I'm trying to use the PSUD2 to design a DC filament supply for 2 6SN7 tubes.
I assume you use a resistive load because its a heater, but where do I find the value of the resistance? I also assume that this resistance changes as the tube heats up.
I've never used DC for heaters, so I thought I'd give it a try.
Are the heaters still wired in parallel as AC heaters are?
Thanks in advance.
Glenn
I assume you use a resistive load because its a heater, but where do I find the value of the resistance? I also assume that this resistance changes as the tube heats up.
I've never used DC for heaters, so I thought I'd give it a try.
Are the heaters still wired in parallel as AC heaters are?
Thanks in advance.
Glenn
load resistance for PSU designer
Use a resistive load of 6.3 V / .6 A = 10.5 ohms. This is the hot value, valid after 15 or 20 seconds. Yes the initial value is lower, and your simulation for the first 15 seconds will be inaccurate, but so what ? I think you are really only interested in the steady state DC voltage and ripple.
As for series or parallel, that depends on wether you have 12.6 volts ( use series ) or 6.3 volts ( use parallel ) available.
Use a resistive load of 6.3 V / .6 A = 10.5 ohms. This is the hot value, valid after 15 or 20 seconds. Yes the initial value is lower, and your simulation for the first 15 seconds will be inaccurate, but so what ? I think you are really only interested in the steady state DC voltage and ripple.
As for series or parallel, that depends on wether you have 12.6 volts ( use series ) or 6.3 volts ( use parallel ) available.
Yes, I've never had a need for DC heaters in the past, but I like to have a "plan B" if needed. It's also another thing I'd like to experiment with just because I've never done it.
This is for a line level 2 tube 6SN7 preamp, so the wiring is pretty simple compared to other jobs I've done.
I never thought about the voltage rise if a tube is removed, good point. Of course I would never do such a thing
Here's my layout so far:
6SN7 preamp
Glenn
This is for a line level 2 tube 6SN7 preamp, so the wiring is pretty simple compared to other jobs I've done.
I never thought about the voltage rise if a tube is removed, good point. Of course I would never do such a thing
Here's my layout so far:
6SN7 preamp
Glenn
dhaen said:
I had a question on this. I'm using a PT without a CT for the 6.3v for the first time. The schematic calls for using (2) 50 ohm resistors for the "artificial center tap". Is there any specific reason for using theses values for the resistors? The main reason is that 51 ohms is a common value. I know they do make 50 ohm rheostats for hum balance, but I not to use one.
Thank you.
Glenn
Glenn,
50 ohms is just a rough value. I've used 100 ohm, and various other values. It's just got to be low enough to tie hum pickup to ground, without dissapating too much heat.
Doing this, or grounding a centre tap, makes the heater wiring into a balanced feed which radiates next to no common mode hum, and the twisting cancels differential hum. Magic..
50 ohms is just a rough value. I've used 100 ohm, and various other values. It's just got to be low enough to tie hum pickup to ground, without dissapating too much heat.
Doing this, or grounding a centre tap, makes the heater wiring into a balanced feed which radiates next to no common mode hum, and the twisting cancels differential hum. Magic..
100 ohm is the universal standard in thousands of guitar amps f they don't have center taps. It is also customary in guit fiddle amps to tie the junction of those resistors to the output tube cathode bias resistors for a slightly elevated reference... although I usually like to go to about 25% of the supply voltage on my reference from a voltage divider from the B+, decoupled with a small capacitor. Never had any hum problems that way. i have used DC in the past and gotten low level buzz, like you fellows pointed out, so I do all AC now.
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