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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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dalemurray
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Tom Pickett
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    Analog Bias Meters For The VTA ST-120

    Tom Pickett
    Tom Pickett


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    Post by Tom Pickett Wed Mar 10, 2021 10:26 pm

    Good afternoon everyone.... I hope all of you are having a good day.

    I have another little project that I'm working on for the VTA ST 120.

    I am trying to keep everything as much as original as possible especially the front face of the chassis on the amp. I also want to keep the original octal bias sockets on the front of the amp.

    The new project I'm working on is I want to buy two octal male socket plugs to plug into the female octal sockets on the front of the amp. On the two octal male plugs I want to install some calibrated electronics and two analog meters inside the plugs to monitor the bias of the tubes.  
    This way I can unplug the bias meters when I'm not using them and plug them in when I want to adjust or monitor the bias and/or leave the plugs in for aesthetics.

    I found two plugs on eBay and a few others that I have pictured below.

    The only problem I have is I am limited to my knowledge and resources to find small enough analog meters that will fit snugly inside the plugs and was wondering if any of you here might know where I can find two small analog bias meters the same size as those plugs  ?
    I have already seen a few digital meters but I would like to see if I could stay analog.

    Have a good day everyone.

    Analog Bias Meters For The VTA ST-120 S-l16024
    Analog Bias Meters For The VTA ST-120 S-l16025
    Analog Bias Meters For The VTA ST-120 S-l16026
    Analog Bias Meters For The VTA ST-120 S-l16027
    Analog Bias Meters For The VTA ST-120 S-l16028

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    Tom Pickett
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    Post by Tom Pickett Wed Mar 10, 2021 11:18 pm

    I just now found 2 of these very nice antique Brown Bakelite Octal Socket plugs..... love it and just bought both of them.

    Still looking for 2 very small analog voltage meters to fit inside the plugs.

    Analog Bias Meters For The VTA ST-120 Screen10

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    Rbertalotto


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    Post by Rbertalotto Thu Mar 11, 2021 11:10 am

    Hi Tom, Great idea! I looked extensively for meters small enough to fit into those socket holes. No luck with analog meters but I did find digital meters that would fit. I'm just not sure a digital meter that reads 0-25V would have enough resolution for .5V. I ordered a couple analoge, vintage looking meters from Ebay by way of Hong Kong.....But they will be mounted in a custom wood base and not the front panel.

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    Rbertalotto


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    Post by Rbertalotto Thu Mar 11, 2021 11:14 am

    With this meter you could monitor both tubes simultaneously.

    https://www.amazon.com/MICTUNING-Digital-Voltmeter-Voltage-Monitor/dp/B0721PQCKD/ref=sr_1_4?crid=TLOZ169OO11R&dchild=1&keywords=round+dc+voltage+meter&qid=1615475513&sprefix=round+dc+meter%2Caps%2C286&sr=8-4

    I've used these meters extensively in many projects. They are quite tiny

    https://www.amazon.com/Voltage-Waterproof-Voltmeter-Compatible-Motorcycle/dp/B08TWW8MKJ/ref=sr_1_5?crid=TLOZ169OO11R&dchild=1&keywords=round+dc+voltage+meter&qid=1615475588&sprefix=round+dc+meter%2Caps%2C286&sr=8-5

    Do a search on Amazon for "round dc voltage meter"


    But look at the specs. The second meters I posted said:

    Measuring range: 6-36 V DC
    Working voltage: 12-24 V DC

    NoGood

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    Tom Pickett
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    Post by Tom Pickett Thu Mar 11, 2021 12:09 pm

    Yes..... yesterday I found the same second meter you just now posted and was looking at it but to me it looks kind of like cheesy cheap plastic lol.....

    Thanks Rbertalotto for your help.
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    Basidio


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    Post by Basidio Thu Mar 18, 2021 3:35 pm

    Hello,
    I believe this could be a potential solution. If you start with a meter similar to the Baomain 65C5 Analogue Panel Meter (search it on Amazon, sorry I'm new to this forum and can't post links for 7 days)..

    And then modify the Resistor value to get a desirable range as shown in the youtube video titled:
    "DIY Analog Voltmeter" posted by Kasyan TV

    Perhaps with some tinkering you could come to a custom solution. Just an idea, but it seems like you could modify the housing of an analog voltmeter to better fit your application, or take the internals of an ugly analog meter and re house them in something more desirable.
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    Rbertalotto


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    Post by Rbertalotto Thu Mar 18, 2021 3:40 pm

    No need to modify the meter with a resistor. These meters you reference are available in 0-1v, 0-3v, 0-10v, 0-15v, etc....

    I'm using the 0-1v version and it works great when compared to my Fluke VOM.

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    sKiZo
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    Post by sKiZo Thu Mar 18, 2021 5:02 pm

    Rather than trying to fit analog meters into the sockets, how about an add on box large for what's commonly available? Yes - it will change the look of the chassis, but you'd only need to plug it in when actually testing or adjusting the amp.

    PS - I went with a custom case, so no problems fitting things in. You WILL want to adjust your bias without the meters in place, then match those readings to the meters. You'd be surprised how much error the additional hardware will make. I ended up having to add adjustment pots to the meter circuit to compensate for the additional signal.

    Analog Bias Meters For The VTA ST-120 Meters-backs-4vr2

    Analog Bias Meters For The VTA ST-120 Meter-error

    Oh. And you'll probably notice I used mA meters - a simple snip of an internal load resistor makes them mV ...

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    dalemurray
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    Post by dalemurray Thu Mar 18, 2021 6:41 pm

    I bought a pair of vintage meters.
    One for each side with a toggle switch for front or read tubes.

    I just had to determine the correct resistor to get the reading to make sense.

    Analog Bias Meters For The VTA ST-120 Meters10

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    Post by Hefalcon Fri Mar 19, 2021 1:33 am

    I bought 2 meters, a small box. Have a switch on the back and wires with a socket on the ends that plug into the backs of my MK3's I built.

    Analog Bias Meters For The VTA ST-120 Meter010

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    Post by edman44 Tue Jun 22, 2021 7:17 pm

    Evening Tom,
    I was wondering if you had any success in finding the Bias meters? I also am looking for a set of analog meters for my new VTA-ST120 KIT that I just received on Monday.
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    Post by teftamaqua Sun Nov 07, 2021 11:25 pm

    tubes4hifi
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    Post by tubes4hifi Fri Nov 12, 2021 6:59 pm

    these are nice and small but you would need to supply power to them, you could use the 6vac filaments and a diode and cap and power them with 5-6vdc thru the sockets
    https://www.amazon.com/HiLetgo-Voltage-Digital-Voltmeter-Motorcycle/dp/B079N98PY4

    Sponsored content


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