Specs for new PT to the A15Mk2

    Most of the problems with my A15Mk2 Deluxe ampkit are now solved (still waiting for certain parts from Klaus though...) and the amp has turned out amazing. *

    I´m so pleased with it that I want to convert it to a 50W amp using 2xEL34s or 2x6L6s.
    Picking a new OT will be no problem, but I need help in picking the right PT!

    I will need about 450V on the powertues which means that I´ll need about 480V DC powersupply.

    What is needed for the switching system?
    This: Vsec2 = 20 V/0,12 A

    I´ve seen these values regarding the stock PT:
    Vpri = 230 V no tap
    Vsec1 = 230 V/0,12 A
    Vsec2 = 20 V/0,12 A
    Vsec3 = 6,3 V/4 A

    I´m really lousy at specifying what is needed (mA for example) so please help me choosing the right PT for my upcoming 50W (EL34) Madamp!


    * I´ve modded the amp more towards a classic rock sound as well as having added an extra preamptube for the fully tubedriven parallel custom FX-loop.

    Maybe MAD could help me out here!?

    I´m in contact with the company making the PT that comes with the kit, but they need exact specifications of the PT in order to recommened an existing one from their line of products or making me a custom model.

    Hi,

    Zitat

    Picking a new OT will be no problem

    so if you know this what means you know the operation point/parameters of the chosen tubes (Va, Ia and resulting from this Vg1_bias) you can estimate the needed current and voltage.

    Someone else can't do this for you because he don't know the parameters you have chosen for operating the new output tubes...

    Taken twice Ia and adding some mA for the preamp multiplying by 1,2...1,5 you get the current for the HV winding.
    Assuming you use SS rectifier you take Va adding Ia · Rxf_dc and a few volts for RC regulation and divide this by 1,414 you get the voltage of the HV winding.

    Adding all heater currents plus some 100 mAs for lamps etc. you get the current of the heater winding.

    If you use a separate winding for the bias voltage it should at least have the same voltage (Vac) as the DC bias voltage Vg1_bias in the operation point.
    50 mA will be sufficient (if you use it only for bias).

    If you calculate the sum of the power (V · I) of each secondary winding you know the "VA" the power transformer must have.

    Bernd

    Jaichweiß (Andy Pipkin)

    Thanks for your reply!

    I know that my knowlege about these mattern aren´t enough, but I´m doing my best ;)

    I believe that this would be a working PT for my needs:

    Primary:
    220V-230V-240V @ 50Hz

    Secondary:
    330-0-45-330V @ 200mA
    3,15V-0-3,15V @ 5A

    OK, now the problem is that the switchingsystem was powered by 20V taken from the 6V6 bias voltage tap and now there´s 45V, needed for the EL34 bias...

    What will happen to the switching system?
    Is there a way around his problem?

    Hi,

    my advice: If there is no Xformer with an additional winding for switching don't use any cheap trick on the Transformer just take a small 12 V onboard transformer to supply all the relays and blinky LEDs ;)

    If you use this kind of relay, each relay will draw about 17 mA of current. So, with a very small 1.8 VA Transformer you can supply up to five of these relays.

    Bernd

    Jaichweiß (Andy Pipkin)

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