6.3V DC can you explain to me

[BOB42]

Good morning all
a question about the 6.3V DC heaters
on the attached diagram I use a configuration from this forum.
I can not decipher and therefore calculate the output voltage.
_using HT center tap as ground
_and creating a virtual ground via the two 470 Ohm resistors
can you explain to me how this circuit works?
thank you
BOB

 

[beatnik]

Have a look at this page, there is a section about DC heaters that you might find helpful

https://www.valvewizard.co.uk/heater.html

 

[abbey road d enfer]

Good morning all
a question about the 6.3V DC heaters
on the attached diagram I use a configuration from this forum.
I can not decipher and therefore calculate the output voltage.
_using HT center tap as ground
_and creating a virtual ground via the two 470 Ohm resistors
can you explain to me how this circuit works?
thank you
BOB

The 470r resistors are there to more or less balance the voltage both sides of ground (0V). Actually, it's the AC voltage that is balanced, so the DC voltage is not equally balanced.
But the important thing is the AC ripple is equally balanced, so it minimizes hum induction.
In order to get the best, the two resistors should be connected at the outputs, one between + and gnd, the other between - and gnd.
For the rest, the circuit is pretty much straightforward.

 

[moamps]

For the rest, the circuit is pretty much straightforward.

...except the rectifier is not connected properly.

 

[abbey road d enfer]

...except the rectifier is not connected properly.

Doh!
Straightforward does not mean it's correct...

 

[BOB42]

thanks to you two
what should be done for the diagram to be correct?
BOB

 

[abbey road d enfer]

thanks to you two
what should be done for the diagram to be correct?
BOB

Google bridge rectifier and compare.

 

[BOB42]

here is another version
is she correct?
BOB

 

[abbey road d enfer]

here is another version
is she correct?
BOB

Somewhat. You must decide if you ground the capacitors, in which case you end up with only a V+ and ground, or use the virtual ground resistors and you get a V+ and V-.

 

[BOB42]

Hello and thank you
here is a new diagram
I hope I understood
if this diagram is wrong can you make me a sketch to give me the right direction.
thank you
BOB

 

[abbey road d enfer]

Hello and thank you
here is a new diagram
I hope I understood
if this diagram is wrong can you make me a sketch to give me the right direction.
thank you
BOB

Wrong. The 470 ohm resistors must be from V+ and ground and from V- and ground.

 

[BOB42]

Thank you again for your help
attached new diagram
I hope I understood!
BOB

 

[abbey road d enfer]

Here we go...
Note that I offer no guarantee as to how it would perform, since it sepends on the actual transformer and what tubes there are to power.

 

[BOB42]

Thanks a lot
ground comes from HT center tape (300-0-300v)
transformer: Hammond 372 DX
the tubes: 1 EF86 tube and 2 E88CC tubes.
so 3 solutions for heating:
_ 6.3V AC
_ 0 /+6.3V
_ +3.15V /0 /-3.15V
what would be the best solution to limit the background noise?
BOB

 

[abbey road d enfer]

The last one.
An even better solution would be to use a potentiometer instead of the two resistors.

 

[beatnik]

That Hammond is overkill for a single Redd47 channel, it doesn't need such high currents, it's also physically large and expensive.

If mounted inside the same chassis as the preamp circuitry there will be quite some noise radiating from the transformer.
I would be more worried about this than AC or DC heaters and I prefer using a toroidal transformer to reduce noise.

Even with DC heaters 1A should be enough for the 6.3V winding and the HT winding probably needs no more than 40mA

I have used this transformer for similar preamp projects and it works well, you also get a spare 12V winding which could be used to power relays, led or other stuff

https://www.tube-town.net/ttstore/toroidal-47va.html

 

[abbey road d enfer]

Even with DC heaters 1A should be enough for the 6.3V winding

Simulation shows 1.8 Arms.
With the Hammond xfmr, the two 1 ohm resistors should be slightly increased (about 1.5r).
I agree that incorrect placement and orientation of the xfmr could result in killing all precautions taken with heater voltage filtering.

 

[beatnik]

Heater current is 200mA for the EF86 and 300mA for the E88CC

The op mentions above two E88CC tubes but in fact the REDD47 has only one, with the two triodes wired in parallel

I thought that if the heaters take 500mA AC, then with DC you would expect around 1A. And the 1.5A transformer I suggested should definitely be on the safe side.

 

[abbey road d enfer]

Heater current is 200mA for the EF86 and 300mA for the E88CC

Actually, in post #14 I had read it used two E88CC, but in fact it's only one. E88CC heater is rated at 365mA.
So the resistors should total 6ohms. 2.7 a,nd 3.3 should be OK.

I thought that if the heaters take 500mA AC, then with DC you would expect around 1A. And the 1.5A transformer I suggested should definitely be on the safe side.

Simulated RMS current is 1.2A. Of course need to be checked by experimentation.

 

[BOB42]

thank you both for your involvement
the potentiometer is a good idea
my project is the passive REDD47 + REDD EQ
the preamp has 3 lamps
1x EF 86 (6.3v 200mA)
2x E88CC (6.3V 300mA each)
because I added a buffer to resume level after passive EQ
the transformer is oversized because if the result suits me
I would do 2 channels.
on the 372 DX there is a 5V winding which allows me to use a GZ34 rectifier
on the HV winding there is a 50 VAC output
that I would like to use for phantom 48V
(it is true that one or 2 toroidal transformers would be less noisy)
initially a channel
tell me if my calculation of theoretical resistance is good
200mA+300mA+300mA=800mA
6.3Vac x 1.414= 8.9V -2V (diodes) = 6.9V-6.3V =0.6V/0.8A=0.75 R
the value seems wrong to me
I don't see or is it wrong?
BOB