Calibrating Hickoks

"Don't forget to allow some Kentucky windage..."

Most Hickoks, from the 533 to the 799 calibrate in the same way, apply a "standard tube" and adjust. In most cases that standard tube is a 6L6 - Hickok even sold a simulator as well as the real thing.

However for the modern hobbyist, it is easier to just construct a fixed current source since that is really what is being measured. Materials are not too hard to come by: a 10K resistor of at least 4 watts, an isolated AC source, a variac, and a means to measure current. NOTE: the isolated a/c source is very important for any shop as many chassis and circuits used a reversible plug and a hot chassis. Connect a grounded instrument to the circuit and something is going to fail. Store-bought is best of at least 150 ma (again, more is better). Hooking two 120v-12v transformers back to back will do the same thing if that is what you have.

In the best of all worlds, plug a variac into an isolation transformer and put the 10K resistor and a fused ma meter in series with the output. Set the Tester up as if for a 6L6 after allowing warm-up and setting the line voltage. Plug into pins 3 and 8 (6L6 cathode and plate) of the octal socket. Adjust to 5 ma. Divide 5 ma by the grid signal in volts and you get millimhos. Multiply by 1000 to get micromhos.

For example, with a grid signal of 2.5vac (typical of the 600 series and many other Hickoks in the 6L6 configuration), this would be the equivalent of 2,000 micromhos and should be set on the 3,000 scale.

If the unit does not read in micromhos (TV-2, TV-7, 799) there is a problem however fortunately most Hickoks do have a micromho scale though it may not be obvious (on the 600 series micromho calibration is by setting to a small dot on the SHUNT dial).

NOTE: What is listed on this page is a means to verify calibration. Adjustment varies by model and in some cases requires replacing resistors. Nothing on this page requires removing the chassis from the case.

Daniel Schoo prepared detailed calibration procedures for the Model 539 and the Model 600

TV-2

TV-2s read in "percent quality" fortunately this is translatable as follows (thanks to Alan Douglas):

range	grid	shunt	full scale Gm
	vac		setting
A	 .25	55	30,000 
B	 .25	37.5	15,000
C	 .25	37	 7,500
C	 .25	86	 3,000
D	 .5	86	 1,500
E	2.5	86	   300

Simple check would be to set up as for a 6L6 with the 5 ma simulation circuit above on range C with shunt set to 86 and verify 2/3 scale reading when the mutual conductance lever is pressed.

TV-7

For the TV-7, the setting is HS-53460 function B shunt 0. Connect 5 ma AC (50 vac with 10k series resistor as above) source to Octal socket pins 3 and 6. (only Hickok to use pin 6 instead of 8 for this, possibly avoids an internal interconnect). Note: filament setting is irrelevant since not a real tube.

1) Depress MUT COND button 3. Meter should read 40 +/- 1/2 div. (if meter deflects negative, reverse power plug).

2) Set function sw to C. Depress button 3. Meter should read 20 +/- 1/2 div.

3) Set fn sw to D, depress button 3. Meter should read 40 +/- 1/2 div

4) Set fn sw to E, depress button 3. Meter should read 40 +/- 1/2 div

5) (TV-7D only) set fn sw to F, depress button 3. Meter should read 40 +/- 1/2 div.

Cardomatics require special test cards. This can be simulated as above for 6L6 using pins 3 and 8