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milen007 17th February 2009 01:36 AM

dc heater supply help
 
hi there

i need help on trying out dc heater supply for 6.3vdc 1.5A for the preamp i am running.

what kind of regulator to use? or use direct from rectifier and drop the voltage with the resistor to the required voltage?

it does need to float 25vdc above ground. where do i connect this floating connection?
to the ground of the heater supply or to the power transformer CT?

thanks in adv for the help

erwin

Richard Ellis 17th February 2009 02:05 AM

Erwin..We really do need a schematic so we can see what we all are working with.
For regulated DC for filiments, the 317 series regulators will do nicely....easy to configure, very clean DC.
As to the "floating 25 V"...I don't understand...nor where you need to connect to. This is where we need a schematic....
______________________________________Rick........ ....

milen007 17th February 2009 02:19 AM

hi guys

how bout secondary 5vac, rectify to around 7vdc. and use 0.7ohm 5watt resistors to drop the voltage to 6.3vdc. current is around 1A.

would this do? how big do you suggest the capacitor banks?

or any better option?

TIA.

Erwin

milen007 17th February 2009 02:27 AM

2 Attachment(s)
Hi Rick

here is the attached psu schematic.the floating is set by the 26K and 121K resistors. which five a nice 25vdc floating from ground to the heater supply. this floating dc is claimed can extend the life of the tube. since its not a problem then i just wired as suggested.

lm317... sounds good... will try this.

but will the floating dc affect the lm317 or the heater PT ?

erwin

HollowState 17th February 2009 02:40 AM

Yo Erwin,
A DC filament supply can be either regulated or unregulated. Regulated is better and requires less total parts for a quite DC output. However, if you need to elevate it 25 volts for heater/cathode reasons, you must keep it totally floating above ground or your supplys will be in conflict. Connect the 25 volts to the output of the DC supply were the filaments connect. Never before the regulator or rectifiers.

No, you cannot rectify 5 volts and expect to get 6 volts out under load. You must start with a higher voltage AC of at least 10 volts. This is because under load the voltage will drop down. And if you use a series pass device like a 317, you need at least a few volts extra so the device will see a differential which it need to operate. Capeesh?

milen007 17th February 2009 02:47 AM

Yo HollowState

thanks for the help. nice.

will hook one up and post back. i will just follow the 7v rules for the regulated supply. hence input of 15vdc and regulate it to 6.2vdc.

one more question. if the required 1A for AC current supply. is it still need 1A for DC current supply? or in DC it needs more?

i ask this question as i have try a chip regulated dc supply. though this psu rated for 3A. the 2n3055 runs extremely hot that i cant touch the heatsink (heatsink already double the required size). also the transformer runs very hot to touch that i have to disconnect them after less than an hour

erwin

HollowState 17th February 2009 03:08 AM

Quote:

Originally posted by milen007
one more question. if the required 1A for AC current supply. is it still need 1A for DC current supply? or in DC it needs more?

If you are asking if the tubes need more current under DC power, the answer is no, they require the same as for AC.

If things are running that hot, you are dissipating a lot of power. If your wiring is correct, then you need more heat sink still. And I just noticed something in your posted schematic. You show a capacitor across the filament winding. Don't do that! A capacitor represents a load across AC. This will strain and overheat your transformer. And you don't need one across the HV either.

milen007 17th February 2009 03:20 AM

Quote:

Originally posted by HollowState


If things are running that hot, you are dissipating a lot of power. If your wiring is correct, then you need more heat sink still. And I just noticed something in your posted schematic. You show a capacitor across the filament winding. Don't do that! A capacitor represents a load across AC. This will strain and overheat your transformer. And you don't need one across the HV either.

Yo HollowState

superb. will take that 4.7uf out and see what happen.

whats the reason why have to take out the 4.7uF caps before the filament in my case?

another questions, for regulated psu, can we put capacitor after the regulator? as i saw some people use caps after the regulator. is this the one cause the overheating of the PT?


:confused: :confused: :confused: :confused:

TIA

erwin

HollowState 17th February 2009 03:38 AM

Quote:

Originally posted by milen007
whats the reason why have to take out the 4.7uF caps before the filament in my case?

another questions, for regulated psu, can we put capacitor after the regulator? as i saw some people use caps after the regulator. is this the one cause the overheating of the PT?

Capacitors pass AC. It represents a resistor when connected to AC voltage. That's how it is shown on your diagram. There are no rectifiers so there is no DC to filter.

Normally there is a large capacitor before the regulator. After the regulator use only a small value capacitor to quite any possible noise if needed.

(I'm turning in for the night)

Victor

Vlauga 17th February 2009 09:03 AM

Hi, milen007!

For what purpose it is necessary for you to DC supply for filaments of tubes? Your preamplifier has tubes with direct heating?

If is not present, then your first scheme will unconditionally clean an AC hum from heating of tubes.

In any case, at DC supply of filament of tubes to associate ~ +25V it is possible to any wire of a feed of filament (only for one!)

BW, VU


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