Galaxy Vintage Collectibles

USING VINTAGE ITEMS TO MAKE A DIFFERENCE

All of my earnings from this site support me in my work with many poor and unfortunate people in India, Rwanda, Kenya, Uganda and Mozambique. I work with Open Arms International in operating medical clinics and educational outreach to those who have been victimized by Malaria, Typhoid, Leprosy, AIDS/HIV and other devastating diseases.

Please visit our site: www.openarmsinternational.com for complete information. I am also a seasoned and experienced pastor (40 years) and support and reach out to local pastors in those countries.

My two specialities are 1.) repairing and reselling vintage musical instruments and, 2.) selling vintage electronic instruments and vacuum tubes. I currently have an inventory of 10's of thousands of vacuum tubes in stock and have sold to satisfied customers all over the world from Australia to Greece, Taiwan to Brazil, etc.

HOW WE TEST TUBES Or Why does that expensive matched set I bought sound so wrong??? Most of the Tube Testers in circulation today were made for the mobile TV repair man. The good ones, like Hickok, did an excellent job of detecting bad tubes. But detecting a bad tube is not the same qualifying a good audio tube, and that is what you must know before you buy.

The best way to test is to listen with the tube in the actual amplifier for an extended time. Unfortunately this is a very expensive and time consuming process. A close second is to examine the tube dynamic traces. Running a very, very distant third, fourth, and fifth is using a tube tester. If you are replacing a TV tube—trust the Hickok. If you are buying audio or guitar tubes, you need better tests.

To understand why, look at the (above) tube trace of a vintage 6SN7 that sold for a high price as "perfectly matched" between sections. In reality this tube is at the end of life and in terrible shape. (Note: many of the new tubes from China look like this or worse out of the box, but for the vintage tubes of American and Euro design—this is a bad tube.) The pairs of lines represent the response of this tube to a signal such as would come from a CD player. The red circle marks where a typical tube tester would test a single point. In that area this tube looks prefect, but the overall picture is much, much different. The lines should be parallel and equidistant. Parallel means similar performance, whether new or used. Equidistant means that the response will be linear and correct for any amplifier.

Here is a second example (above) of a tube, which according common wisdom, does not match. This tube (GE 5751 from 1966) has beautiful and even sound. Why is that? The red line indicates the region where this tube will operate. Even though the pairs of lines are not identical, they are parallel and equidistant where it matters.

But what about the fact that the amplification is different between the sections you may ask? In point of fact this tube measures with a Gm of 1880 in one section versus 1780 in the other section. Let’s continue by asking:

WHAT IS MATCHING? T

Tube matching is poorly understood and misrepresented most of the time. Let’s state what matching really is in the audio world: Matching is simply two tubes or sections that produce nearly the same response to the same stimulus as perceived by the listener. Just like the tube in the second example above. From the audio perspective the difference in the gain of the GE tube above results in volume difference of about ½ db. This is completely inaudible to the human ear—1 db is defined as the minimum difference that can be detected. That is why the good sellers specify 5% tolerance as “closely matched”.

Matching is not:

2 boxes identical boxes

2 identical date codes

The same manufacturer

The same value on a tube tester

WHEN IS PERFECT MATCHING IMPORTANT?

The right answer is seldom. Some very high end tube designers used to specify mismatched tubes for their designs. Other inventors expected tubes not to match and designed appropriately. There is, however, one place where matched sections or tubes are important. This is wherever a two amplifiers work together to produce a complementary parts of a signal. Differential amplifiers are the main example for preamps. If you have a preamp that produces balanced outputs, differential design is most likely used. If unsure, contact your manufacturer.

All of our best audio tubes are put on the tube tracer and the results are supplied so that you can see exactly what you are buying (see our satisfaction guarantee.)

The second place where matching is desirable is for power tubes in push-pull amplifiers. It is good idea to match the current draw in guitar and audio amps with tube pairs or quads. The amp will be balanced if the current draw is matched. I would much prefer to use a used matched pair of power tubes in a push-pull amp than a mismatched set of NOS tubes. Power tubes all wear out over time, and a used set of matched power tubes has really good value. These tubes are broken in and can be expected to perform in the matched manner for some time. This brings us to the last point of this tutorial.

HOW SHOULD POWER TUBES BE MATCHED?

There is only one right answer. They should be matched in the method they are used. That means high current draw—which you cannot get from almost all tube testers. All of our power tubes are measured with current draws that simulate class A performance, after a minimum of a 15 minute warm up. We use either a tube tracer or a custom modified OTTO Power Tube Matcher from Sovtek to do the testing.