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    What are the current resistor values and power ratings for the Hi-gain (12AT7) and Lo-gain (12AU7) (12BH7) VTA MKIII/IV upgrade boards?

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    Austuriano

    Posts : 7
    Join date : 2012-11-13
    Age : 67
    Location : Tampa, Florida

    What are the current resistor values and power ratings for the Hi-gain (12AT7) and Lo-gain (12AU7) (12BH7) VTA MKIII/IV upgrade boards?

    Post by Austuriano on Fri Oct 04, 2013 6:46 am

    The values and power ratings have changed over the years, so I would like to know, what are the current recommended values ?

    Bob Latino
    Admin

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    Re: What are the current resistor values and power ratings for the Hi-gain (12AT7) and Lo-gain (12AU7) (12BH7) VTA MKIII/IV upgrade boards?

    Post by Bob Latino on Fri Oct 04, 2013 8:13 am

    Austuriano wrote:The values and power ratings have changed over the years, so I would like to know, what are the current recommended values ?
    Hi Michael,

    All the resistors on the older higher gain VTA 12AT7 driver board were 1/2 watt resistors. Since 12AU7 type tubes draw more current than 12AT7 type tubes, some of the resistors on the newer CCS (12AU7) board are 1 watt (R15 and R16) and a few are 2 watt resistors. (R11 - R14 and R19 - R22).

    Bob

    Austuriano

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    Join date : 2012-11-13
    Age : 67
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    Re: What are the current resistor values and power ratings for the Hi-gain (12AT7) and Lo-gain (12AU7) (12BH7) VTA MKIII/IV upgrade boards?

    Post by Austuriano on Fri Oct 04, 2013 8:33 am

    I received a list from Roy that in the 12AU7 lo-gain configuration had R4,30-32 listed as 221K 3 watt.  My first thought was that a 221K - 3 watt is going to be a physically big resistor particularly in the R4 spot.  I checked, an the R221K is not that common, 220K is more common.  I thought the bias resistors were originally 270K  1 watt, and then changed to 220K  1 watt.  What is the voltage on these resistors, I believe the current is low?.

    Update:  3 is the quantity of resistors, not the watt rating. My mistake


    Last edited by Austuriano on Fri Oct 04, 2013 9:39 pm; edited 1 time in total

    arledgsc

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    Location : SF Bay CA

    Re: What are the current resistor values and power ratings for the Hi-gain (12AT7) and Lo-gain (12AU7) (12BH7) VTA MKIII/IV upgrade boards?

    Post by arledgsc on Fri Oct 04, 2013 8:07 pm

    221K is a standard value for 1% resistors in case you are searching but may not find that close tolerance in higher power resistors.  You can find 220K in 5% tolerances which is probably close enough and would be cheaper as well (usually).

    Austuriano

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    Age : 67
    Location : Tampa, Florida

    Re: What are the current resistor values and power ratings for the Hi-gain (12AT7) and Lo-gain (12AU7) (12BH7) VTA MKIII/IV upgrade boards?

    Post by Austuriano on Fri Oct 04, 2013 9:31 pm

    You are right about the 221K 1% being available in lower wattage, when you get over one watt, your options narrow quickly.  I did realize that the 3 behind the 221K is the quantity, not the power rating.  I was thinking that it was going to be a bear to stick a 3 watt resistor in the R4 position.  Basically the values haven't changed all that much.  I saw one post were Roy mentioned that R30, 32 values have been as high as 270K and 150K on the low end depending on whether or not it was high or low gain.  I believe he also said R39 has a large range

    tubes4hifi
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    Re: What are the current resistor values and power ratings for the Hi-gain (12AT7) and Lo-gain (12AU7) (12BH7) VTA MKIII/IV upgrade boards?

    Post by tubes4hifi on Sun Oct 06, 2013 11:59 pm

    here's the complete parts list from the 2009 version of the VTA70 board, which is identical to the MK3-MK4 boards of that era,
    last time the high gain board was used, with the changes below for the newer low gain version
    this is NOT the parts list for the current version CCS board introduced 18 months ago (early 2012)
    ALL resistors are 1/2 watt unless noted otherwise

    VTA70 driver
    HI gain with 12AT7
    ITEM VALUE QTY
    PCB 1
    R5 & 6 100 2
    R27 & 28 1K 2
    R9 & 10 2.2K 2
    R7,8,15,16  7.5K 4
    R1,2,39 10K 3
    R17 & 18 12K 2
    R37 & 38 27K 2
    R19 - 22 51K 4
    R11 & 12 68K 2
    R13 & 14 150K 2
    R3 & 4 221K 2  (or 220K)
    R29-32 221K 4  (or 220K) (use 150K for MK3)
    R23-26 1M 4
    R40-43 10  1w 4

    V1-3 12AT7 3
    VS1 - 3 9p pcb 3
    VR1 - 4 50K 4
    VR5, 6 10K 2
    C9 & 10 not used 2
    C11 & 12 220 pF 2
    C13 - 16 33uF 450v 4
    C17 100uF 100v 2
    D1 UF4007 1
    C1 - 4 .10 400v 4
    C5 - 8 .33 600v 4
    1/4" hex spacer 4
    1/2 x 4-40 screw 4



    VTA70 driver
    LO gain with
    12AU7 or 12BH7 Change the following parts
    ITEM VALUE QTY
    R27 & 28 470 2
    R9 & 10 1K 2
    R15 & 16 6.8K 1w 2
    R17 & 18 12K 2w 2
    R11-14 33K 2w 4
    R19-22 30K 2w 4
    V1-3  12AU7 or 12BH7  3

    Austuriano

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    Re: What are the current resistor values and power ratings for the Hi-gain (12AT7) and Lo-gain (12AU7) (12BH7) VTA MKIII/IV upgrade boards?

    Post by Austuriano on Mon Oct 07, 2013 6:47 am

    Would you know where to source a 30K 2 watt 1% resistor?Everywhere I have look they are a non-stocked item.  Same with the 221K/220K resistor in the 2 watt.

    Bob Latino
    Admin

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    Re: What are the current resistor values and power ratings for the Hi-gain (12AT7) and Lo-gain (12AU7) (12BH7) VTA MKIII/IV upgrade boards?

    Post by Bob Latino on Mon Oct 07, 2013 9:17 am

    Mouser Electronics sells 30K 2 watt resistors ... Link below ...

    Note - these are 5% resistors - not 1% but I have found them to be much closer together in value than 5%

    30K 2 watt resistors at Mouser Electronics

    These are 30K 2 watt metal OXIDE resistors not metal film. Metal oxide resistors are smaller for their wattage size than metal film. A metal film resistor of 2 watt size will not fit the lead spacing on the driver board unless you bend the leads at an awkward angle.

    Bob

    tomlang

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    Join date : 2009-08-12

    Re: What are the current resistor values and power ratings for the Hi-gain (12AT7) and Lo-gain (12AU7) (12BH7) VTA MKIII/IV upgrade boards?

    Post by tomlang on Mon Oct 07, 2013 10:56 am

    I've had good luck with these 2% resistors and they fit the board fine.

    http://www.mcmelectronics.com/product/440-30K

    Also, if one were so inclined, is it possible to purchase the OLD 2009 VTA board (the one without the CCS) or is this item no longer stocked?

    Austuriano

    Posts : 7
    Join date : 2012-11-13
    Age : 67
    Location : Tampa, Florida

    Re: What are the current resistor values and power ratings for the Hi-gain (12AT7) and Lo-gain (12AU7) (12BH7) VTA MKIII/IV upgrade boards?

    Post by Austuriano on Mon Oct 07, 2013 12:12 pm

    Thanks Bob and Tom for the heads up!  Tom FYI, I discovered that Radio Shack also sell the same resistors online for only $1.86 for a pack of 10, and their shipping is 6.99.  If your need/buying less than 10, that works out to .19 per resistor which is a decent price.  MCM's less than 10 price is .41 per piece, I also thought MCM was a little steep on their shipping charge of $9.49.  I don't know anything about NTE resistors as far as quality goes.  The last mom and pop electronics store in my area use to carry NTE, sadly the store is gone. I never remember to look at RS anymore since all the walk in stores have become cell phone outlets, staffed by people that know less than nothing about electronics.  Thanks for heading me in the right direction!

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