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Mod to Microwave Transformer HV
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DVMs - Top measures Filament #2 ACV, Bottom Beasures both Filament #1 DCV and Bias |
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Powerstat controls Filament #2 ACV, 0 to 16 Volts |
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Plate voltage no load
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HV on, 47.1 VDC cutoff Bias
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60 mA Ip, 29.7 VDC Bias
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240 mA Ip, 14.1 VDC Bias
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Rear View
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Bottom view. Socket top, Fil Xfmr #2 Center (Ebay item), Fil Supply #1 Right, Step start bottom |
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This is a bottom view of the socket with finger stock I made special for this project. Bias board is upper left |
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This is my bias board with slight mods for this application. It uses the common circuit built around the TL431A. |
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Output of wall warts goes to zeners and filter caps to power DVMs at 5V each.
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Ip and Ig meter calibration ten turn trim pots.
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Cutoff bias resistor and shunts for Ip and Ig. Also underside of Banana Jacks for Fil #2 and ground. |
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Back panel switching
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Fil #1 12.6V switching supply from hamfest.
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Fil and HV power switching
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Two wall warts to power the DVMs and below that is the step start circuit
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Power input and fusing |
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Rear panel AC input and primary fuses
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Rear view showing the blower. This one is too noisy for an amp but great for this project.
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Back of digital meters. These came from Marlin P Jones. |
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I built this special socket. Unlike the socket I sell which firmly clamps the grid to the plate, this socket uses finger stock so I can plug a tube in. |
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Glitch resistor and filter caps. The mount for the capacitors was changed in the following pictures.
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Microwave transformer. The voltage sags under load but it is much lighter than anything else. Magnetic shunts are removed. |
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Top view showing the socket, the banana jacks for extending filament and ground connections to different tube adapters, meters and high voltage supply. |
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The capacitors and diode bank are fastened to the chassis with a new Polycarbonate plate that I cut and milled slots in to allow for zip ties to wrap around it. |
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Closeup of the milled slot. |
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A small drop of silicone sealant is put under the end of each capacitor to keep them from sliding around.
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Ties are arranged so the large end doesn't protrude below the mounting plate. |
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Another view of the mount. |
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Test adapter for the YC-156, YC-179 and 3CPX5000A7. |
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Test adapter on the tube tester with the chimney removed. The chimney was made from a plumbing drain and turned on the lathe.
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Closeup of the adapter showing sub chassis where the tube grid ring is fastened. |
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Another view of the adapter. |
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Test adapter for the GI-7B.
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Test adapter for the GI-7B shown in place on the tester. You can see part of a Teflon chimney in the lower right corner..
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