I had never seen or touched this sort of tube tester before. But upon a request of my good friend I tried to place
a bid for the auction of this US Military Hickok TV-3B/U, which needs total repair and calibration.
Yes, sir, I managed to win this auction at Ebay, and got the tube tester for a relatively low price. And the tube tester arrived in good shape, and I checked up its function, and it turned out that it was a totally broken tube tester.
The totally broken tube tester: what it was like.
At first, when I checked it, it only worked when I measured the DC volts in its circuit tester mode. However,
the meter indication was not correct at all. So I doubted the electrolytic capacitor. And later when I got the meter checked by my friend, it was found out to be all right. But this guy found that there were some circuits non-existent.
As I had no schematic diagram, I downloaded from an American website, Instruction Manual and Schematic at the same time.
O-Adjust circuit was non-existent:
It took over ten days but I found O-Adjust circuit non-existent, also no serenium rectifier, and no R-105 resistor between the push-on switch and the secondary terminal of 117V. So by trial and error, I managed to produce 0-Adjust circuit, with silicon diode rectifiers(200V, 2A Hitachi diodes) and R-105 was specified as 142K ohm in the schematic, but by experimental connections, I found out that that value is not suitable for this tube tester, and I found 4k ohm resistor is just it.
After that I was able to zero-adjust the tube tester, but still it did not work as a working tube tester at all, there
was no signal at all when pushed P 3 Mutual Conductance button, so I had to check everything, and it took many
many hours.
No Signal Voltage/ Total Voltage Check-up:
Anyhow, I tried to see the voltages of every portion:
Plate voltage 203VDC, Screen Voltage 160VDC, Bias Voltage 140VDC. These are all wrong,
something is strange somewhere. I doubted the wire-wound resistor 9.5K ohm, so I replaced it by the one my friend brought me. But still it did not improve the tube tester's condition, and then my friend suggested that it has a bad variable resistor for bias control, and surely it was defective. It was open in its center, and there was no continuity between the terminals, And this VR is very hard to obtain, so I had to take out a variable resistor from my TV-7 for parts that I had bought at the auction site. 3K ohm VR for bias control.
Voltages Have become Normal, but Still Abnormal:
By placing this resistor as Bias Control resistor, plate voltage has become 150V, Screen 140V, and Bias voltage, 40VDC, so every voltage has become normal. And then I switched on the tube tester, and again tried to check it up through and through, but when I tried to check mutual conductance, still the meter deflected over full-scale, so I doubted the shunt resistors, and checked every shunt resistor, and one resistor was over 140K ohm and somewhat too strange, and I used my decade resistor and tried to rectify the value. and I gave some resistor in parallel connection with that 140K ohm resistor, 820 ohm in value.
Meter Deflects Over Full-scale:
After all these jobs, I tried to turn on the switch, and I still found the deflection of the meter is not stable,
and indication was not normal. I doubted the shunt resistors would not be correct, and checked them by my digital multimeter, and checked all the wire-wound resistors related; R-112, R-114, R-116, R-119/ R-115, R-123,
R-121 and R-122. In my experience, these shunt resistors are not always the same as in the schemantic, and only when some resistor is extra-ordinarily high or low, it should be replaced, and/or if the meter readings are all right, it is all right. With this tube tester, the resistor named R-114 indicated it was 104 K ohm instead of its original value 41ohm, So I connected my decade resistor, and connected 800 ohm resistor in parallel, to prevent the meter needle go beyond full-scale every time I push on P3 mutual conductance SW, and after I connected 800 ohm resistor. I tried to check the tester, but this time it stopped working properly. It puzzled me a lot.
I had first doubted the capacitor connected in parallel with the meter, 100uF 16WV, elecrolytic, I disconnected this capacitor and replaced by another one, relatively new but used one I had at my hand, and after that
everything has become perfect! So after eighty hours or so struggle, I have succeeded in repairing this
tube tester, very beautiful but did not work at all at first, but now working all right.
I succeeded in repairing and restoring this tube tester.
Thank God!! It works all right now, it has come back to life!!
