EZ81 power supply

paltal

Member
2016-04-02 1:41 pm
hi
i am new here, so i'll be Grateful for your patience and your help as well
i am trying to build a power supply for a 12b4 preamp line level to drive my dynaco st70.

i want to use an ez 81 (have some not in use) and a choke
i need some help with the tran and ps specs, there is a local shop that i can give the specs and they can wind a tranformer
i aded a schema for the ps this is from my limited understanding and stuff I picked from the net, i marked ''?'' were i'm not sure....dont know:eek:

thank you all
 

Attachments

  • 12B4pre.gif
    12B4pre.gif
    3 KB · Views: 562
  • ps 81.jpg
    ps 81.jpg
    354 KB · Views: 562

tasos25

Member
2013-02-13 1:19 pm
hi
i am new here, so i'll be Grateful for your patience and your help as well
i am trying to build a power supply for a 12b4 preamp line level to drive my dynaco st70.

i want to use an ez 81 (have some not in use) and a choke
i need some help with the tran and ps specs, there is a local shop that i can give the specs and they can wind a tranformer
i aded a schema for the ps this is from my limited understanding and stuff I picked from the net, i marked ''?'' were i'm not sure....dont know:eek:

thank you all

PSUD2
 

artosalo

Member
2010-02-16 9:00 am
I would order a power trafo with the following specifications:

Primary 1: 300 V - ct - 300 V, 50 mA ( 30 VA)
Primary 2: 6,3 V, 1.5 A for EZ81 (9.5 VA)
Primary 3: 6.3 V with ct, 2A for 12B4s (12.5 VA)

The size of the transformer would be some 60 VA.

The reason I suggested (primary 3) 6,3 V with ct for 12B4s is that there is no reason to have DC-heaters with line level preamp.

But if you want to have DC-heaters, then I suggest to use 12.6 VDC regulated with 7812.
The suitable primary would be some 15 V, 1A.
 
An EZ81 can easily feed a couple of 12B4. As artosalo said, no need for DC heaters - just learn how to do AC heater wiring.

The EZ81 heater winding, like all heater supplies, should have a DC reference. Two options:
1. Put all valves on one heater winding, and ground either one side or the centre-tap.
2. Connect the EZ81 heater winding to the EZ81 cathode.
 

artosalo

Member
2010-02-16 9:00 am
...and ground the c tap like this ?

Yes. It will work for sure.
And connect the cathode and heater of the EZ81 together.

Usually you would lift the center tap via a voltage divider...

Maybe sometimes, but in this case when the cathode is at low potential it is not necessay.
I have used solely grounded CT of the heaters in this kind of circuits without a sign of hum problem.
 

paltal

Member
2016-04-02 1:41 pm
proceeding

hi again

for the cathode capacitor i got a pair of nichicon muse 330 microF \ 25v
and a pair of the same with 470 microF \ 25v ( instead of the 360uf in the schema )
will there be an audible Difference between the pairs?
i am considering using both with a toggle switch for ''live Trial and error'' ...?

meanwhile metal work in progress...
 

Attachments

  • SAM_0989.jpg
    SAM_0989.jpg
    522.3 KB · Views: 202
  • SAM_0988.jpg
    SAM_0988.jpg
    458.1 KB · Views: 196
I have seen a 6S4 and EZ81 became unusable because a short circuit between cathode and heater. Since this experience, I like to have the cathode and heater at the same potential, but not directly connected together. How?

Well, wiring a high value resistor between them, and (optionally) decoupling it to ground. Something like this. Yes, I'm still using edit with DOS!, but understandable.
 

Attachments

  • PS.GIF
    PS.GIF
    22 KB · Views: 164