• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Few general question for starter?

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tomchaoda

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Joined 2003
#1
After completed my solid-state audio from the design of Nelson Pass, I would like to get my feet wet in the tube amp. To start it up, I would choose 2A3 and hopefully make a 300B by using Audiio Note Kit one design. In doing so, I have these following questions and I hope I can find some answer here:

1. Is there any 2A3 tube review out there? I found two very good links for reviewing all current 300B tubes, but I can not find 2A3's!

2. Can any suggest a good FM tuner to match the tube amp without breaking my pocket (around USD$ 300 as top limit!) I have one Sansui TU-717, which is good, but would like to explore a new one.

Thanks,

Thomas
 
#2
tomchaoda said:
I would like to get my feet wet in the tube amp.
Click to expand...

Very bad idea 😀 High voltages and water just don't go together.

I believe that the Sovtek 2A3 is well regarded. I have tested a couple and they seem to conform to the original 2A3 specification. However, one thing I did discover is that the heater voltage is critical. 10% low voltage at the heater pins is sufficient to cause emission to collapse.
 
#3
Please don't mind my asking this simple question. In solid-state world, I know how to test a mosfet is matching well or not!

Is there a way to test a pair of tube that it is claimed to be a "matched pair" when I got it? (particularly is from ebay)?

Thanks,

Thomas
 
#4
MOSFETs have huge device variation. The key specification for a MOSFET is the voltage required between the gate and the source to turn the device on. If you connect the MOSFET with a protective resistor in the drain to a power supply and monitor the current through it, then you can use a 9V battery followed by a potential divider to turn the device on and measure what voltage was required. Devices with equal turn-on voltages are matched.

You can pretty well assume that any valves you buy are not matched, no matter what the vendor says. What were they matching for? Mutual conductance, or anode current? Under what DC conditions? Did they know what they were doing? Did they have the requisite test gear? The best way of "matching" valves is to put them in the circuit and measure how they perform.
 
#7
Thanks for the good tips!

To make sure, I ordered two good books from Amazon:

1. Valves Amplifers

2. Building Valve Amplifiers

both are by Morgan Jones.

At this moment, tube terms is killing me. I hope I can catch up soon! and hope that tubes isn't breaking my wallet!

Thomas
 
#9
tomchaoda said:
To make sure, I ordered two good books from Amazon:

1. Valves Amplifers

2. Building Valve Amplifiers

both are by Morgan Jones.
Click to expand...


Those are excellent books and explain the concepts quite well. I had "Valve Amplifiers" for a while but had to return it to the library🙁 Also, I'm pretty sure Morgan Jones does frequent this forum....😉

tomchaoda said:
At this moment, tube terms is killing me.
Click to expand...

If you don't understand anything, ask for help. It's better then frying something or getting fried😱 There are plenty of people here willing to help
 
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