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    Auto-Bias board on Roy's website?

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    jfine

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

    Post by jfine on Mon May 07, 2018 2:16 am

    Roy/Pavel,

    What happens with the M125 when a tube begins to fail, I understand the other 3 tubes would still run with correct bias, but is there some audible difference, like maybe less volume, etc., that would alert you that the tube failed? It would seem you could run with 3 tubes and maybe not notice?
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    pavlikkkk

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

    Post by pavlikkkk on Mon May 07, 2018 2:56 am

    jfine wrote:Roy/Pavel,

    What happens with the M125 when a tube begins to fail, I understand the other 3 tubes would still run with correct bias,  but is there some audible difference, like maybe less volume, etc., that would alert you that the tube failed? It would seem you could run with 3 tubes and maybe not notice?
    you will notice, of course... distortion will be significant, it can be heard Mad
    Pavel

    mazeeff

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

    Post by mazeeff on Mon May 07, 2018 4:15 am

    I recall a thread on another forum, where folks were talking about the benefits of maintaining consistent bias in a push-pull tube amp. They referred to a term called "Crossover distortion". This distortion was minimized by maintaining the same exact bias on each of the two tubes. Can someone explain how this level of distortion relates to overall THD? I think I also read that if the bias was equalized, that the amp would run in Class A mode for a greater part of the push-pull cycle. I have never quite understood this, but it would appear that the auto-bias board benefits both distortion, and class AB performance. Are these assumptions correct? Is the benefit audible??? For you Math Majors out there, if my bias difference were to be 10% in a push-pull amp, what would the distortion % be? A couple of days ago, I decided to put 4 meters on the bias points in my ST120 to watch the bias drift during warmup. It was surprising the amount of voltage drift that I saw during the 1st hour of warmup (without auto-bias). I saw 1 of my KT120's start at 60ma and work its way down to 55ma, and another that started at 50ma, and worked its way up to 55ma. The auto-bias board would eliminate this difference, without the need to warm up the amp. At this point, I don't see much downside to using auto-bias. The benefits appear to be significant!
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    Kramer

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

    Post by Kramer on Mon May 07, 2018 12:04 pm

    I just got the bias board installed in my st120 amp. I normally am very cautious of my bias levels after losing a tube shortly after assembling the kit. I would check pretty much every time I started the amp.

    After installing and doing a listening test I would say there is definitely a noted difference in the sound. Exactly what I would expect to hear from all tubes consistently at optimal bias levels. I am very happy with the results of installing this board and highly recommend it to anyone considering it. Thanks everyone involved for a great addon to our already amazing amps.


    Last edited by Kramer on Mon May 07, 2018 6:09 pm; edited 1 time in total
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    jfine

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

    Post by jfine on Mon May 07, 2018 6:04 pm

    deepee99 wrote:
    Plate volts go down, bias comes up to compensate. At least my SWAG. Need to ask one of the rocket scientists on the VTA Forum.

    Hmm, that's interesting. So you're saying that in order for the tube to perform, or sound like, like it did without the AB board, where it was maybe .5 bias, now you raise the bias in order for it to perform as before.

    Or I'm not reading it right.
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    jfine

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

    Post by jfine on Tue May 08, 2018 11:06 am

    I'll ask another way.

    1) What is the plate voltage of an M125 in stock form?

    2) What is the plate voltage of an M125 with the auto bias board installed?
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    pavlikkkk

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

    Post by pavlikkkk on Tue May 08, 2018 11:27 am

    jfine wrote:I'll ask another way.

    1) What is the plate voltage of an M125 in stock form?

    2) What is the plate voltage of an M125 with the auto bias board installed?

    I do not understand..
    Are you talking about the B + (anode voltage) in the amplifier, or what is the set AB-Q cathode current?
    Pavel
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    jfine

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

    Post by jfine on Tue May 08, 2018 11:31 am

    I'm talking about Post #130. That's what I am trying to understand as well.
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    aguaazul

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

    Post by aguaazul on Wed May 09, 2018 1:56 pm

    Deepee, do you know your plate voltage? Is it in the 450 Volt Range?
    I'm dropping in the octal board and the auto bias at the same time.
    Looking to set the per tube wattage a little over 31.
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    tubes4hifi
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    Re: Auto-Bias board on Roy's website?

    Post by tubes4hifi on Wed May 09, 2018 2:49 pm

    for M125 installs, go back to page 4 post #81 for an updated install diagram/instructions.
    The links connecting V1-V3 cathodes and V2-V4 cathodes need to be removed.
    Very sorry I overlooked this connection.
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    tubes4hifi
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    Re: Auto-Bias board on Roy's website?

    Post by tubes4hifi on Wed May 09, 2018 3:58 pm

    in support of the "fuse" addition discussion, anyone who has purchased auto-bias boards from me in the past two months,
    I am offering FREE fuses, email me For anyone else interested in fusing their tube amp output tubes, email me, $1 per fuse,
    these are mini-fuses about 8mm diameter and connect directly between pin 1 and pin 8 on each output tube.
    info@tubes4hifi.com
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    jfine

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

    Post by jfine on Wed May 09, 2018 7:03 pm

    Just checking, will the AB board automatically adjust for 2 tube option in M125, or does bias need reset?

    mazeeff

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

    Post by mazeeff on Thu May 10, 2018 3:58 am

    Pavel. What is the overall precision of the AB unit? If I set at 50ma, all tubes are set within what %? Once set, how much "difference" must exist, before the AB unit goes into adjustment mode?
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    jfine

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

    Post by jfine on Thu May 10, 2018 9:16 pm

    Pavel again..

    The M125 has the option of only running 2 tubes instead of 4. Will the board function properly when 2 tubes are removed like this?

    Actually, will the amp function properly?
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    pavlikkkk

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

    Post by pavlikkkk on Sat May 12, 2018 2:50 am

    mazeeff wrote:Pavel. What is the overall precision of the AB unit? If I set at 50ma, all tubes are set within what %? Once set, how much "difference" must exist, before the AB unit goes into adjustment mode?
    Accuracy is due to tolerance of cathode resistors. On AB-Q is 1% resistors.
    If you leave only two tubes in the amplifier, AB-Q will drive the other two.

    mazeeff

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

    Post by mazeeff on Thu May 17, 2018 7:14 am

    jfine wrote:Pavel again..

    The M125 has the option of only running 2 tubes instead of 4. Will the board function properly when 2 tubes are removed like this?

    Actually, will the amp function properly?

    Jeff. I just noticed that you have your M125's up for sale. You state in the sale, that the AB board has resulted in your selling them as "parts". Can you explain what happened?
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    CletusB

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

    Post by CletusB on Thu May 17, 2018 7:42 am

    Well, I'm thinking about installing the Auto-Bias board in my ST-120 amp (although I just hate fixin things that ain't broke).
    Would be great to see some more pics from people who did do the install.
    If I do it, the TDR board, when removed, will be installed in my Fender Twin-Reverb amp.
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    pavlikkkk

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

    Post by pavlikkkk on Thu May 17, 2018 8:27 am

    jfine wrote:Pavel again..

    The M125 has the option of only running 2 tubes instead of 4. Will the board function properly when 2 tubes are removed like this?

    Actually, will the amp function properly?
    When using only two end tubes, the primary OT impedance will not be properly adjusted.
    Pavel
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    deepee99

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

    Post by deepee99 on Thu May 17, 2018 3:53 pm

    CletusB wrote:Well, I'm thinking about installing the Auto-Bias board in my ST-120 amp (although I just hate fixin things that ain't broke).
    Would be great to see some more pics from people who did do the install.
    If I do it, the TDR board, when removed, will be installed in my Fender Twin-Reverb amp.
    It fits in my Sachs Kootenay, which is built on the ST-120 platform.
    Pavel's board is so gentle on the tubes I'd just stuff all four holes and not worry about tube life.
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    tubes4hifi
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    Re: Auto-Bias board on Roy's website?

    Post by tubes4hifi on Fri May 18, 2018 6:43 pm

    any M125 users who have installed the auto-bias and have it working correctly?
    If yes, let's hear about it, if not, email me or PM

    gguarneri

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    I was talking to Pavel

    Post by gguarneri on Sat May 19, 2018 2:03 am

    05/19 2018-01:55:39

    I am new here, but I have bought several ABQ boards from Pavel.  I have one installed in my VTA-120 along with Bob Latino's time delay board and a highly regulated DC heater board for the heaters of the 12AU7 tubes in the amp.  I also have one installed in my Marantz 8B.  As most of you already know, they work great.

    I additionally installed digital meters where the bias check octal sockets usually go, ST70, ST120, VTA120, and a DPDT switch where the stereo/mono switch would go on a ST70, but is not used in the VTA120, so I can easily check the bias two tubes at a time.  The meters only have two significant digits to the right of the decimal point, so they always read .50 all the the time.  I leave the amp on (KT88s) days at a time, and .50 is always on the meters whenever I check.  Ofcourse, before I installed the meters I use to check the bias at the octal sockets with my multi-meter, which has three significant digits to the right of the decimal point, and there would usually be a variance of +/- 2 or 3 in the third digit to the right of the decimal point; but hey, I'm talking 2 or 3 thousandth of a volt here, so that is really insignificant.  Oh yeah, I installed an on/off switch for the 5Vdc power supply, necessary to power the meters, which is mounted to the bottom of the amp's power transformer inside the amp, so that the meters are only lit when I want to check the bias.  I like it.

    Anyway, I am not great with forums: I usually like to read them, but seldom register and post to them.  However, I was looking at the audioamp.eu site, where I buy most of my ABQ boards now, and I noticed the ABS-Q+ plus board.  I want to use this board in my Marantz 8B, but the information at the site said it requires 230 mains voltage.  So I contacted Pavel to ask if the new module could be used here in the USA.  He got back to me with what seem at first to be not so good news.  He said he was sorry, but it could only be used with 230v.  But then he got back to me again, and said it seems they are going to be introducing the latest modules usable with 115/230v.  He said the new ABS-Q+ modules are going to be the next iteration of the modules, and he mentioned availability in as little as a week or two from now.   He mentioned I should blab about it, so here I am blabbing.  I guess I'll see if there are any other threads (if that's what you call em) about auto bias I can blab on.
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    tubes4hifi
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    Re: Auto-Bias board on Roy's website?

    Post by tubes4hifi on Sat May 19, 2018 11:06 am

    ATTENTION ALL M125 auto-bias users.
    go back to page 4 of this thread and look at revised photo/diagram/instructions.
    Bias connect to AB board needs to be from C17, not from C18, not a huge change but did create a problem.
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    Tubes4ever

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

    Post by Tubes4ever on Sat May 19, 2018 12:52 pm

    pavlikkkk wrote:
    jfine wrote:Pavel again..

    The M125 has the option of only running 2 tubes instead of 4. Will the board function properly when 2 tubes are removed like this?

    Actually, will the amp function properly?
    When using only two end tubes, the primary OT impedance will not be properly adjusted.
    Pavel

    Pavel,

    You still haven't answered Jfine's question. Will the bias board work correctly to control the two tubes in the 125 if the other two tubes are removed?

    I already brought the impedance issue up to Bob awhile back and he said that the impedance difference caused by using two tubes instead of four will not adversely effect the sound.

    But you are correct, the primary impedance will not longer be optimal for the tubes.
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    pavlikkkk

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

    Post by pavlikkkk on Sat May 19, 2018 2:56 pm

    Tubes4ever wrote:
    pavlikkkk wrote:
    jfine wrote:Pavel again..

    The M125 has the option of only running 2 tubes instead of 4. Will the board function properly when 2 tubes are removed like this?

    Actually, will the amp function properly?
    When using only two end tubes, the primary OT impedance will not be properly adjusted.
    Pavel

    Pavel,

    You still haven't answered Jfine's question.  Will the bias board work correctly to control the two tubes in the 125 if the other two tubes are removed?

    I already brought the impedance issue up to Bob awhile back and he said that the impedance difference caused by using two tubes instead of four will not adversely effect the sound.

    But you are correct, the primary impedance will not longer be optimal for the tubes.

    somewhere I wrote it, probably in a private correspondence ...
    You can use M125 with two tubes, AB-Q respects this, if you do not mind that the transfer characteristic of the amplifier will change due to connecting improper impedance to the OT primar.
    But what you can not do:
    when you push the third and fourth tube into the amplifier, the amplifier must not be turned on !! Tubes would be destroyed !
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    tubes4hifi
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    Re: Auto-Bias board on Roy's website?

    Post by tubes4hifi on Wed May 23, 2018 4:09 pm

    seems no one has posted a photo of the auto-bias board in a working amp, so here's a photo of one I installed in a customer amp yesterday, with fuses on each output tube


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

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