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    Auto-Bias board on Roy's website?

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    pavlikkkk

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

    Post by pavlikkkk on Fri Jun 08, 2018 6:50 am

    pichacker wrote:If pin 8 is the cathode and pin 1 unused then the MOV should go the other side of the fuse. Ie pin 1 to ground.

    [Pin 8 Cathode] -- [FUSE] -- [Pin 6] -- [Bias Board and MOV to ground]

    That way the MOV clamps the input to the bias board and the fuse then fails.

    Yes. The MOV V8ZA1P reliably switches to 15V overvoltage. Tested.
    Pavel



    New2Tubez

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

    Post by New2Tubez on Wed Jun 13, 2018 2:53 pm

    pavlikkkk wrote:
    jfine wrote:Question, (M125's)

    When auto bias board is installed, is it still possible to check the bias thru the existing front holes, or are these disconnected, or is there some relatively easy method to check to make sure bias stays consistent?

    I'm remake the AB-Q module (LEDs)...
    I have invent how to mount LEDs to the amp panel.
    I removed the SMD LED from the board.
    Into the LEDs pad I drill the holes in 0.8mm.
    I can use the LED with cable to go where I need it..



    So, has anyone relocated the LEDs? My board came from the second batch (I believe) and there's no LED mod here. I will do the install in the next week or so and was hoping to hear any experiences with this.

    If not, should I assume an unlit tube would lead to an unlit LED? Shouldn't it be the other way around? I'm very new to this and want to do it right.

    Roy has pretty much clarified everything else for me at this point.

    Thanks for all the helpful info on this forum. My amp sounds great so, I need reassurances before I mess up a good thing.
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    pavlikkkk

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

    Post by pavlikkkk on Wed Jun 13, 2018 3:50 pm

    New2Tubez wrote:
    pavlikkkk wrote:
    jfine wrote:Question, (M125's)

    When auto bias board is installed, is it still possible to check the bias thru the existing front holes, or are these disconnected, or is there some relatively easy method to check to make sure bias stays consistent?

    I'm remake the AB-Q module (LEDs)...
    I have invent how to mount LEDs to the amp panel.
    I removed the SMD LED from the board.
    Into the LEDs pad I drill the holes in 0.8mm.
    I can use the LED with cable to go where I need it..




    So, has anyone relocated the LEDs? My board came from the second batch (I believe) and there's no LED mod here. I will do the install in the next week or so and was hoping to hear any experiences with this.

    If not, should I assume an unlit tube would lead to an unlit LED? Shouldn't it be the other way around? I'm very new to this and want to do it right.

    Roy has pretty much clarified everything else for me at this point.

    Thanks for all the helpful info on this forum. My amp sounds great so, I need reassurances before I mess up a good thing.

    Openings for external LED  have newer boards (www.audioamp.eu on board).
    On the elderly boards you would have to drill holes according to the instructions.
    Pavel


    Last edited by pavlikkkk on Sat Jun 16, 2018 3:30 pm; edited 1 time in total
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    pichacker

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

    Post by pichacker on Thu Jun 14, 2018 8:11 am

    Pavel,

    Since the LED is the reference for the constant current source and we know different colour LEDs have different voltage drops will this be an issue?

    Steve
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    pavlikkkk

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

    Post by pavlikkkk on Thu Jun 14, 2018 12:08 pm

    pichacker wrote:Pavel,

    Since the LED is the reference for the constant current source and we know different colour LEDs have different voltage drops will this be an issue?

    Steve

    The LED can be any color and luminosity. It does not matter. In this connection works as a source of constant current. I Tested !
    Pavel

    New2Tubez

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

    Post by New2Tubez on Fri Jun 15, 2018 10:05 pm

    pavlikkkk wrote:
    New2Tubez wrote:
    pavlikkkk wrote:
    jfine wrote:Question, (M125's)

    When auto bias board is installed, is it still possible to check the bias thru the existing front holes, or are these disconnected, or is there some relatively easy method to check to make sure bias stays consistent?

    I'm remake the AB-Q module (LEDs)...
    I have invent how to mount LEDs to the amp panel.
    I removed the SMD LED from the board.
    Into the LEDs pad I drill the holes in 0.8mm.
    I can use the LED with cable to go where I need it..



    So, has anyone relocated the LEDs? My board came from the second batch (I believe) and there's no LED mod here. I will do the install in the next week or so and was hoping to hear any experiences with this.

    If not, should I assume an unlit tube would lead to an unlit LED? Shouldn't it be the other way around? I'm very new to this and want to do it right.

    Roy has pretty much clarified everything else for me at this point.

    Thanks for all the helpful info on this forum. My amp sounds great so, I need reassurances before I mess up a good thing.

    Openings for external LED  have newer boards (www.audioamp.eu on board).
    On the elderly boards you would have to drill holes according to the instructions.
    Pavel

    Thanks for letting me know. I'll have a look for the drilled holes and the audio amp.eu on it.

    New2Tubez

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

    Post by New2Tubez on Fri Jun 15, 2018 10:07 pm

    pavlikkkk wrote:
    pichacker wrote:Pavel,

    Since the LED is the reference for the constant current source and we know different colour LEDs have different voltage drops will this be an issue?

    Steve

    The LED can be any color and luminosity. It does not matter. In this connection works as a source of constant current. I Tested !
    Pavel

    Does this apply to the bi-color LED as well? If not can you specify please?
    Thanks,
    Ned
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    aguaazul

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

    Post by aguaazul on Sat Jun 16, 2018 1:55 pm

    pavlikkkk wrote:
    pichacker wrote:If pin 8 is the cathode and pin 1 unused then the MOV should go the other side of the fuse. Ie pin 1 to ground.

    [Pin 8 Cathode] -- [FUSE] -- [Pin 6] -- [Bias Board and MOV to ground]

    That way the MOV clamps the input to the bias board and the fuse then fails.

    Yes. The MOV V8ZA1P reliably switches to 15V overvoltage. Tested.
    Pavel




    So what is the advantage of setting it up with the MOV vs just a fuse across pins 1 & 8?
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    Kramer

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

    Post by Kramer on Sat Jun 16, 2018 2:09 pm

    aguaazul wrote:
    pavlikkkk wrote:
    pichacker wrote:If pin 8 is the cathode and pin 1 unused then the MOV should go the other side of the fuse. Ie pin 1 to ground.

    [Pin 8 Cathode] -- [FUSE] -- [Pin 6] -- [Bias Board and MOV to ground]

    That way the MOV clamps the input to the bias board and the fuse then fails.

    Yes. The MOV V8ZA1P reliably switches to 15V overvoltage. Tested.
    Pavel




    So what is the advantage of setting it up with the MOV vs just a fuse across pins 1 & 8?

    It's my understanding that with just the fuse a output tube short could still travel back to the AB board and cause damage. The varistor will sit there doing nothing until the voltage increases during a tube short where it will open up and the high voltage will be directed through to ground instead of the AB board preventing damage.
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    pavlikkkk

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

    Post by pavlikkkk on Sat Jun 16, 2018 2:51 pm

    Kramer wrote:
    aguaazul wrote:
    pavlikkkk wrote:
    pichacker wrote:If pin 8 is the cathode and pin 1 unused then the MOV should go the other side of the fuse. Ie pin 1 to ground.

    [Pin 8 Cathode] -- [FUSE] -- [Pin 6] -- [Bias Board and MOV to ground]

    That way the MOV clamps the input to the bias board and the fuse then fails.

    Yes. The MOV V8ZA1P reliably switches to 15V overvoltage. Tested.
    Pavel
    So what is the advantage of setting it up with the MOV vs just a fuse across pins 1 & 8?

    It's my understanding that with just the fuse a output tube short could still travel back to the AB board and cause damage. The varistor will sit there doing nothing until the voltage increases during a tube short where it will open up and the high voltage will be directed through to ground instead of the AB board preventing damage.

    Yes, the varistor normally does nothing at all.
    avatar
    aguaazul

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

    Post by aguaazul on Sat Jun 16, 2018 7:40 pm

    pavlikkkk wrote:
    Kramer wrote:
    aguaazul wrote:
    pavlikkkk wrote:
    pichacker wrote:If pin 8 is the cathode and pin 1 unused then the MOV should go the other side of the fuse. Ie pin 1 to ground.

    [Pin 8 Cathode] -- [FUSE] -- [Pin 6] -- [Bias Board and MOV to ground]

    That way the MOV clamps the input to the bias board and the fuse then fails.

    Yes. The MOV V8ZA1P reliably switches to 15V overvoltage. Tested.
    Pavel
    So what is the advantage of setting it up with the MOV vs just a fuse across pins 1 & 8?

    It's my understanding that with just the fuse a output tube short could still travel back to the AB board and cause damage. The varistor will sit there doing nothing until the voltage increases during a tube short where it will open up and the high voltage will be directed through to ground instead of the AB board preventing damage.

    Yes, the varistor normally does nothing at all.

    Why the move from pin 1 to pin 6?
    Would the MOV from pin 1 to ground work also?
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    tubes4hifi
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    Re: Auto-Bias board on Roy's website?

    Post by tubes4hifi on Sat Jun 16, 2018 8:08 pm

    Pavel just used pin 6 as a convenient tie point, but personally I don't like that because then you lose the tie point for the 1K grid resistor,
    I rather just add a terminal strip in there somewhere if you want to add the MOVs.
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    pavlikkkk

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

    Post by pavlikkkk on Sun Jun 17, 2018 1:53 am

    aguaazul wrote:
    pavlikkkk wrote:
    Kramer wrote:
    aguaazul wrote:
    pavlikkkk wrote:
    pichacker wrote:If pin 8 is the cathode and pin 1 unused then the MOV should go the other side of the fuse. Ie pin 1 to ground.

    [Pin 8 Cathode] -- [FUSE] -- [Pin 6] -- [Bias Board and MOV to ground]

    That way the MOV clamps the input to the bias board and the fuse then fails.

    Yes. The MOV V8ZA1P reliably switches to 15V overvoltage. Tested.
    Pavel
    So what is the advantage of setting it up with the MOV vs just a fuse across pins 1 & 8?

    It's my understanding that with just the fuse a output tube short could still travel back to the AB board and cause damage. The varistor will sit there doing nothing until the voltage increases during a tube short where it will open up and the high voltage will be directed through to ground instead of the AB board preventing damage.

    Yes, the varistor normally does nothing at all.

    Why the move from pin 1 to pin 6?
    Would the MOV from pin 1 to ground work also?
    the fuse between pin 1 (G3) and 8 (Cath) makes no sense. Cath is connected to G3 (1 + 8 ) and it is all protected by a fuse and a varistor. Pin 6 is the connection point.
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    tubes4hifi
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    Re: Auto-Bias board on Roy's website?

    Post by tubes4hifi on Tue Jun 19, 2018 12:31 pm

    There are many ways to make an electrical connection that has the same results.  I don't disagree with the electrical connection that Pavel has suggested, I just don't prefer using pin 6 of the tube,
    I'd rather keep the grid resisitor where it is.   And just as a fuse in not a necessity, the MOV is not a necessity, but each has it's place in making a better solution. (the AB is not a necessity either).
    So below is a diagram of how I would personally connect things.  It could be done without the terminal strip, but is easier for most to just add one terminal strip between each pair of output tubes.
    Left channel on one side of the amp, Right channel on the other side of the amp.   Just my personal preference.  Not right or wrong.
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    pichacker

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

    Post by pichacker on Wed Jun 20, 2018 2:39 am

    Like in the picture of my post 171.... Smile
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    Kramer

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

    Post by Kramer on Thu Jun 21, 2018 9:04 pm

    Here is how I am planning on wiring them up in case this helps.

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    pavlikkkk

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

    Post by pavlikkkk on Fri Jun 22, 2018 12:30 am

    Kramer wrote:Here is how I am planning on wiring them up in case this helps.

    Yes, this connection reliably protects AB-Q against short circuit in an tube.
    Pavel
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    Kramer

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

    Post by Kramer on Fri Jun 22, 2018 1:39 pm

    Wired the fuses and varisters in using the configuration shown above. Tested to be sure everything was correct and installed the tubes. Fired the amp up and everything is working properly.

    ericoto

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

    Post by ericoto on Fri Jun 22, 2018 2:38 pm

    Just received my auto bias boards for pair of M125's, does anyone have any photos of it installed in an M125, IS the notch on the board to accommodate c16 and c17 on driver board? What do I do with the PIO capacitors on the driver board?

    Thanks
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    Kramer

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

    Post by Kramer on Fri Jun 22, 2018 6:43 pm

    ericoto wrote:Just received my auto bias boards for pair of M125's, does anyone have any photos of it installed in an M125, IS the notch on the board to accommodate c16 and c17 on driver board? What do I do with the PIO capacitors on the driver board?

    Thanks

    Bob posted a photo earlier in the thread that shows one installed in a M125, it's a bit close up but it may help with the orientation. The installation into the VTA120 required replacing two capacitors to shorter caps of the same value to properly fit over the driver board. The standoff screws should pull the board away enough for the POI caps to fit ok but results may vary, I used a strip of thick electrical tape on the side of the POI caps facing the A/B board just in case.
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    aguaazul

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

    Post by aguaazul on Sun Jul 15, 2018 5:54 pm

    pavlikkkk wrote:
    Kramer wrote:Here is how I am planning on wiring them up in case this helps.

    Yes, this connection reliably protects AB-Q against short circuit in an tube.
    Pavel


    I did a variation on this theme:



    I like the idea of the fuse holders on a single terminal strip. These are the old rat shack terminal strips. The tabs are a little tight for the fuse holders, so I did a little delicate file work to put a tiny notch in the insides of the tabs.


    tomlang

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

    Post by tomlang on Thu Aug 16, 2018 8:57 am

    This seems like a great development.  I appreciate the effort the designer (Pavel) goes in engaging the community with this.  Some questions:

    1. Are the tubesforhifi st70 board and the AB-Q board the same except for the footprint of the pcb?
    2. Is there any effort to put protection components for the output tubes i.e. varistors, etc. on the board itself?
    3. Finally is this is a fully assembled board?
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    pavlikkkk

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

    Post by pavlikkkk on Thu Aug 16, 2018 12:43 pm

    tomlang wrote:This seems like a great development.  I appreciate the effort the designer (Pavel) goes in engaging the community with this.  Some questions:

    1. Are the tubesforhifi st70 board and the AB-Q board the same except for the footprint of the pcb?
    2. Is there any effort to put protection components for the output tubes i.e. varistors, etc. on the board itself?
    3. Finally is this is a fully assembled board?

    Answers to questions:
    1)The AB-Q PCB is electrically the same as the PCB AB-Q-ST70-ST120.
    2)Varistor should not be on PCB, nor fuse. In case of a short circuit, there is a high voltage on these components and a the short can damage the PCB.
    3)The boards are fitted with all the components except varistors and fuses.
    Pavel
    audioamp.eu

    tomlang

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

    Post by tomlang on Fri Aug 31, 2018 9:22 am

    Roy, you mention earlier "connect bias voltage from C17 (+ and - leads) as per drawing".  You also mention replacing C17 and C18 with shorter caps.  If I'm reading the schematic correctly, C17 is the first capacitor connected to the half wave rectifier diode.  Therefore, C18 as well as R39 (between C17 and C18) could be removed??

    I found the correction: "update 5-18 change bias connection to C17 instead of C18"

    Pavel, how clean does the bias supply need to be? Is just one filter capacitor sufficient or is a two stage filter required?
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    tubes4hifi
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    Re: Auto-Bias board on Roy's website?

    Post by tubes4hifi on Fri Aug 31, 2018 1:25 pm

    the auto-bias connection to bias from the driver board is to C17, so yes, it's possible to remove C18 and R39, but not necessary

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