I don't know much about tubes but it seems reasonable to assume that the filament is not supposed to be fed by a constant current. If the filament is 5 V I think you supply the 5 V and then the current draw is simply around the 1.5 A changing a little after heating up. I donät think it is necessary to limit the current. Also you can not set the voltage and the current at the same time for this type load as it will either need to use the full voltage when current draw at 5 V is lower than 1.5 A (thus using less than the stated) and less than full voltage if current draw at 5 V is higher than 1.5 A (and thus woule be using more than 1.5 A if voltage set to 5 V).
I suggest using 5 V supply capable of at least 2 A and then everything should be fine. Please however trust other sources on tube supplies before me...
If however you need to regulate the current then I am sure the app notes/datasheet describe that. Essentially you connect a resistor on the output of the reg and then Vadj directly to the output end of that resistor. The current regulated would be approximately Vref/R1 as the reg tries to maintain 1.25 V between those pins. So your current would be 1.25/R1 which for 1.5 A would mean (solved for R1) 1.25/1.5=0.83 Ohms.
I suggest using 5 V supply capable of at least 2 A and then everything should be fine. Please however trust other sources on tube supplies before me...
If however you need to regulate the current then I am sure the app notes/datasheet describe that. Essentially you connect a resistor on the output of the reg and then Vadj directly to the output end of that resistor. The current regulated would be approximately Vref/R1 as the reg tries to maintain 1.25 V between those pins. So your current would be 1.25/R1 which for 1.5 A would mean (solved for R1) 1.25/1.5=0.83 Ohms.
Thanks for the replies!
My plan is to use a voltage regulator first LM350, then add the LM317 stage...which would use a 0,83R resistor...1,25/1,5 from Jim's link see below. (for a 1,5A current supply)
"One three pin adjustable voltage regulator and one resistor are all that is needed to make a current source, a high current one at that. The desired current is set by the value of the resistor, which is found by dividing the base voltage (1.25 volts usually) by the desired current. For example, if we want 900 mA, we use a 1.39 resistor, as 1.39 = 1.25 / 0.9 ."
Regards,
Bas
My plan is to use a voltage regulator first LM350, then add the LM317 stage...which would use a 0,83R resistor...1,25/1,5 from Jim's link see below. (for a 1,5A current supply)
"One three pin adjustable voltage regulator and one resistor are all that is needed to make a current source, a high current one at that. The desired current is set by the value of the resistor, which is found by dividing the base voltage (1.25 volts usually) by the desired current. For example, if we want 900 mA, we use a 1.39 resistor, as 1.39 = 1.25 / 0.9 ."
Regards,
Bas
I reg
Bas,
A tube with a heater specified in volts (there are of course also tubes with a heater specified in current) should see the recommended voltage for optimum performance, e.g. 6.3V for the E-types.
What you want to do I think is limit the current at start-up to prolong heater (& tube) life, but give them the recommended voltage after that.
So what I would recommend is a regulated 6.3V voltage regulator with a current limit set to say 120% or 130% of the expected current comsumption.
Of course, it gets more complicated with several heaters on the same regulator.
Jan Didden
Bas,
A tube with a heater specified in volts (there are of course also tubes with a heater specified in current) should see the recommended voltage for optimum performance, e.g. 6.3V for the E-types.
What you want to do I think is limit the current at start-up to prolong heater (& tube) life, but give them the recommended voltage after that.
So what I would recommend is a regulated 6.3V voltage regulator with a current limit set to say 120% or 130% of the expected current comsumption.
Of course, it gets more complicated with several heaters on the same regulator.
Jan Didden
I got some prints from a fellow diy tube builder (Doede Douma). That have been made for the attached schematic. And I thought it was a good idea to use them both for a 300b amp I'm gonna build one day.
So initially I though just set the voltage reg to 5v and the current reg to 1,5A.. But Jim's suggestion sounded logical..The current reg needs a higher voltage because it will also drop voltage??
So initially I though just set the voltage reg to 5v and the current reg to 1,5A.. But Jim's suggestion sounded logical..The current reg needs a higher voltage because it will also drop voltage??
Attachments
Bas,
A few words about the LM317:
Making sure that there is sufficient input voltage is essential for all regulators in all modes, although you may have to allow extra for the voltage drop across the output resistor in current mode. I aim for 4 to 5 volts. Remember the regulator needs working volts, even in the "trough"of the input ripple.
The National datasheet says it all:
http://www.national.com/ds/LM/LM117.pdf
Also, consider the wattage of the variable resistor on the output of the current mode supply. If the pot is turned near to the max current end, there is considerable current flowing through it, and only a small amount of track to dissapate the power.
Cheers,
A few words about the LM317:
Making sure that there is sufficient input voltage is essential for all regulators in all modes, although you may have to allow extra for the voltage drop across the output resistor in current mode. I aim for 4 to 5 volts. Remember the regulator needs working volts, even in the "trough"of the input ripple.
The National datasheet says it all:
http://www.national.com/ds/LM/LM117.pdf
Also, consider the wattage of the variable resistor on the output of the current mode supply. If the pot is turned near to the max current end, there is considerable current flowing through it, and only a small amount of track to dissapate the power.
Cheers,
Hi Bas,
Use Duncan's PSU program to simulate.
It'll depend on your smoothing to a great extent.
I use DC for the drivers through CRC smoothing, with a resistor in the top and bottom rails. This gets rid of the slow common mode crap. The fast stuff is trapped by a common mode choke.
The 845's use AC at present, and the hum is only just good enough. I'm considering DC.
I considered HF heating, but decided against it because of possible IMD.
Cheers,
Use Duncan's PSU program to simulate.
It'll depend on your smoothing to a great extent.
I use DC for the drivers through CRC smoothing, with a resistor in the top and bottom rails. This gets rid of the slow common mode crap. The fast stuff is trapped by a common mode choke.
The 845's use AC at present, and the hum is only just good enough. I'm considering DC.
I considered HF heating, but decided against it because of possible IMD.
Cheers,
Why am I doing this...well...because....i can!!
Just kidding.
Know the old discussion about AC/DC on the filaments? Sure you do.
Apparently one of the better sounding DC solutions is current regulation. (Jeez where have you guys been the last couple of years) ;-)
Doede Douma of www.dddac.de fame has made a couple of boards..so he must be thinking of doing the same thing. He has these boards where you have voltage reg and current reg.
(Actually just checked a new page (for the first time) of his out where he says a couple of things about it and actually has the formula that I originally posted for) Duh..RTFM BAS
I want to go a step further and do some filtering after that... as John is doing...ie resistors for the slow junk and common mode chokes for the fast nasties.
Thereby creating a sort of deluxe DC filament supply hopefully able to compete with AC.
What do you guys think...Personally I am baffled by the fact that most people agree AC on filaments sounds better...and the EE type DIY'ers have not designed some ultra good sounding DC supply, with boards and the works. There must be a good market for that.
Cheers,
Bas
Just kidding.
Know the old discussion about AC/DC on the filaments? Sure you do.
Apparently one of the better sounding DC solutions is current regulation. (Jeez where have you guys been the last couple of years) ;-)
Doede Douma of www.dddac.de fame has made a couple of boards..so he must be thinking of doing the same thing. He has these boards where you have voltage reg and current reg.
(Actually just checked a new page (for the first time) of his out where he says a couple of things about it and actually has the formula that I originally posted for) Duh..RTFM BAS
I want to go a step further and do some filtering after that... as John is doing...ie resistors for the slow junk and common mode chokes for the fast nasties.
Thereby creating a sort of deluxe DC filament supply hopefully able to compete with AC.
What do you guys think...Personally I am baffled by the fact that most people agree AC on filaments sounds better...and the EE type DIY'ers have not designed some ultra good sounding DC supply, with boards and the works. There must be a good market for that.
Cheers,
Bas
Baz,
My gut instict is that regulation (of either type) is only useful for controlling emission. And that the variations in my mains supply: about 0 to -3%, do not warrant it.
Indeed, if I were to incorporate regulation, I would need to include further noise filtering, as regualtors can be "noisy buggers".
Regarding current vs. voltage regulation:
Most of the valves we use are specified for either:
1) Fixed voltage source
or,
2) Fixed current source
The fixed current source types are mainly TV and AC/DC radio types.
I am unconvinced that running a valve contary to it's specification will reap benefits.
So there..
The few "dual specified" types that come to mind are the ECC8X series, but even they have different pins used for each.
Cheers,
Having just read this through, it sounds really bitchy; it's not meant that way.
My gut instict is that regulation (of either type) is only useful for controlling emission. And that the variations in my mains supply: about 0 to -3%, do not warrant it.
Indeed, if I were to incorporate regulation, I would need to include further noise filtering, as regualtors can be "noisy buggers".
Regarding current vs. voltage regulation:
Most of the valves we use are specified for either:
1) Fixed voltage source
or,
2) Fixed current source
The fixed current source types are mainly TV and AC/DC radio types.
I am unconvinced that running a valve contary to it's specification will reap benefits.
So there..
The few "dual specified" types that come to mind are the ECC8X series, but even they have different pins used for each.
Cheers,
Having just read this through, it sounds really bitchy; it's not meant that way.
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