To: | amps@contesting.com |
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Subject: | Re: [Amps] 4CX1600B |
From: | "Ian White, G3SEK" <G3SEK@ifwtech.co.uk> |
Reply-to: | "Ian White, G3SEK" <g3sek@ifwtech.co.uk> |
Date: | Wed, 12 Nov 2003 09:09:49 +0000 |
List-post: | <mailto:amps@contesting.com> |
R. Measures wrote:
That would be interesting, but not necessary. Let's be logical about this. KL7RA has already told us what happened to this tube: the negative grid bias failed, so it pulled lots of current. The tube itself did not cause the fault. The question is whether the tube was damaged *by* the fault. This was a totally DC-related fault with a DC-related explanation. So why are we now diverting/confusing ourselves by thinking about the RF part of the amplifier? When the bias supply was repaired and the tube was replaced, the amp produced RF again as normal. Since nothing RF-related is broken, it don't need fixin' Also there is no logical reason to assume an arc here. That large pulse of current was quite probably normal electron current from the cathode, simply because the grid bias had failed. An arc is a different way of pulling lots of current, involving positive ions as well as electrons. Arcs in tubes sometimes do happen, but this time we have no reason to suppose that an arc took place. The bang would have come from the external circuit, where that same large current was also flowing (for example from a fuse blowing). So the only *relevant* question is whether that pulse of current has damaged the tube... possibly by pulling too many electrons from the oxide cathode surface. The only way to find out is to put the tube back in the amp and try it. Given the cost and difficulty of finding another spare 4CX1600B, don't let a few screws get in the way.
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