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Author Topic: Gi7B and GI46B Plate Voltage Limits  (Read 7184 times)
KO4NR
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Posts: 163




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« on: April 14, 2011, 11:56:20 AM »

I have seen amplifier designs around the Gi7B and GI46B tubes with Plate voltages exceeding the posted maximum limit of around 2000vdc.  Am I missing something or can those tubes be used without harm at those voltages?

73,
Bill
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VR2AX
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Posts: 758




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« Reply #1 on: April 14, 2011, 03:53:20 PM »

Maximum continuous plate voltage for the GI-7B (and GI-7BT which has a more robust node) is 2500 volts, although the tube was designed for pulsed microwave operation at up to 9KV.

http://www.radars.me.uk/gi7bt.htm

The GI-46B is basically a GI-7B with a more robust grid (20 watts grid dissipation instead of 7 watts).

For linear operation, maximum plate voltage is usually set round 2300-2600 volts, although some designs use up to 3000 volts. More conservative designs set the plate voltage around 2000 volts. At around 2400 volts you will need a fairly high bias voltage (around 30 volts) to keep the standing current within limits of 100-120mA.

In practice, these tubes should be carefully gettered over an extended period before use to improve the vacuum and reduce the risk of arcing. A ood control board is also essential.
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KO4NR
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Posts: 163




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« Reply #2 on: April 14, 2011, 05:36:13 PM »

Good!!  My power supply produces a plate voltage of 2900vdc resting and 2500vdc with the amp keyed.  It is a voltage doubler circuit.  The transformer and power supply components were replaced in 2005.
73,
Bill
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