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To answer my own question, the data sheet for the EA53 shows it to have an indirectly heated cathode. In general, tubes with indirectly heated cathodes want to be operated at very close to the specified voltage. In this case 6.3 Volts, as indicated in the later instruction book and update. The Eimac tube runs at 5 Volts, so I suspect whoever set the voltage previously did not see the change. The modification is noted on a sticker inside the back cover from a Hewlett-Packard service center. The tube actually in the probe is the Amperex tube. I doubt -hp- would have mis-set the voltage but that was a long time ago and I expect the unit will have been calibrated many times since then.
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Someone may have thought the lower voltage would extend the tube life but that is not recommended for indirectly heated tubes (most receiving tubes) and it would undoubtedly affect the tube characteristics and calibration. I still want to know about other's experiences. On 6/15/2024 4:55 PM, Richard Knoppow wrote:
??? I posted recently about my ancient 410B, which I finally repaired. I have a question: My meter was modified for the Amperex EA53 RF rectifier. In the handbook it states that the filament voltage for this tube should be set to 6.3 volts. I checked mine and found it was set to slightly more than 5 volts. That would have been correct for the Eimac rectifier. My question is was there some note somewhere about setting the voltage for the EA53 lower? In any case I set it for 6.3 volts, with the line set to 115V on a Variac. I checked the calibration and found it had not changed significantly. I had set it before with the lower filament voltage. --
Richard Knoppow Los Angeles WB6KBL SKCC 19998 |
