Choose the Best Tube for Metal
Customer’s Choice: the Best Rated Tubes for Metal
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Best Tubes for Metal – Buyer’s Guide
Tube amplifiers are offered in the form of preamplifiers, power amplifiers, and integrated amplifiers. Hybrid designs of tube and transistor also occur. There are many types of tubes: Mostly pentodes and triodes are used, for example, the EL34 or the 300B – two absolute classics. To emphasize the classic look, some models have VU meter displays. On the rear, there are mainly analog connections such as RCA or XLR, speaker screw terminals, and, more rarely, headphone outputs. Increasingly often, digital gimmicks such as USB or Bluetooth are integrated. If you are the record player’s owner, you should definitely make sure that a phono input is also offered before buying. This saves a separate phono preamplifier.
A tube pentode consists of a cathode, an anode, a control grid, a screen grid, and a brake grid. The flow direction of the electrons in the pentode is from the cathode to the anode.
The cathode consists of a wire and the anode of a collecting plate for the electrons. The control grid is located between the anode and the cathode and is often represented by a wire mesh. This whole construction is enclosed in an airless glass bulb.
If the wire at the cathode is now heated, electrons are released. Since electrons are negatively charged, they are subsequently attracted to the positively charged collecting plate at the anode.
This current flow can only be generated in one direction in the pentode since the collecting sheet is not heated, and therefore no electrons are released at this point.
With the control grid’s help, it is now possible to control how strong the current flow is within the tube.
Since the control grid is located between the anode and the cathode, it can prevent electrons from flowing through. The control grid is also negatively charged when a voltage is applied. The stronger this voltage is, the more electrons are prevented from flowing through. Since the electrons are negatively charged, and the control grid’s wire mesh is also negatively charged, the electrons are repelled.
Small changes in the voltage across the control grid have correspondingly large effects on the current flow within the tube. The current flow within the tube represents the amplified signal. Because of this property, this design is suitable as an amplifier and is therefore still very often used in hi-fi applications.
The screen grid is also located between the anode and cathode. It serves to shield the control grid from the anode’s electric field, and it provides a constant voltage with respect to the cathode. This results in a uniform acceleration of the electrons. This prevents disturbances caused by unwanted changes in the electron flow.
The brake grid also lies between the anode and the cathode and helps to direct the slower secondary electrons back to the anode. These electrons would otherwise break away from the anode and flow back to the screen grid at low voltage. This would result in unwanted distortion.
Tubes wear out quickly. Doesn’t this mean that I have high follow-up costs?
The lifetime of flawless new tubes should not be underestimated. Preamp tubes like ECC81, ECC82 or ECC83 (12AT7, 12AU7, 12AX7) last for 10.000 hours.
Even power amplifier tubes, which are exposed to greater thermal stress, usually achieve a service life of well over 2,000 hours.
I would like to try out whether my tube amplifier changes in sound by other tube equipment. What do I have to pay attention to?
Make sure that you only use tubes of the same type. For some circuits, there are several permissible types (e.g., there are amplifiers that allow the use of EL34, 6550, KT77, or 6L6). In case of doubt, always ask your dealer or the manufacturer!
If the amplifier provides a manual quiescent current setting, this must, of course, be carried out after each tube change.
For many tube types, there are still old stocks of formerly very renowned manufacturers. Is it worthwhile to replace the modern Chinese or Russian standard stock with the old classics?
Yes and No. If you want to use so-called NOS goods (New Old Stock = old unused stock), e.g., from Telefunken, Valvo, Mullard, Siemens, RCA, etc., we advise buying from a reputable dealer. Many windy offers have nothing to do with “NOS” (they are mostly just O – old).
Depending on the tube type, the individual brands and types enjoy a legendary reputation. However, it remains essentially probably a matter of taste.
Aren’t tubes, particularly sensitive components?
Tubes are actually particularly UNsensitive electronic components. There are tube radios, which still do their service after 60 years with the first tube assembly. Or think of Russian military jets, which even today are deliberately equipped with tubes instead of semiconductor components.
You also don’t need to handle tubes with gloves. They are not halogen lamps that would be damaged by the hand sweat that burns in.
What are the so-called “matched” tubes?
Even of the same type and from the same manufacturer, Tubes vary relatively widely in their technical data. After measuring important characteristics, tubes with very similar characteristics are combined into “matched” pairs, quartets, etc. (and – due to the relatively high effort – offered at higher prices).
Please check with your dealer or the manufacturer of your amplifier if matched tube sets are needed.
I suspect that my tubes are “receivers” for interference. What can I do about it?
Sometimes, there are tubes of certain makes that can be somewhat susceptible to interference and microphonics, depending on their intended use.
Remedies are the use of low-microphony types (good dealers have such special types on offer) and/or, e.g., the use of metallic shielding cups around the tubes’ glass bulb.
Do tubes require special care?
No, not really.
Sometimes, especially after a tube change, the contact between tubes and amplifier is not very good (which might be noticeable by one or the other “crackle”). In such a case, it helps to clean the contact pins of the tubes with some sandpaper or a glass fiber pin.
Which speakers are best suited?
There is no patent remedy, which speakers reproduce the optimal tube sound. However, they should not be too power-hungry because the wattage values of many tube amplifiers turn out rather low. Again, the speaker’s impedance should not fall below 4 ohms, while the amplifier impedance should be below the speaker impedance. How well the amplifier harmonizes with the loudspeaker can only be seen by a listening test. Here it is definitely worth taking a look at the trade journals: The experts regularly test suitable combinations of tube amplifiers and loudspeakers.