So while musing about attenuators, I wondered if the output of a low wattage SE amplifier could be rectified and power a dc motor or chip amp or anything ?
Not worrying about getting the perfect attenuator / re-amp or solving any specific problem.
Rather wondering how it would be done and the likelihood of any useful results.
Hey maybe I want to put wheels on my 50s mantle radio and have it drive around the room based on what music is playing.
Ok Maybe not but it might make for some interesting discussion.
Would they be enough power to move it at all or do we need to go to the shop to get more extension cords.
Doesn’t have to be too deep a technical discussion, but yes design a working solution by all means if you like.
Motor was just a thought bubble. However I would like to keep the discussion related to lower power applications.
Not worrying about getting the perfect attenuator / re-amp or solving any specific problem.
Rather wondering how it would be done and the likelihood of any useful results.
Hey maybe I want to put wheels on my 50s mantle radio and have it drive around the room based on what music is playing.
Ok Maybe not but it might make for some interesting discussion.
Would they be enough power to move it at all or do we need to go to the shop to get more extension cords.
Doesn’t have to be too deep a technical discussion, but yes design a working solution by all means if you like.
Motor was just a thought bubble. However I would like to keep the discussion related to lower power applications.
That's crazy nutter!
Yes, low wattage SE amp can easily be rectified and power something. But it will be low wattage. You would have to drive the amp to full power all the time, to produce just few watts. With normal music, it would not be enough to power anything. Perhaps blinking light.
Yes, low wattage SE amp can easily be rectified and power something. But it will be low wattage. You would have to drive the amp to full power all the time, to produce just few watts. With normal music, it would not be enough to power anything. Perhaps blinking light.
Yes no self powered slot car mantle radio dam it🤪
I guess that would be enough to power a headphone amplifier. The source signal could be a sample / line out from the amp itself.
If you have a 2.1 system you could use 3 moderate power lightbulbs with different colours as anode load instead of a transformer and have a disco light 🙂
Headphone amplifier for sure, just load the amp with resistor to make output trafo happy.
No rectification!
Short answer as above - yes. Typically they're called hybrid (meaning tube and solid-state amplification).
I'm working on a hybrid 12BH7A-NPN circlotron. It class A for both sections, so it draws full current all the time. Being a circlotron it has two amps per channel (+ and - as there's no grounded output). However being a hybrid circlotron each amp has a power supply for the tube and one for the solid state, so a headphone amp has 9 power supplies (with 9 transformer secondaries) - it gets complicated and crazy!
So the use of an amplifier in power regulation is a regular thing - the opamp is a differential amplifier which is used to control the voltage managed by a solid state device to control the current. You could make a tube based opamp to replace the solid state opamp. Typically BJTs or MOSFETs are used to manage the current but it's also possible to utilise tubes (such as the humble 6AS7 which was designed originally as a series pass device for this precise purpose). The issue is having a tube control the main current flow limits the current it can regulate. You also need to warm the heaters up, so it takes a while before either (a) a tube series device starts conduction and (b) a tube opamp controlling it to heat up and conduct. So those tubes probably need AC heaters for simplicity.
You could even make a tube SMPS. although the power would be very low unless you used those large kilovolt tubes.
I'm working on a hybrid 12BH7A-NPN circlotron. It class A for both sections, so it draws full current all the time. Being a circlotron it has two amps per channel (+ and - as there's no grounded output). However being a hybrid circlotron each amp has a power supply for the tube and one for the solid state, so a headphone amp has 9 power supplies (with 9 transformer secondaries) - it gets complicated and crazy!
So the use of an amplifier in power regulation is a regular thing - the opamp is a differential amplifier which is used to control the voltage managed by a solid state device to control the current. You could make a tube based opamp to replace the solid state opamp. Typically BJTs or MOSFETs are used to manage the current but it's also possible to utilise tubes (such as the humble 6AS7 which was designed originally as a series pass device for this precise purpose). The issue is having a tube control the main current flow limits the current it can regulate. You also need to warm the heaters up, so it takes a while before either (a) a tube series device starts conduction and (b) a tube opamp controlling it to heat up and conduct. So those tubes probably need AC heaters for simplicity.
You could even make a tube SMPS. although the power would be very low unless you used those large kilovolt tubes.
Last edited:
Nixie tube display - another place tubes can be used 🙂
The more complex would be tube oscilloscopes, signal generators (let's ignore microwaves and X-ray machines), DSD512 capable DACs (MarcelG).
Back in the 60s, EMI used a tube power amp to drive the synchronous capstan motor in a tape recorder. By feeding a variable frequency through the amp they could vary the speed of the tape recorder. The original varispeed.
Cheers
Ian
Cheers
Ian
I'm certain you could have your radio drive around using power from the audio output, small DC motors can be purchased that run on less than 200 milliwatts, by using some low friction gearing such that the top speed was maybe 100mm per hour it should work fine. Remember Archimedes said "Give me a lever long enough and a fulcrum on which to place it, and I shall move the world". Another method would be to very slowly charge a 18650 battery then run at high speed for a while.
Sylvia Massy does stuff like this all the time
edit: the signal path is amp -> lightbulb -> speaker
edit: the signal path is amp -> lightbulb -> speaker
Here are 20 6AQ5s in a stacked PP setup. !00 Watts.
Ran a synchronous motor, speed varied as the input frequency was varied.
PS was plus & minus 300V. The top set of AQ5s is bootstrapped.
FB is current so that voltage varies with frequency.
Built this one circa 1960, its still here on the shelf WO the AQ5s. 😀
Ran a synchronous motor, speed varied as the input frequency was varied.
PS was plus & minus 300V. The top set of AQ5s is bootstrapped.
FB is current so that voltage varies with frequency.
Built this one circa 1960, its still here on the shelf WO the AQ5s. 😀
Attachments
1. It can be a plate modulator to power RF generator. Let others enjoy (or hate) the stuff that you are listening.
2. It can drive color light display to make automatic color music. It was a fad in mid-60s.
2. It can drive color light display to make automatic color music. It was a fad in mid-60s.
Use it for the vertical deflection amplifier of a DIY tube TV set. Assuming of course you have an old VHS or other NTSC video source available.
Personally I’d probably end up using it as an AM modulator. My old disco light show is all solid state.
Personally I’d probably end up using it as an AM modulator. My old disco light show is all solid state.
You can make the case that a tube amp is an audio amp because we say so. The amp itself has no clue, it just amplifies the input signal and serves it up to a load within its capabilities.
So, yes, the answer is yes, within its capabilities.
Jan
So, yes, the answer is yes, within its capabilities.
Jan
As mentioned the output of a tube or solid state amp could be used to power just about anything within its power rating. You are not going to run a 100 watt motor, light or anything on a 10 watt amp. You can run a low wattage motor on the output of a tube or solid state amp with the proper matching transformer. Back in the late 60's I powered my Garrard turntable from the output of an old Stromberg Carlson PA amp that feed the secondary of a good sized 115 to 12 volt transformer with the turntable connected to the primary winding. The amplifier was driven from an old sine wave audio signal generator. The frequency of the generator controlled the pitch of the record being played and the amplitude was adjusted to provide about 115 volts to the turntable. This was done so that I could learn fast guitar riffs. Later I got a tape recorder that had two speeds which made this rig obsolete and it was dismantled. I'm thinking of making something similar to add pitch bend to a Hammond M-3 tone wheel organ, but if I build it, it will use a solid state class D amp.
When I started in the cal lab at Motorola I saw this monster vacuum tube audio amp that fed a large shaker table. The amp drove the table which shook mobile radios to destruction with variable frequency sine, square or triangle waves. G-force sensors were used to determine peak acceleration. This was all scrapped in the mid 80's and replaced with a "modern" solid state unit that had preprogrammed profiles and g-forces. The programs were recorded in actual real world scenarios. My favorite was "military Jeep" om about 5G's. It could shake the life out of anything made out of plastic.
When I started in the cal lab at Motorola I saw this monster vacuum tube audio amp that fed a large shaker table. The amp drove the table which shook mobile radios to destruction with variable frequency sine, square or triangle waves. G-force sensors were used to determine peak acceleration. This was all scrapped in the mid 80's and replaced with a "modern" solid state unit that had preprogrammed profiles and g-forces. The programs were recorded in actual real world scenarios. My favorite was "military Jeep" om about 5G's. It could shake the life out of anything made out of plastic.
The vertical deflection section of an old tube TV is actually a class A SE optimized for a single frequency around 50 or 60 Hz. They work very well as audio amps too. I exploited this fact as a kid making guitar amps in the early 60's, and so did Bottlehead. Their early SEX amp was the vertical section of a TV set using a 6DN7 I believe.
Yes pleased that you do not say that tube amps are sentient🤔… unlike some recent comments about AI… how could they possibly say that with all the terrible ‘Art’ being synthed now by anyone with a decent NVIDIA GPU… I digress
Anything useful that can be done with a less regular source?
Great story, I’m constantly bewildered by how much I don’t know there is to know about electronics and how we got to where we are today… but I feel I’m on the edge of learning more about early 1950s tech than I know about anything after the 80s electronics and that’s not a whole lot
Whatever source you use will be amplified with some distortion and sent to your "load." If the load can eat a somewhat distorted line voltage it will work fine. I used an old vacuum tube audio generator because I had it. Anything that can produce a waveform that your load can handle will work.
It's pretty easy today to load a WAV file onto an SD card and play it with a Raspberry Pi, a Teensy or other Arduino compatible, or even an old smartphone. Feed this into your amp. The amp will produce a certain voltage at maximum undistorted volume. If this voltage is not enough for your load a suitable transformer will be needed to step up the voltage. Since HiFi is not really needed here, anything that has the proper turns ratio and can handle the power needed by the load will probably work, but only testing will tell for sure. Note, Do NOT feed the output of a mid power audio amp into an automotive ignition coil if you are not prepared to channel up some Tesla! Nikola, not the car.
This is one of those "experiments that could end badly" so don't use an amp or transformer that is valuable to you and DO make sure that things are properly insulated and kept away from any user if you are attempting to power something that needs line voltage levels (120, 230 or 240 volts). Just because this is the output of your amp doesn't mean it can't fry you!
The output voltage may, and probably will, change as the frequency is varied. Depending on the amp and transformer, it may vary a little, or a lot. Have a meter on the output of this setup at all times and remember that most cheap DVM's can read AC voltage wrong if the frequency is not 50 to 60 Hz.