Tubes in Parallel (Part 2)

Pictured is a schematic of a Freed-Eisemann NR-7 radio receiver from the 1920s. Besides being an interesting example of the primitive circuitry in use throughout the ‘20s, this receiver also illustrates using output tubes in parallel — without any kind of balancing circuitry! All of the leads are tied straight together, which would cause some … More Tubes in Parallel (Part 2)

Tubes in Parallel

In hi-fi tube amplifier building, a frequent temptation is to use two power tubes in parallel. After all, it is a simple way to double the output power – provided, of course, that you change the audio transformer’s impedance to one half of the value you would use for one power tube. However, in practice, … More Tubes in Parallel

Output Transformers

The output transformer is arguably one of the weakest links in a vacuum tube amplifier, hence the rise of output transformerless (OTL) vacuum tube amplifiers. There is a problem with this arrangement, however. Driving a speaker directly with a tube results in a terrible damping factor and very high distortion levels. This is why OTLs … More Output Transformers

Tube Rolling for Sound: JJ KT88, Genalex KT88, EH KT90, Tung-Sol KT120

  I must admit that in my previous article on tube rolling, I didn’t go too much into the actual sounds of the tubes used. I long delayed in adding that detail. However, it was all for the best — for I’ve added the JJ KT88 to the list of tubes in this comparison. If … More Tube Rolling for Sound: JJ KT88, Genalex KT88, EH KT90, Tung-Sol KT120

A Simple, 5W, 4-Tube Hi-fi Single-Ended Triode Amplifier

Sounds cool, doesn’t it? Here’s a chance to build your own amplifier – a simple design with outstanding sound quality. We are offering the schematic absolutely free, and we think you will be surprised at just how good the sound quality of this amp is.   Let’s Go Inside There are four tubes, two per … More A Simple, 5W, 4-Tube Hi-fi Single-Ended Triode Amplifier

The JJ ECC99 Tube

Now here’s a current-make tube well worth becoming acquainted with! While I have heard the excellent sound of the Sovtek and the Electro-Harmonix 6H30PI “super-tube,” I must confess that, while as excellent as they are, they paled in comparison to the JJ Electronics ECC99. And no, we are not affiliated with JJ Electronics in any … More The JJ ECC99 Tube