Tube amplifiers are a great piece of old-time technology that have managed to stay relevant through the ages. One of the advantages of using them is the fact that you can tweak them to a great degree. For example, you can do tube rolling, which is the practice of individually personalizing each tube in the amp so that it performs to your personal taste.
One of the more interesting tweaks that people can do is to add a tube amplifier choke. “Choke” is the usual term for an inductor used as a filter for a power supply. These are usually iron core filters.
They look like small transformers to the untrained eye, but they just have two leads leaving the housing. Their main job is block AC voltage coming through, while letting DC current to pass.
Why Get a Choke?
One of the primary reasons for a tube amplifier choke is the fact that inductors cannot change currents easily. This makes them ideal as a way to smooth out the voltage of your amp. A series resistor can do the same thing, but people prefer a choke for two reasons.
First, there is less rippling in the AC supply with a choke, which causes less humming in the amp output. This makes it ideal for filtering out the AC from the current.
The other reason is a large resistor will cause a voltage drop. Since the current is what translates the sound in the amp, it will cause a noticeable change in audio performance.
Overall, with a choke in place, your amp will have less background humming and respond better in the long run. Besides that, the transformer will have less stress on it, which improves its operating lifespan. A choke can also potentially have several audio benefits. This includes better frequencies response, reduced harshness, and improved touch sensitiveness.
Most of the time, you don’t even need to add a choke. Most power supply configurations for tube amps have a choke already. However, a choke is not something that manufacturers always add. This is especially if they plan to sell for maximum profit.
If it is not there, then you may want to put it in on your own. This is because you may add some more power filtering to your tube amp and get some of the audio benefits. You may also need to replace your current choke with one that you feel will work better.
What to Look for in a Choke
If you decided to add a choke on your own, there are several factors to consider. Chokes have ratings in max DC current, DC resistance, inductance, and a voltage rating. Knowing the reasons for each will make it easier to decide on which one to buy.
Before everything, you need to know what sort of power supply configuration your amp has.
A capacitor input supply has a filter capacitor after its rectifier. It may or may not have a choke already. This power supply type has higher output voltage.
The other type is a choke input supply. Instead of a filter capacitor, a choke is already in place. The result is better voltage regulation, but lower output.
When you know your amp power supply, it’s time to look at the choke factors. First, there is the DC current. Depending on the power configuration of your amp, there are two different requirements.
A choke input filter depends entirely on a choke as its filtering method. This means it needs to handle the entire current of the entire amp. This includes the output tubes and the preamp tubes. You will need a choke that can handle up to 50 watts for this.
If you are choosing a choke for a capacitor input filter, then you won’t need something that powerful. You won’t need to filter the power tubes, only the preamp tubes and the screens. This is usually in amperes not watts. For a typical 50W amp, you’ll want a choke that can handle up to 60 milliamperes.
The next value to check out is the DC resistance. The same factors apply for this as DC current. Choke input and capacitor input have different requirement.
For the former, you will need a choke with around 100-200 ohms of resistance. A capacitor input will need higher resistance. This is usually at 250 ohms to 1000 ohms.
The next factor to consider is the inductance value. As a good rule-of-thumb, the higher the better. This is because the higher the value, the better the filtering.
Finally, there is the voltage rating. This is the simplest to learn about since the voltage rating must be higher than the supply voltage. If not the wire insulation will break down and result in a short circuit.
Installing a Choke
Once you’ve managed to select the choke that fits your needs, it’s time to install it. Before anything though, you’ll need to know that even if it sounds simple, this is still an electrical process. You may accidentally mess up your amp if you’re not careful.
Be very sure about this before doing it. If you think you’ll mess it up, it’s best to go to an actual technician and have them do it. It’s not worth it to completely mess up your amp.
Okay, first of all, you’ll need to find a prime place for your choke. The best place for it is somewhere between your power transformer and output transformer. However, keep in mind that you’ll need to have space for it. Be flexible in placement. Just make sure it is near your power transformer.
Once you’ve set it in place, you’ll need to attach the leads of the choke.
Depending on the model of the amp, you may need to desolder a resistor and solder in your choke’s leads. Check out your amp model first to see which resistor your choke will replace. No need to worry about polarity when soldering in the leads. When that’s done, your choke should be ready to go.
A Simple Upgrade
A tube amplifier choke is a simple upgrade that can change your amp’s performance a lot. Consider it if you want a simple way to improve your sound in every set.
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