I use a 1mA analog meter movement.
Example:
RK = 1k Ohm (Self Bias Resistor)
1mA meter movement (you could also use one of those real small digital meters)
100k Ohm resistor in series with the 1mA meter movement (that combination connected across the 1k self bias resistor)
Tube self bias warm = 60mA (60V bias across the 1k Ohm resistor).
0.6mA through the meter, the needle shows 0.6mA.
Actual Cathode current = 60mA + 0.6mA = 60.6mA (who cares about 1% extra cathode current?).
When you turn on the amp, you can easily see the complete warm-up, as the needle slowly goes from 0 to 0.6mA.
And, I can see if the tube starts going into thermal run-away, or if the tube is wearing out.
That is just my simple way to do it.
Question: When is a tube warmed up?
When it is at 95% of final current, or 99% of final current?
Or After 5 minutes when the plate temperature is at 95% of its final temperature?
Or . . . you pick the criteria
Worry, Worry, Worry
Is this a recording studio doing an important recording session?
Is it a time to show off your system to the local vacuum tube club?
Or is it just a relaxing music listening session with your spouse?
Example:
RK = 1k Ohm (Self Bias Resistor)
1mA meter movement (you could also use one of those real small digital meters)
100k Ohm resistor in series with the 1mA meter movement (that combination connected across the 1k self bias resistor)
Tube self bias warm = 60mA (60V bias across the 1k Ohm resistor).
0.6mA through the meter, the needle shows 0.6mA.
Actual Cathode current = 60mA + 0.6mA = 60.6mA (who cares about 1% extra cathode current?).
When you turn on the amp, you can easily see the complete warm-up, as the needle slowly goes from 0 to 0.6mA.
And, I can see if the tube starts going into thermal run-away, or if the tube is wearing out.
That is just my simple way to do it.
Question: When is a tube warmed up?
When it is at 95% of final current, or 99% of final current?
Or After 5 minutes when the plate temperature is at 95% of its final temperature?
Or . . . you pick the criteria
Worry, Worry, Worry
Is this a recording studio doing an important recording session?
Is it a time to show off your system to the local vacuum tube club?
Or is it just a relaxing music listening session with your spouse?
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The assumption that a tube is "warmed up" when the cathode is at 100% (or nearly so) emission, and the tube is outputting audio from the plate at full volume. The idea is to let newbies know that the amplifier is not defective just because it makes them wait up to 15 seconds before the volume goes up to 100%. This is especially true when most people these days are ordinarily accustomed to the instant start-up associated with solid state electronics.
In order to better illustrate that, let me give you a hypothetical situation:
I want to avoid any semiconductor devices at all costs--this includes LED's. No silicon, germanium or selenium whatsoever. Hence my design only works with cathode-biased output stages. Unless you can recommend an incandescent or neon indicator than I could use instead of an LED, your idea is useless to me.
Very interesting. However, this circuit would suggest that the neon indicator is operating off of DC voltage, and the only neon indicators I can find on the Mouser website are AC rated. Will the circuit still work?
In any case, my initial thought with the relay circuit was for the light to suddenly turn off (or on), rather than gradually "ramp up" in brightness, which is what this circuit also suggests.
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I was able to find a 1.5V bulb at Mouser, but unfortunately it draws 0.075A of current--considerably more than the cathode current of a preamp tube (0.001A). Remember that in a series circuit all points within that circuit must have equal current draw (at least that's what I've heard).
I also wanted the turning on/off of the bulb to have sudden instead of gradual action. IOW, I want it to "suddenly" turn on or off instead of gradually increasing in brightness.
How about a simple timer? Use an RC time constant to have a tube conduct and light a neon lamp. They run fine from dc but only one electrode will light.
Seriously?
Have you considered simply mentioning that tubes take 20 or 30 seconds to warm up? Why not just include such a statement in the auction description and also in a list of basic instructions that you ship with the amp? No additional circuitry necessary.
I figure that anyone who can't simply remember such basic instructions should stick with SS. If they're really that clueless, how can you even be sure they can safely plug the amp into an AC outlet?
If you're really that paranoid about problems that might arise as the result of selling an amp, you probably shouldn't be selling amps.
Frankly, I don't see how this would be a serious concern since, even if the sound doesn't come up right away, the amp will not be harmed. This is a solution in search of a problem.
A more serious concern - one that could actually cause damage - would be running the amp without speakers or some load connected. Tube newbies may have done that previously with SS gear.
Sorry, I probably shouldn't have mentioned that. Now you probably won't be able to sleep at night.
And, while SS audio gear may start up immediately, not everything we use does.
How long do you have to wait for your computer to boot up? Or your Wi-Fi cable modem? Or to get heat from the heater in your car after you first start it on a cold winter morning? How long does it take for your car's AC to blow cold if it's been parked in the sun for a few hours in summer? How long does it take to preheat your oven to the correct temperature? All of these take longer than it takes for a tube amp to warm up.
But, hey, this is DIY Audio. I'm sure you'll think of a solution, even if the problem is non-existent. Extra points if it's complicated and expensive, of course.
What a hoot.
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Neon bulb
Yes, in this implementation the neon bulb is working off of DC. But neon bulbs work off either AC or DC, so long as you meet the applicable turn-on voltage and "sustain" voltage (which is much lower than the turn-on voltage). Your typical NE-2 will work on either AC or DC. Here is an manufacturerʻs explanation of neon bulbs: Neon Lamps, Neon Indicator Lamps | ILT.
Yes, in this implementation the neon bulb is working off of DC. But neon bulbs work off either AC or DC, so long as you meet the applicable turn-on voltage and "sustain" voltage (which is much lower than the turn-on voltage). Your typical NE-2 will work on either AC or DC. Here is an manufacturerʻs explanation of neon bulbs: Neon Lamps, Neon Indicator Lamps | ILT.
RIDICULOUS made up "situation" just to "justify" yor cheesy "relay in parallel with cathode resistor" idea.
Of course you have never actually built it.
Remember to tell buyer your amp is only allowed to play back tapes recorded live using Neumann Tube mikes into a Roberts 1957 vintage Tube tape recorder, using same for playback, or Vinyl recorded pre-1958,or it will void warranty.
Always the polite guy, finding diplomatic ways to say things.
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That's 20th century thinking. For at least the last 5 years NOTHING boots-up instantly. My PC takes 75 seconds to begin to take orders. My cellphone takes even longer. (True, I don't turn either off as often as I would a tube.) Even my battery electric saw and lawnmower do NOT start when I pull the trigger, there is a perceptable self-test delay.
The truly "period" boot indicator IS an electric clock unit. Of course I can't find one when I need one, but this type motion:
tells the kiddies "wait!"
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This worrying over some goofy "newbe" stuff and a lousy 15 seconds warmup is dumb, and overthinking things.
If a person is that upset over waiting 15 seconds, they've got a mental problem.
There are drugs and doctors that help that kinda stuff.
If a person is that upset over waiting 15 seconds, they've got a mental problem.
There are drugs and doctors that help that kinda stuff.
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I think a warm up indicator is cool, regardless if its really necessary for those who might be confused about why the music doesn't play right away, its DIY. Figuring out how to do a threshold indicator in general without affecting the circuit is a worthy exercise in itself, for many things other than tube readiness. Who knows why some would rather write a long post on its ridiculousness rather than post their voltage indicator solutions. I think its an interesting problem.
As I have suggested indirectly, any "problem" was solved decades ago by the approach of using the neon indicator at the last stage of PS filtering. Why is it that a neon lamp and current limiting resistor is not acceptable; it certainly is the most inexpensive and least likely to fail solution. I thought that the purpose of engineering was to find the simplest and most elegant solution?
I didn't have anything against the neon bulb method. My initial thought that tying it to the rise in cathode voltage while a tube was warming up would be an accurate indication of the tubes being ready to play audio. At first I was skeptical to the neon-bulb method as it implies the need to "synchronize the RC" filter with the warm up cycle, but I am willing to try the neon bulb method...if I can find an appropriate SPICE model for one...
The amplifier is not going to operate until the last RC power supply section is charged up (assuming one is using an indirectly heated tube rectifier). So there is no real need for calculating the time it takes for the RC section to charge up to the striker voltage of the neon bulb. However if one is using a solid state B+ rectification system, then I would agree that the neon bulb approach is not going to work effectively unless one calculates the charge-up time for a special RC section that feeds only the neon bulb. Iʻm pretty sure that, in that case, the time constant is figured out using the standard RC equation.
Yes, I in the amp I am in the process of designing now, a simple single-ended mono phonograph amplifier intended to be paired with an old Garrard record changer that came out of an old Harman Kardon solid-state tabletop FM receiver that I junked, I intend to use a 6CA4 rectifier tube (indirectly heated, separate filament and cathode pins on the socket). I think I have an idea of what it would potentially look like, adapted from the earlier Scott 200 schematic.
You will note that I am still using a relay to control the neon indicator, so that the bulb has sudden illumination action rather than a gradual increase in brightness.
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