I know this might sound strange, but I want to power tubes only to light up, I don't need to amplify any signal.
I have two cheap EL34, from the datasheet
Filament Voltage 6.3V
Filament Current 1.5A
A) I presume that in order to power both of them I need a transformer with 6.3V secondary and 3A in total. Am I correct?
B) Is AC ok? Or, do I need to provide DC voltage?
C) I have been told that doing this way the tubes won't last that much? Is this True? How long they can survive?
I know this is kind of strange, but I need this to make a terrible joke to a bunch of bad audio-friends.
I have two cheap EL34, from the datasheet
Filament Voltage 6.3V
Filament Current 1.5A
A) I presume that in order to power both of them I need a transformer with 6.3V secondary and 3A in total. Am I correct?
B) Is AC ok? Or, do I need to provide DC voltage?
C) I have been told that doing this way the tubes won't last that much? Is this True? How long they can survive?
I know this is kind of strange, but I need this to make a terrible joke to a bunch of bad audio-friends.
A) Correct. Or just get a switch mode supply that can be adjusted to 6.3V output. That will probably be cheaper.
B) AC or DC doesn't matter
C) If it's just for the light show it doesn't matter. You can use an NTC resistor to limit inrush current.
B) AC or DC doesn't matter
C) If it's just for the light show it doesn't matter. You can use an NTC resistor to limit inrush current.
Or you could run them in series at 12 volts and then only needs to be a 1.5A supply.
A few hours won't harm them at all either way.
Hope you audio pals do not read this forum...
A few hours won't harm them at all either way.
Hope you audio pals do not read this forum...
You are going to confuse them a lot, please use the cheapest smallest class D amp you find 😀
You can use a small transistor as switch and a mild high low current supply (100-200V) to make the tubes switch the main amp when the tubes fully warm, small signal relay can be switched with the cathode also without much effort the tube will only serve as a current source for this macgiver switch
You can use a small transistor as switch and a mild high low current supply (100-200V) to make the tubes switch the main amp when the tubes fully warm, small signal relay can be switched with the cathode also without much effort the tube will only serve as a current source for this macgiver switch
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Don't forget you are only using them for the glow, if it is a 6.3V heater you could just as easily run them under-powered with a serial resistor to keep the current down.
Simplest most straightforward is to get a 6.3V 3A transformer.
Maybe it´s easier to get the SMPS; if so, same thing.
Filaments will wear out in about 10.000 hours, is that long enough? 😛
AC or DC same thing, whatever you get.
I have done that joke countless times, specially when selling my Guitar amplifiers.
Some people NEED to see an orange glow and a glass bottle inside the amplifier 🙄
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Put a 6V 3A relay in series parallel with the heater filiments that closes the 120V main
You'll need a 12V 3A supply then.
You'll need a 12V 3A supply then.
In that case, an orange LED under the tube instead of using the heaters would work for the glow, and running the audio through the heater (it's equivalent to a few ohm resistor) would allow pulling the tube to stop the sound. Of course if you're using the heater, that tube will get HOT, so casually pulling it out might hurt.
Connect the cathode, anode, g1, 2 & 3 together and ground, that way the valve won't get trashed or work.
Andy.
Andy.
Somebody might get wise if you do that - having everything go dead when the tube is removed. You want to interrupt the audio - and leave the power stages and indicator lights running. Have the relay open up the DC supply to a preamp stage. Transformer and heat sinks still get warm with the power stage just idling.
If both tubes go out with one removed that might also be suspicious - that doesn’t normally happen. Use a small sense resistor in both to detect current, and a bit of logic to require current in both. Or do each channel separately (two relays, one to a preamp stage in each channel). That would be most like what happens if you take out a tube with it running.
If the two tubes are in parallel at 6V and a relay in series with each one 6V and each relay was applied to L&R channel in the preamp's signal path, say before the power amp?
This way you can make a chip amplifier looking like a tube amplifier. Your hifi friends will be amazed by its "tubey sound".
Next time go one step further: build a chip amplifier that really sounds like a tube amplifier.
Next time go one step further: build a chip amplifier that really sounds like a tube amplifier.
Those EL34 pentodes are going to "need" regulated screens (Need to LOOK like they are actually operating).
If you have +180V or more, use a series resistor from the B+ to an OD3 gas tube.
7mA will keep it out of the 5mA minimum.
The pretty purple glow will impress them.
Tell them how much better the amp sounds, now that you regulated the screens (not really running the screens).
If you have +180V or more, use a series resistor from the B+ to an OD3 gas tube.
7mA will keep it out of the 5mA minimum.
The pretty purple glow will impress them.
Tell them how much better the amp sounds, now that you regulated the screens (not really running the screens).
I wouldn’t use the relays in the signal path. Better to use them to switch DC power on to the preamp stage(s). Safe, doesn’t upset the main power amp and make loud thumps, and won’t add distortion from dirty contacts into the signal.
Want to REALLY make it look like it’s operating? Derive the 300 volt bias (and 180 volt screen) from a little Unregulated DC-DC upconverter, tied to the main power supply for the amp. The purple glow will modulate as the power supply sags when playing loud, just like a real class AB tube amp. Assuming of course your EL34’s fluoresce. Every pair I’ve ever had did.
I think someone sold an expensive DAC with a 12au7 tube.
Tube was only used for show. Anyone have a link?
Tube was only used for show. Anyone have a link?