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In Reply to: cathode stripping posted by Doc B. on March 6, 2007 at 17:41:38:
Hey Dan How are you. How is the VDH treating you, gosh I miss that midrange. Good reading article, thanks. Yes I know that the b+ switching causes stripping especially in high current high voltage applications but If you think about it every solid state rectifier comes on instantly and is at literally full HT before the 1st 2 seconds of turn on and is applying full B+ before the tubes heat up. Even your amps do that and I have not heard anything about Bottlehead gear that is negative in any way at all. In all fairness there probably is a negative effect especially considering the fact that amps today need re-tubing more often than the vintage stuff with tube rectifiers. The ARC amps we sold in NY went through tubes like M&M's ( early Chineese tubes) while vintage stuff just kept going.
I just don't like burning up those WE tubes 24/7.
Damm why do they have to be so good and spendy. I have a suspicion it is the caps forming much like the dreaded Black Gate warmup you have experienced except on a smaller scale since it is a MC preamp and possibly the 417a is more revealing. First thing tomorrow I am pulling the bleeder resistors and see if the stored charge in the caps reduces the warmup. It worked when I built a mu-stage using SKZ Black Gates.
Bob
Follow Ups:
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!
Oh Yes a cell phone remote startup. Heck if the terrorists can rig bombs from cell phones why can't we fire up our systems from one.
I have some Raytheonsn some RCA gold pins and the WE 417a's. The WE ones are the quiet choice. The RCA 's are very good but I only have 3 of them vs 14 Raytheons.The switched load sounds like a nice idea too. I have to sort all the ideas out as there are too many all of a sudden. The more resolving the system gets the more fickle it gets. I had an issue a few weeks ago where I plugged in a TV in the next room and suddenly the system sounded better even though it was on a dedicated line. It turns out that there was nothing at all on the line before plugging in the TV. Somehow the line had some resonance and plugging in the TV took it away. I had thought I had found the next Tice clock in TV form. What an eye opener that was to home wiring.
Does that 208 sound better than the Oracle? I bet is has more drive and pace. Your DC EF86 project sounds exciting, should be real quiet and dynamic. The EF86 always had a nice ripe and energetic sound in the circuits I heard it in like the Quad 2.
The Analog Engineering 208 is better than the Oracle and perhaps more interesting, it may be better than Mike's own The Turntable design. Very punchy and lively, and really tight on the bottom. This combo has been the first that has ever really satisfied me for vinyl listening, and I'm old and gray and been doing this since my first TD124 at the age of sixteen.The EF86 DC preamp is interesting. We tried the design years ago as a candidate for the Seduction design, with a very simple CRC PS. It didn't cut the mustard (too flabby) and the prototype sat gathering dust. A while ago I found out that the proto had been converted to gaseous shunt regulation by Ed Fallon and when I heard it again it showed promise. So PJ further evolved the design with dual mono actively loaded hybrid shunt regs and some other stuff and I made a tape repro amp with the circuit. It turned out to be a really good tape repro amp, and so the next iteration will be an RIAA amp.
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