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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: Just outta curiosity posted by FenderLover on October 19, 2012 at 21:29:39:
RCA did a lot of the early tube development and first used 5V for tubes that were made to be run on 6.3V batteries. Radios used filament rheostats which were adjusted as the battery voltage dropped, to get the last bit of power out of the battery before recharging. Lots of people didn't have AC power yet, so would have had to take the battery to a garage (or hook it up to the tractor!)
When they developed AC tubes, they used 2.5V for minimum hum. Since power tubes and rectifiers used a lot of heater power, they used higher voltages - 5V, 7.5V - they were run on separate heater windings anyway. Early higher power transmitting tubes were 10V. The multiples of 2.5V made it easy to get the voltages right - 2, 3, 4 times as many turns on the transformer.
Meanwhile, Philco was making car radios that ran on 6.3V, so naturally they used 6.3V tubes. They bought tubes from Sylvania, not the enemy (RCA). 6.3V tubes worked fine on AC as well, so they had fewer tubes to stock. The 84 and 6X4 rectifiers ran on 6.3V and had insulated cathodes so that there was no need for a separate heater winding - but were only good for 70 mA and were prone to shorting... a problem Zenith collectors know well. Lots of '30s Zenith sets died when a 6X5 shorted and took out the power transformer. Some got repaired with a different transformer and 5Y3 or 5U4.
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Follow Ups
- RE: Just outta curiosity - Tom Bavis 10/21/1208:49:00 10/21/12 (1)
- Interersting, thanks! - FenderLover 15:28:35 10/22/12 (0)
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