Reliability on Tubes Amplifiers and Prevention

In hand wired amps (which do indeed last longer, especially in tropical environments) the wiring is not soldered to the tubes. Just thought I ought to clear that up.

In a hand wired amp, the tube socket pins can move more freely, allowing the tube to adjust to dimensional changes due to heat. PCB sockets do not allow this. Hand-wiring also allows one to control inter-wiring capacitances, often resulting in greater bandwidth, plus the quality of the wiring can be controlled.

Heat is the enemy of tubes, wiring and components. If a circuit board is properly laid out though, heat should not be an issue.

It is simply a cheap way of doing things.

Hello Mr. Paulo Ramirez,

Just my opinions to your good questions.

Vacuum tube electronic circuit reliability should be the same whether a PCB (printed circuit board) or point to point wiring technique is used provided both are connected to quality tube sockets and the circuit board is of proper thickness and mounted properly. Yes, to much heat on a circuit board can be a bad thing but they are pretty tough.

The heat generated by vacuum tubes is intentional as tubes requires high internal temperature to operate. A fan used to cool down the heat in a chassis so the other electronic elements do not overheat is a good idea but isn't always necessary. In many cases, tubes are mounted on the top of a chassis and open to air flow so no fan is required. There is some good discussion elsewhere about how adjusting/reducing the voltage to the tube heaters (filaments) can have some advantages but there must be enough heat to make them operate - another whole story for another time.

One thing that can prolong tube life is to have a slow warm up on the filaments. You may have noticed that household incandescent light bulbs usually burn out when you first turn on a light and rarely when they are already on. That is because the initial "shock" from going from 0 volts to 120 volts cause a sudden change on the tungsten filaments from room temperature to high temperature which causes them to break. The same can happen with tube filaments.

Installing inrush current limiters (a passive electronic component) of the proper value in the proper place (either on the filaments themselves or on the main power transformer - or both) can help reduce the initial high startup current. Inrush current limiters are beneficial for both tube and solid state designs if done properly. They are basically resistors that start with a higher resistance when cold and lower resistance (some near 0 ohms) after they heat up due to current flow passing through them. Other slow start up solutions are available but can become more costly or complex.

If tube equipment is designed properly, many vacuum tubes can and do last for decades. If the tube filament doesn't burn out and the tube is used well below it's maximum output ability, it can last for a very long time. I have some that are over 40 years old and still working - much like me - LOL.. :)

There is a lot more to your questions that we could discuss but that could get quite involved and I'm no expert but I'll be glad to discuss this further if you want to e-mail me at glassaudio@comcast.net

Brad

If direct wiring the tubes is better, why doen`t Audio Rearch, Conrad Johnson, VTL, Manley & almost all other hi end tube mfgs. direct wire the tube pins. The only way to eliminate excessive heat is to eliminate the pwr. tubes. If these cos. don`t buy into your line of reasoning or the very few cos. that direct wire, why should I? I prefer the solid engineering approach of the cos. I cited. Maybe someone will agree w/ you. Good luck & good listening.

Well for my understanding tubes on PC boards can easily transfer the heat to the PC board affecting the board itself and components close to them. However when they are wired it's harder to the tubes affect the rest of the components close to them because it is no PS board to share the heat.
If I'm wrong please explain your point of view.
Thank you
Paulo

Who claims tubes wired directly to the pins are more reliable than tube sockets on PC boards? A fan is always a good idea w/ tubes. As far as potential problems tubes are more apt to pass DC, more susceptible to RFI & noisier.