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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta content="text/html; charset=ISO-8859-1" http-equiv="content-type"> <title>tubetester.html</title> </head> <body> <div style="text-align: center;"> <div style="margin: 0pt 0pt 3px 3px; float: right;"> <script type="text/javascript"><!-- google_ad_client = "pub-2883201771825220"; google_ad_width = 120; google_ad_height = 600; google_ad_format = "120x600_as"; google_ad_type = "text_image"; google_ad_channel = ""; //--> </script> <script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"> </script> </div> <div style="text-align: center;"><big><big><big>My 211 Tube Tester</big></big></big><br> </div> <br> <div style="text-align: left;">I've been building electrical and electronic devices since I was a child. Only recently did I develop an interest for vintage vacuum tubes. One of my friends is an avid audiophile. He brought me over to his house and showed me his $30,000 system: Cary Amplifiers, oversized cables, preamps, designer CD player and monstrous audio speakers. I saw his 211 and 300B tubes glowing in the dimly lit room; their glow pulsating with the clearest audio I have heard in a long time. I was definitely impressed with his stereo audio system. He regretted, though, that he did not know if his tubes were properly matched. You can imagine that if someone spends 30k on their system they probably would like to have the tubes function in an identical manner to within a few percentage points.<br> <br> While we were at work he asked me how hard would it be to design and build a 211 tube tester. He knew his Western Electric 300B tubes were matched because he bought them from the factory as a "factory match". They even came with their own plate-current curves that were generated on a curve tracer. However, General Electric and RCA stopped making 211 tubes long ago and there was no way to test his tubes. I went on the internet and found various vintage tube testers: Hickok, Heathkit, Tripplet and Sencore were a few that I found. Almost none could test the 211; only one had the ability to test current conduction at one grid and plate setting. None of them tested transconductance. This would not work for my friend.<br> <br> I started thinking about how to tackle the problem. I have to admit that initially I was a little lost. Most of my experience was with capacitors, inductors, diodes, transistors and transformers. Who used vacuum tubes anyway? I started re-educating myself on vacuum tube theory and how they worked. The vacuum tube is the predecessor to the transistor; it acts as a valve controlling the amount of current that travels across the plate to the filament. Next, I studied the specifications of the 211 tube. The tube handles a lot of voltage, and when conducting maximum current it can put out 100 - 200 Watts. I wouldn't drive the tube to this extreme as this will shorten its life span.<br> <br> Next, I had to design an electronic unit that would operate the tube within it parameters. Except for the casing, I wanted to use vintage parts. The voltage and current meters had to be vintage analogue devices. The circuit design had to be simple, but effective. I got my solder gun, solder and flux ready. My workbench with all its resistors, capacitors and dials was ready. The problem was that there were no schematics available or any suggestions on any web sites on how to build a circuit board for this application. I finally realized that the key to building the tube tester truly understanding how the vacuum tube works.<br> <br> <img alt="" src="IMG_7728.JPG" style="width: 432px; height: 288px;"><img alt="" src="IMG_7729.JPG" style="width: 432px; height: 288px;"><br> <img alt="" src="IMG_7730.JPG" style="width: 432px; height: 288px;"><img alt="" src="IMG_7731.JPG" style="width: 432px; height: 288px;"><br> <img alt="" src="IMG_7732.JPG" style="width: 432px; height: 288px;"><br> </div> </div> </body> </html>