Hickok 538A Mutual Conductance Tube Tester and Analyzer

One of the rarer Hickok models, I purchased this unit, manufactured in 1951, (our demo unit) in May 2006 and use it daily in my shop. It was due for calibration in '07 but still performs in the parameters as it did when I purchased it. Roger Kennedy calibrated for the gentleman I purchased it from just prior to that time. I own two other 538A models. One was manufactured just after WWII and looks as though it came through a "war zone". It nonetheless is a working tester and is an excellent back-up to the other two. The other 538A was used on the testing line at Western Union Telegraph Corporation and actually shows very little service. The unit and case are in exceptional condition. This tester was manufactured in 1948. The individual I purchased it from received it from his dad, a Western Union employee, when Western Union was divesting itself of out-dated and surplus equipment. He purchased it for around $30. I was fortunate to receive with it the original Hickok 538A manual as well as the manual for the tester written by the Engineering Department of Western Union. Both manuals are similar with Western Union adding a few of its operating notes regarding the 538A as well. The 538A manual is not available on line as an original, a reprint or as a download. Prior to a couple of years ago, I daily surfed Ebay pages; and I always checked the Hickok offerings. I had perhaps seen 6 538A's in as many years as I surfed, and I purchased three of them. Never in that time was a separate manual for this tester offered. Hickok equipment is rugged, well-engineered and highly sought by restorers of vintage electronics as well as those of us who enjoy paying the bills restoring vintage equipment. The "Western Union" 538A required only one capacitor which I installed as an "update"; and the other used as the demo has required no maintenance since I have owned it.

The 538A utilizes two transformers whereas lower-priced models use only one. The 538A uses one transformer for filament voltages and the other for testing mutual conductance. The other models used one transformer with two separate windings.

Beginning in 1951, Hickok installed a no. 49 bias fuse on the tester deck just below the Bias pot to protect the Bias potentiometer from burn-out. Failing to check a tube for a short or setting up the controls incorrectly will usually pop the fuse. This little add-on has saved my butt on several occasions. I have installed a bias fuse on every Hickok I own. The no. 49 bulb must be replaced with an identical replacement.