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    tomiko transformer

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    bdl marine

    Posts : 12
    Join date : 2012-05-24

    tomiko transformer

    Post by bdl marine on Thu May 24, 2012 7:51 pm

    I have recently built a st70 clone. I am using a tomiko pt-st-70 111 pwr transformer and two 1650na hammond output transformers. I purchased a choke from triode and the cap board also. I am using the pc3 with rewired tube sockets to utilize phillips 6u8a drivers. The output tubes are electro harmonix and the rectifer is jj gz34. The amp sounds great. This is my first tube amp so I am very happy with the outcome. My question/problem is the pwr transformer seems to run hot. After about 3-4 hours of use at moderate to low volume the transformer can be touched but just barely. Is this normal of is there a problem. I am using psb t1 speakers and a parasound p3 pre

    hawaii.ken

    Posts : 157
    Join date : 2012-01-31

    Re: tomiko transformer

    Post by hawaii.ken on Thu May 24, 2012 10:51 pm

    What current do you set for your output tubes?

    bdl marine

    Posts : 12
    Join date : 2012-05-24

    Re: tomiko transformer

    Post by bdl marine on Thu May 24, 2012 11:10 pm

    fixed at 265ma

    bdl marine

    Posts : 12
    Join date : 2012-05-24

    Re: tomiko transformer

    Post by bdl marine on Thu May 24, 2012 11:12 pm



    120V input

    Heavy duty output for:

    365--60--0--365V (265mA)

    0-5V (4A)

    3.2--0--3.2V (3A)

    3.2--0--3.2V (3A)

    hawaii.ken

    Posts : 157
    Join date : 2012-01-31

    Re: tomiko transformer

    Post by hawaii.ken on Fri May 25, 2012 4:05 am

    You need to measure the current for each output tube. Most ST-70 clones have a 10-ohm cathode resistor connecting the output tube's cathode to ground so you can measure the voltage across the resistor to get the current being drawn by the tube.

    I think 55-57ma for each tube is the recommended level (.55v-.57v accross the 10-ohm resistor).

    It would be helpful if you would post a schematic for your amp.


    bdl marine

    Posts : 12
    Join date : 2012-05-24

    Re: tomiko transformer

    Post by bdl marine on Fri May 25, 2012 6:10 am

    I will do that tonight. I see where you are going with this. Thanks and I will provide that info later

    bdl marine

    Posts : 12
    Join date : 2012-05-24

    Re: tomiko transformer

    Post by bdl marine on Fri May 25, 2012 2:43 pm

    There is only one resistor per channel. Pins 1 and 8 to pins 1 and 8 through resistor to ground. This is part of the bias circuit I believe.I have 1 volt per side across the resistor as per the bias set-up instructions.

    hawaii.ken

    Posts : 157
    Join date : 2012-01-31

    Re: tomiko transformer

    Post by hawaii.ken on Fri May 25, 2012 4:08 pm

    bdl marine wrote:There is only one resistor per channel. Pins 1 and 8 to pins 1 and 8 through resistor to ground. This is part of the bias circuit I believe.I have 1 volt per side across the resistor as per the bias set-up instructions.


    What value resistor?

    Again, a schematic for your amp would be helpful.

    bdl marine

    Posts : 12
    Join date : 2012-05-24

    Re: tomiko transformer

    Post by bdl marine on Fri May 25, 2012 7:09 pm

    10 ohm 1w

    bdl marine

    Posts : 12
    Join date : 2012-05-24

    Re: tomiko transformer

    Post by bdl marine on Fri May 25, 2012 7:11 pm

    schematic is the same as original but with a triode cap board

    hawaii.ken

    Posts : 157
    Join date : 2012-01-31

    Re: tomiko transformer

    Post by hawaii.ken on Sat May 26, 2012 2:09 am

    A 10 ohm resistor would give you 50ma per tube which is in the ballpark.

    You can try reducing the bias to .90volt (.45ma per tube) to see if it helps with the heat problem.

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