Sencore tc 28 manual

The test places approx 34 VAC between this one selected element and all other elements. As your rotate the Selector switch from 1 to 12, all tube elements are compared to each other. If the selected element has a short to any of the other elements, the Neon lamp models TC and TC will light. The Neon lamp will just barely glow at K, and will glow brighter as the condition approaches solid-short. This method has less accurate shorts detection, though.

Using the 6KG6 example, a real short between the screen and suppressor would not be properly detected because those two pins would normally show short anyway — and the tube chart would tell you that is correct behavior. In reality, this limitation in the TC affects only a relatively small number of tubes tubes that have multiple elements that each have multiple pin connections.

If you find a beautiful TC, I would not hesitate to buy it, as this limitation is rather minor. These shorts would not be detected on any tester without lockout switches, regardless of tester brand. The K detection will be close is the circuit is working correctly. Model TC28 does have a procedure explained below to calibrate the Shorts Test to factory specs. The circuit engaged on the front panel by a thumb slide switch switches a small resistance 1-ohm in series with the filament voltage, which drops the filament voltage to the tube under test.

The result is a true life test that only drops the filament voltage, while leaving the cathode emission load voltage unchanged. It works very well. The effect is significant when testing rectifier tubes and power output tubes.

For example, while testing a new 5U4GB and engaging the life test, the emission reading is largely unchanged. When testing a used 5U4GB and engaging the life test, the emission reading will drop.

While there is no fixed rule as to how much drop is acceptable, the less the drop, the better. A good rule of thumb is that if the emission drops into the red area, the tube is suspect. If the emission drops into the questionable area, the tube probably has useful life left. If the emission remains in the green, the tube should have comparable lifespan as a new tube. Make sure that you have a service manual.

It contains circuit description, schematic, voltages, parts lists, troubleshooting chart, and calibration procedure. After years you should expect that components fail — carbon resistors change value, wires break off under the testing sockets, contacts and switches are dirty and corroded, etc.

Therefore, these things must be thoroughly checked before anything else is done. Check and replace all non-spec resistors, paying close attention to the load resistors. Check or replace all capacitors. Treat all sockets and switches with Deoxit. Look carefully for wires that have broken off from the sockets or worn insulation causing shorts to the chassis or adjacent wiring.

Check continuity between all socket pins and proper continuity of Lockout switches models TC and TC Check secondary transformer voltages filament voltages and Load voltages. Check circuit board voltages as marked on the schematic.

Voltages are taken in reference to the - side of electrolytic capacitor. Some models have an undocumented AC line resistor in series with the transformer primary.

Approx ohms resistance, high wattage, and may be two 50 ohm resistors in series. The purpose is to drop the AC voltage down to V, which corresponds to the schematic documenting the primary as V. This modification is not present on all models even in the same model number. It may have been due to a different transformer supplier, the reason is unknown. The TC shipped with a ground line cord. The later revisions have a 1.

This modification is not present on the TC schematic but can be easily added to a tester missing it. This mod is present on TC28, as shown in the schematic excerpt to the left. If adding a grounded line cord to any earlier Mighty Mites, such as TC, this is a useful modification.

The tester has three parts to its circuit: Emission, Shorts, and Grid Leakage. Common problems: No panel meter reading — check for bad 2N transistor, bad zener diodes, or open panel meter. Emission problems — check the load resistors for opens. Shorts problem — check for opens in each pin circuit loose wires or shorted wires at the sockets , check for shorts to chassis around the sockets, check the 82K and 8. For grid leakage problems — check the two 15Meg resistors.

Note: The case lid will not close on many Mighty Mites with socket savers installed, especially not when installing the octal socket saver. Buy at your own discretion. Now you are ready to use the Sencore Calibration Module, and follow the instructions in the manual. One version of the TC manual says that you should find shorts on 6 and 7.

This is typo, it should read 5 and 6. Grid Leakage calibration using Sencore Calibration Module. Emission calibration using Sencore Calibration Module. I am frequently asked to explain how to make the Sencore Calibration Module, even though I mentioned above that these instructions are in the full Sencore Service Manual. I am adding the Calibration Module instructions here since it is a popular request, even though this is NOT a substitute to owning the service manual. You really should not expect to properly service and calibration any piece of equipment without a service manual and schematic.

This Sencore calibration module is NOT a magic bullet, and using it without performing the prep work above is quite useless.

ALL of the real work is in the circuit testing and preparation. Using the calibration module is nothing more than the last step of the repair process. That said, here is the Calibration Module information and calibration steps for each model…]. Sencore Calibration Module instructions for TC After calibrating, check a variety of new tubes of known value.

The meter should read in the middle of the Green-Good range. Valve characteristic meter. This new outstanding feature means that no time is wasted waiting for the checker to warm up and stabilize before accurate testing can begin.

The new Mighty Mite is ready as soon as it is turned on. A full load cathode current check, high sensitivity grid leakage check, and the famous Sencore Stethoscopic shorts test make this the ideal checker for service work and the man on the go. Service Manual. Board layout Comments No comments yet. Be the first! Add Comment. Notify me of new comments via email. I have read and agree to the terms and conditions.