Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: joesatch on May 03, 2022, 07:59:07 am
-
Can i run these two 6.3vac secondaries in series to get 12.6vac? Will this cause a house fire?
-
you'll have to make sure to wire in phase otherwise you'll add 6.3v and 6.3v and end up with 0v
do you have a link to that transformer? that would work as replacement to a 217vac/12.6vac toroid i've used that's no longer available
-
do you have a link to that transformer? that would work as replacement to a 217vac/12.6vac toroid i've used that's no longer available
like this? What is the result in volts, amps?
https://www.antekinc.com/as-05t200-50va-200v-transformer/ (https://www.antekinc.com/as-05t200-50va-200v-transformer/)
-
Yes, like ^that^ 12.6V 2A
-
if i ran the 12.6v through a FWB what would be the DC voltage?
-
guessing around 17-18v un-loaded out of the bridge
-
for 12vdc heaters would you use dropping resistors after the fwb or incorporate a voltage regulator to get it to 12vdc?
-
when I build a PS for some need, I decide if I need regulated or just close.
I put FIL in the just close box
so I put a CRC after the bridge, then calculate the current load for my need.
then I calculate a "dummy load" resistor to simulate my need. wire it up, and make measurements.
from there I decide if it's close enough, needs tweaking, or back to the drawing board.
-
voltage regulator it is!
:l2:
https://www.mouser.com/ProductDetail/STMicroelectronics/L7812CV?qs=5Uvc6lfWVJzVGZQZmBynyg%3D%3D (https://www.mouser.com/ProductDetail/STMicroelectronics/L7812CV?qs=5Uvc6lfWVJzVGZQZmBynyg%3D%3D)
-
voltage regulator it is!
Output current up to 1.5 A
Will it be enough?
-
ya i'm powering (3) 12ax7
-
OR....
Voltage doubler on one winding....
-
Hi joesatch,
I have done DC supplies for ECC83/12AX7 on a number of occasions (in preamps). See attached pix.
I suggest an LM7812T with a diode on GRD terminal to give you 12.55V DC nominal.
You said 3 off 12AX7 requiring approx 150mA per tube 12.5V DC, so 3 tubes would require a little less than 500mA.
Shooter correctly approximated 17V to 18V DC from your 12.6V AC transformer taps.
The main reason I'm pitching in is that your LM7812T may need a heatsink, as say 17.5V -12.5V gives around 5V at approx 500mA comes in just under 2.5W. Shouldn't be a big problem, doesn't have to be big, but you need to secure it in the chassis.
I suggest 2.5W is quite warm and gets worse if you increase number of tubes.
Regards
Mirek