Download HICKOK B TRANSCONDUCTANCE TUBE TESTER service manual & repair info for electronics experts. Daniel Schoo produced a classic document on calibrating a Hickok B/C tube tester which was published in on AudioXpress. Hickok B/C Mutual Conductance Tube Tester – Checkout and Calibration. Version Use this procedure to test and calibrate the Hickok Model C mutual .
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Make one range better and you make other ranges worse. Constant Current Calibration Sources.
Accurate Calibration Of The Hickok 539B And Hickok 539C Tube Tester
The usual definition of transconductance is as the ratio of the change in plate current divided by the change in grid-to-cathode voltage that causes it, all other voltages on the tube being held constant. Douglas on the Antique Radio Forums site and he acknowledged that that statement was an error in his hickokk. Okay, I made that last part up, but you get the idea, I hope.
The following data is based on computer simulations of the transconductance measuring circuits except for the actual calibration results of my set and assume the following:. If you are only interested in checking the calibration, this section can be omitted.
Accurate Calibration Of The Hickok B And Hickok C Tube Tester
Consider the graph of Figure 16 Calibration Tube Plot which illustrates this. Skip to main content. If there are any failures here, you probably have a poor contact in the 539g switch somewhere. The circuit is such and the values are such that the junction of R19 and R17 is at approx. You could also change R7 1. However after extensive work with the simulations, I did eventually find a set of resistor values as given above, that significantly theoretically improve the accuracy in the transconductance sensing circuitry without requiring excessive changes.
You simply adjust the value of the op amp feedback resistor to suit your particular meter movement. Even for regular power diodes, the applied voltage is fairly small 35 VAC max.
If the leakage is greater than that corresponding to a Kohm resistor, it will light the neon bulb on the 1 to 4 SHORTS switch settings anyway and the tube would be discarded, so accuracy around 0 ohms is unimportant. This assumes that each channel of the amplifier in question has only one bias adjustment that simultaneously affects both push-pull output tubes of that channel.
Remember, one point value and one slope value is all it takes mathematically to uniquely determine a line. If C3 were not used, the physical inertia of the meter movement would perform the same function.
Hickok B Tube Tester Instruction Manual & Tube Data | eBay
If not correct, adjust R18 8. First, a little theory: The engineers who design tube equipment are well aware of these considerations and usually design their equipment to be able to tolerate this variability, at least up to a point.
Slightly different test conditions would be expected to give slightly different transconductance values. Note that these 83 and 5Y3 SS replacements are specifically tailored to this set and should not necessarily be considered general replacements, although a 5Y3 SS replacement with to ohm resistors and 83 replacement with or without the manuxl volt zener diodes will, in most cases, work about as well as if not better than anything you can purchase on the net or elsewhere.
Schoo method actually compromises the over-all accuracy.
Read on to see why I say that! There are 6 transconductance ranges and to accurately calibrate all 6, it would require 6 separate non-interacting zero adjustments and 6 non-interacting gain adjustments.
If you substitute a 6. The miniature and sub-miniature tubes use very close spacing between the tube elements. Engineering design is always a set of trade-offs, and at the time, this would have been considered good engineering practice.
It is also very important that the meter used for the actual calibration be able to accurately measure the relatively small AC voltage 5. Thus the effective resistance of the tube varies not only from tube to tube and as the tube ages, but even in the same tube depending on the total plate current.
As for microphonics, as far as I know, no conventional tube tester actually tests for this. Actually, it does more than this, it also puts a K resistor R36 in series with the neon bulb and puts a K resistor R35 across the combination. Second, the grid bias voltage is actually a series of half waves of a 60 cycle sine wave which means it goes from 0 V to As a concrete example, consider an experiment measuring the transconductance of a 6L6GB tube as measured on a Hickok B mine, actually, but long before the modifications and before even very accurate calibrationwhere the transconductance measured about Micromho in the C range and Micromho on the D range, a difference of about 5.