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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


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peterh
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    Dumb Question on Setting Bias

    peterh
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    • Post n°26

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    Post by peterh Thu Nov 24, 2016 12:12 pm

    Dave_in_Va wrote:Is there anywhere to buy a cover for the board that's ready to go? I just dislike the look of those cages.

    I've seen pics here where the board was covered with a piece of glass or something (with holes for the three tubes, bias pots, etc.

    Thanks.

    http://www.dynakitparts.com/dynakit-products/covers
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    pedrocols
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    • Post n°27

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    Post by pedrocols Thu Nov 24, 2016 12:20 pm

    I second bluemeanies.  I also use a ceramic screwdriver that you can get very cheaply.
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    Peter W.
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    • Post n°28

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    Post by Peter W. Thu Nov 24, 2016 2:48 pm

    GP49 wrote:Peter:

    Among the stuff that came out of that basement, along with the hundreds of tubes you picked up, were a Simpson 260 VOM and an RCA Senior VoltOhmyst VTVM.  I couldn't resist keeping them, though I will probably never use them, beyond putting them back to original performance.

    I drew the line at the Tektronics scope dating from 1948, though.  Could hardly lift it and its bandwidth would not have been enough to align the RF and IF of the Pilot FM tuner I salvaged.

    You will use the Simpson, at least. There is something about a mirrored analog meter for audio use, aligning and several other tasks that come to mind, where needle dither is important information. Yes, my Fluke has a bar indicator, but not really the same thing.

    Some will state that a VTVM is required for proper alignment of vintage equipment, as the settings on the alignment charts were based on a VTVM. Not so much in my experience. The Fluke works just fine. After all, one is centering to a signal.

    Good call to keep them in any case!
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    mkcarnut
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    • Post n°29

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    Post by mkcarnut Thu Nov 24, 2016 3:00 pm

    So, dumb question #2...I was just looking at multimeters, and I realized there is a huge range of options even just with Fluke. And there is a huge range of costs...for setting bias, what is the least I need and what are the issues with the cheapos that led folks to say things like Fluke or junk?

    Thx...Mark
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    Tube Nube
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    • Post n°30

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    Post by Tube Nube Thu Nov 24, 2016 6:40 pm

    I use junk, myself. Just a cheapo I got online for $30, or was it $7.99? It seems to work fine.
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    Kentley
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    • Post n°31

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    Post by Kentley Thu Nov 24, 2016 10:34 pm

    If all you need is a machine to test bias, and perhaps to check the occasional speaker wire or interconnect for continuity, and to perform the vital function of monitoring your line AC, there's probably no need to spend more than $30. Readings from my Fluke are virtually identical to readings from my cheapo. What is important is the quality of the test probes. And keeping them clean. Unless you are performing more advanced tasks than those mentioned just keep doing simple and verifiable tests to make sure you are getting the Truth. Short the leads - get zero ohms. Test a battery. Stick the leads up each nostril - the voltage should remain constant, though reversed in polarity. Skip the last test. You'll only foul the probes, and your nose. affraid
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    Tube Nube
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    Post by Tube Nube Thu Nov 24, 2016 11:07 pm

    Surely it requires a Fluke to properly ascertain the voltage drop across the nasal septum. Undignified a chore as it is for the venerable Fluke.
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    quad44
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    • Post n°33

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    Post by quad44 Thu Nov 24, 2016 11:13 pm

    For mckarnut:

    I love building stuff so I took the approach that I would have dedicated bias meters for my MK111s instead of dragging out the multimeters everytime. I found 4 digit digital panel meter kits and mounted them side by each as you see in the picture and they are now part of my system and always on. You can search for these panel meters on Amazon as there are a few options/vendors. For mine I had to change two resistors for proper scaling and I use a single wall wart to power all 4 meters. Here is the link to what I used. https://www.canakit.com/4-digit-led-voltmeter-kit-ck148-uk148.html. The price is in Canadian $s.

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    For the old timers like myself who love their meters here are mine.The two on the left, RCA VTVM and Simpson 270 go far back as 1966. The Fluke is from the early 80's. I just had to add my voice to this post that flat meters are still alive and well.

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    deepee99
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    • Post n°34

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    Post by deepee99 Fri Nov 25, 2016 3:37 am

    I think Skizo did the same thing with his souped-up ST-120, and had to do the same resistance compensation/experiments. I don't mind hauling the old Fluke out every week or two to check bias on my M-125s but meters would look cool. BTW, nice looking set-up.
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    mkcarnut
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    Post by mkcarnut Fri Nov 25, 2016 8:29 am

    Thank you all! Off to Amazon to shop...and when it arrives, I will only attempt the nasal passage test if my sneezing clears up. Would not be a good idea to sneeze with the probes in place.

    Mark
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    Kentley
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    Post by Kentley Fri Nov 25, 2016 8:43 am

    Snot a good idea, Mark.
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    deepee99
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    Post by deepee99 Fri Nov 25, 2016 9:00 am

    mkcarnut wrote:Thank you all!  Off to Amazon to shop...and when it arrives, I will only attempt the nasal passage test if my sneezing clears up.  Would not be a good idea to sneeze with the probes in place.

    Mark

    Be sure to ground yourself first, so you get the full experience.
    Remember, only God makes Flukes. Everything else is a mistake.
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    mkcarnut
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    Post by mkcarnut Fri Nov 25, 2016 2:31 pm

    LOL!
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    Roy Mottram
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    Post by Roy Mottram Sat Nov 26, 2016 3:16 pm

    I'm a cheapskate, I've got four or five meters that cost me $4-$10 each.  Plus one decent $40 meter to insure the cheap guys aren't lying to me.
    If I could afford a Fluke, well, I'd likely buy a quad of Genelex Gold Lions first.
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    deepee99
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    Post by deepee99 Sun Nov 27, 2016 2:06 pm

    Dave_in_Va wrote:Yes, I like my cat more than a freakin' tube.
    I just ordered a cover for the ST70 (in black).

    Yeah, Dave. I'm rather fond of our cat, too, which is why the amps are well off the floor on a slick-sided cabinet. Gawd save our speaker grills, though Smile
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    Dave_in_Va
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    Post by Dave_in_Va Wed Nov 30, 2016 8:07 pm

    Seems since I spent the bucks on it, I kind of like it now. I was really pleased with the quality and fit (perfect). I'm probably not going to attach the Dynaco emblem.

    No hum and my kitty is now safe. One less thing to worry about!

    Thanks.

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    deepee99
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    Post by deepee99 Thu Dec 01, 2016 6:03 am

    Dave in VA,
    Looks like an elegant solution to me, and I'm glad the kitty is now safe.
    I wouldn't want to sacrifice my cat to output tube voltages, either. Fortunately she's about 15 years old and a big jump for her is about 6 inches.
    Did you powder-coat that cage? Almost looks like it.
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    Dave_in_Va
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    • Post n°43

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    Post by Dave_in_Va Thu Dec 01, 2016 10:35 am

    No, that's the stock black cage from Dynakitparts. I don't know what kind of finish it is but it's a very nice matte black.

    Now, since it'll be a major hassle to remove the cage every time I want to check the bias, I'm going to have to modify my small screwdriver (hack the plastic handle down) so it'll fit through one of the holes in the cage and reach the bias pots. Should be easy. I think.
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    Kentley
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    Post by Kentley Thu Dec 01, 2016 11:01 am

    Dave - it is not necessary under most conditions to actually screw down the cage. Placed gently on the chassis, it should nestle quite nicely in the groove between top and bottom. Loosening the screws a bit will widen this gap if necessary, so that you can achieve maximum stability.
    Down side: you may hear a sharp "ping" from the cage on startup. This is not dangerous and is caused by an electromagetic flux from the trannies.
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    deepee99
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    Post by deepee99 Thu Dec 01, 2016 11:21 am

    The flux-capacitor. I feared this would come up. Beam me down, Scotty.
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    Dave_in_Va
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    Post by Dave_in_Va Thu Dec 01, 2016 12:35 pm

    My bias pot access problem was solved by dremelling off the bottom inch and a half of the orange plastic handle. It fits perfectly through the holes in the cover and reaches the pot now.
    I just have to be careful (i. e. sober) when I adjust the bias so as not to touch anything besides the pot with the screwdriver.

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