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Re: cathode stripping

Posted by Doc B. (M) on March 7, 2007 at 08:19:32

In Reply to: Re: cathode stripping posted by DHT 4 ME on March 6, 2007 at 18:43:37:

I just wanted to mention the topic to cover all the bases. Is it a potentially bigger influence on shortening tube life than burning tubes 24/7? I don't know. My hunch is running tubes hard is the #1 life shortener.

You are right that our amps don't use a start up delay. That's because kit price is always an issue. Adding a delay circuit would increase price and complexity, and it doesn't seem that we have any problems with tube life. So we leave delay circuitry out. The driver tubes are not expensive and we don't hear much about replacement tubes, so it seems like a reasonable choice. If I was building something for myself that uses spendy tubes I might implement a startup delay - or at least a manual standby switch.

ARC tubes went fast possibly because they have had a rep for running them very hard, at least in their early designs.

I tend to agree with your hunch, that it's a cap related thing. Maybe you rig in a switchable load for the circuit that replaces the tube load to keep everything polarized when the tubes are off? How about a timer that switches the preamp on five hours before you begin to listen? A phone operated remote? ;^)>

Have you tried 6C45pis? I have found them to be a little more pleasant than the 417A (a little more 437A-like, speaking of $$$ tubes), and somewhat cheaper. 417s always sound a little white-ish to me, even run low and hot. If you stick with the 417s try some Raytheon 5842s. Seems like a lot of folks liked them over WEs when folks were playing with them back in the joelist days.

Oh yeah, loving the VDH. It's on a SME 309 mounted on one of Mike Paschetto's refurbed Empire 208s. Using 4722s for stepups. I'm just getting ready to put together my own new phono pre similar to the tape head repro amp - EF86 direct coupled to 7308 thru a passive RIAA, C4S loads for PS isolation, hybrid tube shunt regulation, Teflon output caps - and no BGs!

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