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    Auto-Bias board on Roy's website?

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    ericoto

    Posts : 6
    Join date : 2013-12-11

    M-125 autobias board assembly

    Post by ericoto on Sun Sep 09, 2018 7:55 pm

    Just finished M-125 autobias boards. Was a bit harder then I anticipated, I don't see much feedback on installation, but fit is tight. If you choose to try, my advice is First remove C6 & C8 coupling capacitors and sit as close to board as possible when I assembled the M-125 I kept them fairly high, I also covered them with heat shrink tubing. Could it be possible to substitute a small capacitor for C6 and C8? Second, Keep wires longer then you think for connections between A/B and driver board, I had redo 2 as they were too tight though I had plenty of lead. Third, I soldered all the wires on the bias board, then attached to driver screws, made rest of installation easier.  Just my thoughts and I did not see any other feedback. I had all blue lights after installation. Nice soft start up. No listening tests yet. I am an experienced kit builder but by no means an engineer, so it is possible for casual builder.
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    LeGrace

    Posts : 258
    Join date : 2016-08-07
    Location : Ontario, Canada

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

    Post by LeGrace on Mon Sep 10, 2018 5:16 pm

    Interested in this mod for my M125's. Any additional details would be appreciated, pics also if possible.
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    tubes4hifi
    Admin

    Posts : 1476
    Join date : 2008-11-30

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

    Post by tubes4hifi on Sat Sep 15, 2018 10:47 pm

    still no photos from someone with an M125 amp?? I've sold at least 6 pairs of these, someone please post photos showing the install to help newbies . . .

    ericoto

    Posts : 6
    Join date : 2013-12-11

    M125 Autobias board installation

    Post by ericoto on Sun Sep 16, 2018 11:53 am

    Here'ss a photo I took after my recent installation, installation not too bad although is tight, See above notes, would advise removing coupling capacitors and getting as close to board as poosible, I covered mine in heat shrink tubing to prevent any shorts from metal case. Also I found it easier to attach wires to C17 capacitors when replaced than try to solder later, I just soldered close to body of capacitor. Also I attached all wires to the AB board first, labeled, installed board and soldered to M125 sockets. Saved time. Hope this helps I have attached a single photo, only took 1, I did blow the copper top after installing, likely unrelated, case was loose. If I reassemble will post more photos




    New2Tubez

    Posts : 21
    Join date : 2018-03-20
    Location : NY

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

    Post by New2Tubez on Sun Sep 16, 2018 5:44 pm

    Probably not applicable but I got the AB board for my VTA 120 maybe 4 months ago.

    I haven't installed it yet because the room I solder in is currently an un-airconditioned 78 degrees with 69 percent humidity. It was 85 in August. I'm waiting 'til it gets a bit cooler. I also intend to relocate the 4 LEDs to the VTA board (much dimmer ones). As advised, I will heat shrink the K40 PIO caps as well. Will also use a S/S Weber WS-1 instead of the 5AR4.

    It sounds so great that I'm not in a real hurry!

    Hope your's goes well. I'll post once it's done.
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    deepee99

    Posts : 2005
    Join date : 2012-05-23
    Location : Wallace, Idaho

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

    Post by deepee99 on Sun Sep 16, 2018 6:11 pm

    If this is the same board Don Sachs is using in his ST-120 (Kootenay) amps, you will be blown away. I have had mine now since August of last year and it absolutely sings.

    New2Tubez

    Posts : 21
    Join date : 2018-03-20
    Location : NY

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

    Post by New2Tubez on Sun Sep 16, 2018 7:08 pm

    deepee99 wrote:If this is the same board Don Sachs is using in his ST-120 (Kootenay) amps, you will be blown away. I have had mine now since August of last year and it absolutely sings.

    From the looks of the last pic on the KT88 amp, the center green board seems identical to mine. The transformers and most of the other stuff don't, but I'm thrilled just the same.
    Enjoy the sound..!

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

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