as the bias soft-start which is no conflict and would work fine.  But I need to hold off slightly longer.  

    Thank you!  Nice feature!  Hope you sell 1Ks of these boards.
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    deepee99

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    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

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    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

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    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

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    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

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    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

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    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

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    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

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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

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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

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    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

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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

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    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

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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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