1. 4HA7 is a dual diode-pentode vacuum tube with a 9-pin Miniature (Collins) base. It was developed for use in television receivers, where the high gain of the pentode section could be used for the RF and IF amplifier sections, with the diode section available for the detector and AGC stages.
2. 4HC7 is a four-diode-pentode vacuum tube with a 9-pin Miniature (Collins) base. It was designed to serve both as a double tuned RF amplifier, as well as a high gain IF amplifier, using the pentode section. The diodes were intended to be used as detectors, AGC, aligning, and video amplifiers.
3. Both the 4HA7 and 4HC7 use a 9-pin miniature base. The 4HA7 is a dual-diode/pentode combination with a 9-pin miniature base, and the 4HC7 is a four-diode-pentode combination with a 9-pin miniature base.
4. 4HA7 and 4HC7 are both high-gain tubes. Pentode sections in both tubes feature large gains, allowing good sensitivity. The diodes sections in both tubes offer solid detection and AGC stages for use in television receivers.