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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: can I connect mixed tube heaters in series? posted by jarthel on August 10, 2006 at 20:01:56:
first, as Door Nail has pointed out, the tubes draw different currents, so that is out.Second, unless the tubes are designed for a controlled turn-on, they may heat up at different rates, which means that one tube may be over-voltaged during warm-up whereas another tube may be under-voltaged. In other words if one tube heats up quickly its resistance may increase faster than the other tubes, which means it will tend to have too high a voltage across it during warm-up. There are tubes which are designed to be used in a series heater string, for example the 6SN7GTB, where the B suffix refers to the fact that the tube is designed to have a slow warm-up characteristic to prevent this problem. In addition, these tubes are designed to have a fairly close tolerance on heater resistance when warmed up. Tubes that are not designed to have a specific warm heater resistance may vary more, resulting in variations in the voltage across a given heater when in a series string. In the absence of these specific design feature, connecting heaters in series is not the best idea for long tube life. Much better to run the tubes in parallel with the designed heater voltage.
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Follow Ups
- No, for two reasons.... - JimL 08:04:24 08/11/06 (2)
- Re: No, for two reasons - or maybe yes - Rob Mercure 10:53:08 08/11/06 (1)
- Re: No, for two reasons - or maybe yes - JimL 15:24:08 08/11/06 (0)
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