Greenie

Transformer for the C12 build
« on: March 20, 2020, 10:48:48 AM »
Hi.  I just wondered what transformer is needed in the PSU for the C12 build?
« Last Edit: March 20, 2020, 11:11:00 AM by Greenie »


RuudNL

Re: Transformer for the C12 build
« Reply #1 on: March 20, 2020, 12:33:28 PM »
In the attachment you will find the (original) N12A schematic.
As you can see, they used 22 Volts for the filament and 155 Volts for the +HT.
Both voltages are on the high side, IMHO.
For the filament you want an output of 5 to 6.3 Volts. Nowadays we would use a LM317 for this.
Because after rectification and smoothing the DC voltage is higher than the AC voltage from the transformer, I would go for an AC voltage of 9 to 12 Volts.
The load of the +HT is very low, so a lot of energy is dissipated in the dropper resistors.
I think the best thing you can do is find a commercially available transformer, such as 2 x 6.3 V (in series) and 1 x 120 V (AC).
There is a solution for every problem!

http://www.vansteenisaudio.nl

Greenie

Re: Transformer for the C12 build
« Reply #2 on: March 21, 2020, 12:59:06 PM »
Thanks for the answer.  I have 240v in the outlet, does that change anything?

RuudNL

Re: Transformer for the C12 build
« Reply #3 on: March 21, 2020, 01:02:10 PM »
No, because the only thing you are interested in are the secundary voltages.
(No matter if your mains voltage is 110 or 240 Volts!)
In your case you will need a transformer with a primary voltage of 240 volts.  Or two 120 volts windings in series.
« Last Edit: March 21, 2020, 01:16:08 PM by RuudNL »
There is a solution for every problem!

http://www.vansteenisaudio.nl

TLRT

Re: Transformer for the C12 build
« Reply #4 on: March 22, 2020, 06:47:22 PM »
The vintage c12 has selenium rectifiers,so the dc after rectification is almost the same(no multiplier with 1,41 as with the silicone zener diodes),the modern psu's with lm317 regulated heaters can be used with 9,5V and 200V secondaries. I have custom made trafos with that voltages if you need one. If you dont use LM317 then 20V/200V is recommended.

RuudNL

Re: Transformer for the C12 build
« Reply #5 on: March 23, 2020, 02:28:47 PM »
200 Volts AC will give rectified and smoothed ~ 280 Volts DC. (The load is minimal.)
A C12 needs a +HT of 120 Volts. So that is a lot of power to dissipate!
(In fact you waste more power than you use...)
There is a solution for every problem!

http://www.vansteenisaudio.nl

TLRT

Re: Transformer for the C12 build
« Reply #6 on: March 24, 2020, 06:03:37 PM »
200 Volts AC will give rectified and smoothed ~ 280 Volts DC. (The load is minimal.)
A C12 needs a +HT of 120 Volts. So that is a lot of power to dissipate!
(In fact you waste more power than you use...)

True, but with a 200V secondary you can use the trafo for all builds(even ef86 or vf14/u47)


 

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