EZ81 power supply

[paltal]

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😱

thank you all

 

[tasos25]

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😱

thank you all

PSUD2

 

[artosalo]

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.

 

[artosalo]

This would be quite perfect transformer and readily available:

http://www.inmadout.com/download/pdf/TA84M18.pdf

 

[DF96]

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.

 

[paltal]

many thanks!
it is cheaper for me to wind localy (no shipment 😉)
and ground the c tap
like this ?

 

[bequerel]

Usually you would lift the center tap via a voltage divider. You connect the center tap to the junction between the two resistors in the divider.

http://www.diyaudio.com/forums/tubes-valves/219669-12b4-linestage-woes.html

 

[JonSnell Electronic]

Usually you would lift the center tap via a voltage divider. You connect the center tap to the junction between the two resistors in the divider.

http://www.diyaudio.com/forums/tubes-valves/219669-12b4-linestage-woes.html

That would be a voltage doubler, reduced current will be available. Nothing wrong with the circuit as drawn.

 

[artosalo]

...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.

 

[DF96]

Hum should not be a problem in a line stage, so keep things simple. Ground the CT.

 

[michaelsamra]

This power -supply scheme would be ideal for the Cary SLP90

I posted but sadly there is no room for 10hy chokes unless you made it look awful in mounting them.

 

[paltal]

thanks

i'll start with the ct ground and proceed if necessary

another issue ... the cathode cap in the Design is 360uf and i'm having problems finding this value, any Suggestions ?

sorry michaelsamra, didn't quite understand

 

[artosalo]

Any value from 330 to 470 uF is ok for the cathode capacitor.

 

[paltal]

Any value from 330 to 470 uF is ok for the cathode capacitor.

thanks

 

[paltal]

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...

 

[DF96]

Little or no difference. Certainly no need to switch between them. Move your head a few inches in any listening room and you will get a much bigger shift in frequency response.

 

[paltal]

thanks
🙂 i get the picture

 

[Osvaldo de Banfield]

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.

 

[paltal]

hi
if i have a separate 6.3v winding for ez81 is it allso necessary to have the cathode and heater at the same potential?

 

[paltal]

a friend addvised to add fuses to each of the sec windings in addition of the one on the prim, is it a good idea ?
and if i do, for the HT ( 300-ct-300 ) winding need to put 2 fuses for each of the 300v ?
tnx