![]() ![]() Get a DVM and measure the voltage at the arm of the signal pot Then forget about the scope things in the manual. Max signal first, you adjust the meter at 100% with 2 trimmers. You need a 1600 ohm resistor to the arm of the signal pot, to the 0.47uf cap of the voltage amplifier (marked CAL in to board), as the user manual's instruction. That calibrates the tube voltage differential for all measurement.Ģ) The GM emission calibration is a 2 step process. Then you insert it and adjust the meter mid range with 1 trimmer. All caps in the board, more trimmer, neon bulb on top, etc.ġ) The static emission needs a plug to be build with 2 resistors and a diode, as per the manual. Only one tube mounted on a plate, shielded. I added a current sensing resistor in the meter path so I could connect a VDM to it.Īfter 2 iterations, one without layout change (V1.0) and all these changes (V1.1), I got a perfectly working solution. Add trimmers were I needed to make the calibration easy. I wanted to shield the 12AU7 and keep it tied to the socket. I wanted to only use 1 tube, and replace the OB2 with a solid state solution. Increase within reason the PS filtration. First I wanted all the caps to be mounted on the board and not externally mounted to the chassis. I liked this tester so I decided to make a new board, and improve a few things. I was happy, but the board was still fragile, and the calibration wasn't easy as some resistor needed adjustment and without a trimmer, it the painful de-soldering/re-soldering process, try, retry. So I first tried to change all components on the board and give it a try. Most of the components on the board were out of specs and had to be changed.īut all the rest was in excellent condition. The calibration is unnecessary complicated. The case is a made of solid metal protecting the tester very well. ![]() It has 2 transformers, one for the heaters and one for the tester itself. It is a very robust and heavy piece of equipment. The voltage reference is also made with a tube too, an OB2 voltage regulator. And does a superb job as trans-conductance test, by generating a 5 Khz signal to the tube and measure it that way. It does the classic tests for static emission, shorts, grid leakage and tube life. The meter could pick up variation that my fluke couldn't. It has a very sensitive as it uses a 12AU7 tube as voltage differential. This tester is one of the last tube tester been produced, therefore is more modern than the classic oldies. ![]() I worked of this tester, a Sencore MU-150, that I found very nice so I am sharing this with you. I am not sure this belongs to the Tube Audio forum but I didn't find a more suitable category. ![]()
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