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    Auto-bias board and a Weber WS1

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    Kramer

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    Auto-bias board and a Weber WS1

    Post by Kramer on Mon May 14, 2018 6:54 pm

    Apologies if this seems like beating a dead horse, I wanted to get some insite into using a Weber WS1 with the Auto Bias board now available on the tubes4hifi site.

    I am currently using a gz34 with the yellow sheet diode mod and haven't had any issues but would like to use a copper cap to avoid any future catastrophic rectifier failures if possible.

    My understanding is with the auto-bias board the output tubes will slowly be introduced to the HV so the weber would not cause any issues under normal operation with the bias board. Is this correct?

    Also I cannot find info if the yellow sheet diodes should be removed from the rectifier socket before using the weber. Any insite would be greatly appreciated. Thanks.
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    corndog71

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    Re: Auto-bias board and a Weber WS1

    Post by corndog71 on Mon May 14, 2018 8:36 pm

    The yellow sheet diode mod simply puts a pair of UF4007 or 1N4007 before whichever rectifier you plug into the socket. I don’t think it would affect the auto-bias board but I could be wrong.
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    jfine

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    Re: Auto-bias board and a Weber WS1

    Post by jfine on Tue May 15, 2018 10:15 am

    The only issue I heard with the WS1 is it comes up too fast when powering on, you can get them with a thermistor, not sure if that or the slow autobias power up helps the issue.

    The diode mod, I thought that was there mainly so that if there was a power off/power on too quickly, it would stop the power tubes from sending current back to the tube rectifier, so it doesn't blow, the WS1 I think handles it OK, not sure if the AB has anything to do with that.
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    Kramer

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    Re: Auto-bias board and a Weber WS1

    Post by Kramer on Tue May 15, 2018 12:27 pm

    That all makes sense, I did get the thermistor with mine. Thanks for the info.

    New2Tubez

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    Re: Auto-bias board and a Weber WS1

    Post by New2Tubez on Tue May 15, 2018 1:04 pm

    Maybe Roy, Pavel, or Bob could weigh in here. There's more than a little interest.
    Thanks
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    Kramer

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    Re: Auto-bias board and a Weber WS1

    Post by Kramer on Tue May 15, 2018 1:37 pm

    New2Tubez wrote:Maybe Roy, Pavel, or Bob could weigh in here. There's more than a little interest.
    Thanks

    I was able to answer my own questions. I should have searched more previous postings before even posting a new thread.

    http://dynacotubeaudio.forumotion.com/t3430-there-s-a-good-time-to-use-the-weber-ws-1-ss-rectifier?highlight=Weber

    That thread has some good information and deserves a read from anyone interested in this topic.

    Also the thread below specifically on page 3-4

    http://dynacotubeaudio.forumotion.com/t2639p50-weber-wz68-now-not-recommended-on-weber-website?highlight=Weber+ws


    Last edited by Kramer on Tue May 15, 2018 1:55 pm; edited 2 times in total (Reason for editing : Added second link)

    New2Tubez

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    Re: Auto-bias board and a Weber WS1

    Post by New2Tubez on Tue May 15, 2018 2:02 pm

    Hmmmmm. In my case, wall ac comes in at between 119-122+ so my ST-120 is on the recommended 5A variac set to 117vac. That post mentions the opposite- low voltage.  

    So will the WS1 w/thermistor be ok w/ yellow sheet diode mod and the new Auto Bias board w/mini fuses..?  I'm currently w/ 5AR4, no TD board, or AB board.

    Most of this goes over my head but I'm trying to understand and do it right.  Thanks for your patience.
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    Kramer

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    Re: Auto-bias board and a Weber WS1

    Post by Kramer on Tue May 15, 2018 2:21 pm

    One question I am not able to answer, since the WS1 has no sag resistors it will increase B+ and will require the bias to be reset.

    Is the bias level set on the A/B board potentiometer affected by this rise in B+ from the WS1?

    I have not tried yet but I should be able to test by removing all tubes and testing bias points on the A/B board at various levels of incoming voltage with a variarc.
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    Kramer

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    Re: Auto-bias board and a Weber WS1

    Post by Kramer on Tue May 15, 2018 2:47 pm

    New2Tubez wrote:Hmmmmm. In my case, wall ac comes in at between 119-122+ so my ST-120 is on the recommended 5A variac set to 117vac. That post mentions the opposite- low voltage.  

    So will the WS1 w/thermistor be ok w/ yellow sheet diode mod and the new Auto Bias board w/mini fuses..?  I'm currently w/ 5AR4, no TD board, or AB board.

    Most of this goes over my head but I'm trying to understand and do it right.  Thanks for your patience.

    I am going to test the bias board like stated in my previous post and will let you know my findings.

    One part I should mention when you install your bias board and if your using the fuses, make sure your four cathode connections from the A/B board go to pin ONE on all 4 sockets. Then the fuse is used to bridge pin one to eight.

    New2Tubez

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    Re: Auto-bias board and a Weber WS1

    Post by New2Tubez on Tue May 15, 2018 2:52 pm

    Thanks for your help!

    I appreciate the tip on the fuse connections as well.
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    Kramer

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    Re: Auto-bias board and a Weber WS1

    Post by Kramer on Tue May 15, 2018 3:19 pm

    I tested the bias points on the A/B board at 123V my normal line voltage and at 114V. The bias reading from the board remained steady at .506 during both tests.

    This would suggest the bias level set on the board is not affected by line voltage fluctuations and would not need to be reset after switching over to the WS1.

    I will try mine and post results shortly. I think I am also going to rewire the bias test points to the resistors on the A/B board.
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    jfine

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    Re: Auto-bias board and a Weber WS1

    Post by jfine on Tue May 15, 2018 3:31 pm

    Kramer wrote:I tested the bias points on the A/B board at 123V my normal line voltage and at 114V. The bias reading from the board remained steady at .506 during both tests.

    This would suggest the bias level set on the board is not affected by line voltage fluctuations and would not need to be reset after switching over to the WS1.

    Makes sense. But maybe if the plate voltage were to go up, after installing the WS1, then if you were calculating bias setting based on the 70% theory, you may then have to readjust bias anyhow.

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    Kramer

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    Post by Kramer on Tue May 15, 2018 5:00 pm

    jfine wrote: Makes sense. But maybe if the plate voltage were to go up, after installing the WS1, then if you were calculating bias setting based on the 70% theory, you may then have to readjust bias anyhow.

    That is correct, if the plate voltage increases and since the cathode current is used by the A/B board.

    Does this seem correct?
    The amp has around 485V on the plates. Replacing the gz34 with a WS1 whould add an additional 17V to the plates and 70% on a kt88 plate is 29.4watts.

    29.4 / 502 = 0.058

    So the bias by that calculation is up to 580mv.

    But if you use that same formula above I believe Bob recommends biasing kt88s on a st120 at 500mv, so about 24 watts and 485 on the plates, which is about 57%.

    So with using Bobs reduction down to about 57% that would be

    23.94 / 502 = 0.0476

    So to account for the additional voltage from the Weber I would set the bias on the A/B board to 476mv?

    Would any one please let me know if this at all seems correct? I could really use a second set of eyes.
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    jfine

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    Re: Auto-bias board and a Weber WS1

    Post by jfine on Tue May 15, 2018 8:33 pm

    The math seems right,

    I think it depends on what you want, longer tube life or trying to target a KT88 to sound its best? Actually I'm up a little higher than 70% on mine. The autobias should provide longer tube life anyways...
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    10-E-C

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    Re: Auto-bias board and a Weber WS1

    Post by 10-E-C on Tue May 15, 2018 8:48 pm

    I'm wondering what the expectation of a KT120 tube is? I've been running mine almost daily for 3 1/2 years in M125s, I check the bias every month or so when I remember and its right on .500 every time. I do have rock solid AC voltage from TVA and step down to 118VAC running a Mullard GZ37 rectifier tube, no diode mods. I don't see any reason for me to mess with my amps.
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    Kramer

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    Re: Auto-bias board and a Weber WS1

    Post by Kramer on Tue May 15, 2018 9:12 pm

    10-E-C wrote:I'm wondering what the expectation of a KT120 tube is? I've been running mine almost daily for 3 1/2 years in M125s, I check the bias every month or so when I remember and its right on .500 every time. I do have rock solid AC voltage from TVA and step down to 118VAC running a Mullard GZ37 rectifier tube, no diode mods.  I don't see any reason for me to mess with my amps.

    I am not sure what the plate voltage is of the M125's but running kt120's at .500 in a ST120 is running them at 35%. I would guess on/off cycles would add a little extra wear but I would say they will last a long time.

    Jfine, thanks for looking. I am going to leave the bias where it's at and try the tubes biased a little higher with the Weber.
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    deepee99

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    Re: Auto-bias board and a Weber WS1

    Post by deepee99 on Sat May 26, 2018 1:09 pm

    Why not just get a WX-68? They ramp up quicker than tubes but at least there's a delay, unlike the sudden in-rush from the WS-1.
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    Kramer

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    Re: Auto-bias board and a Weber WS1

    Post by Kramer on Mon May 28, 2018 9:05 pm

    WS1 doesn't have a sag resistor so it doesn't get nearly as hot, its available with a thermistor which I got and it works beautifully. I opened it up and can easily replace diodes but I doubt I ever will need to. Polished her up to a near mirror finish as a bonus, I think it looks great.

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    tubes4hifi
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    Re: Auto-bias board and a Weber WS1

    Post by tubes4hifi on Sat Jun 02, 2018 9:38 pm

    PLUULLLL_EZZZZZZ
    do not power up tube equipment with no tubes in it unless you are using a variac set to a lower input voltage.
    Any capacitors that normally see 500v could easily see 600v and blow up in your face !!!!!!!!!!!
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    Kramer

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    Re: Auto-bias board and a Weber WS1

    Post by Kramer on Sun Jun 03, 2018 11:55 am

    Roy, thanks for the reply. I will not start the amp without tubes at regular line voltage again. Thanks for looking out for the guys still learning. I really appreciate this forum.

    I do want to clarify at no time did I have the Weber WS1 installed and then powered up the amp. I removed all tubes as well as the WS1 before powering up and taking measurements.

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