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Post by Chilly Gibbons (Todd T.) on Nov 6, 2017 18:05:14 GMT -7
This may already have been discussed, but does anyone know how the half power circuit works? Does it cut the B+ to two of the tubes, leaving two at full operating voltage? If so, should we move the output tubes around if we usually play at 20W so the tubes wear more evenly? Thanks!
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Post by JasonM on Nov 6, 2017 19:15:23 GMT -7
I don't know the technical specifics and others will probably chime in but here is what I have read before on the subject:
"Without going into the details of the circuit and maybe revealing trade secrets, and again, as I remember it being explained to me. The 2 and 4 tube reference in the Z description refers to the "signal" from the tube, not what the tube is doing. All four tubes are functioning normally putting out "signal" all the time. At full power the "signal" from all four is reaching output. At half power the "signal" from two of the tubes is being diverted from output after they do their thing but before it gets to output." -headshrinker (Marc)
Thanks for the info folks and Dr Z!
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Post by premiumplus (Dave) on Nov 6, 2017 20:12:22 GMT -7
I'm pretty sure that the grid drive is removed from the two unused tubes at half power, so although they have heater and high plate/screen voltage applied, the plates (and therefore the tubes) aren't driving the output transformer and speaker in half power mode. If that's true, they are not wearing as much as the two other tubes that are doing the work. I'm going to swap my tubes every dozen or so of hours that I use the amp in half power mode. I think they're paired V7 & V9, and V8 & V10.
Doc, can you shed some light on this without revealing trade secrets?
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Post by headshrinker (Marc) on Nov 6, 2017 21:13:46 GMT -7
I'm the guy who wrote what Jason above quoted. I got what is going on from Doc and that was/is my way of saying what is going on without revealing something that he may not want revealed. It's his to reveal or not. He told me they were all wearing at the same rate, since I also asked him if I should rotate them. At least that's how I remember it. I'm old, who knows, maybe I hallucinated it. Have to add that at the time we were talking about the Remedy with which the the then JAZ now Z-Lux shares the same, maybe now similar, power section.
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Post by DRZ on Nov 7, 2017 5:07:08 GMT -7
I do not recommend swapping your 6V6's positions in the Z Lux. More damage can happen from improper handling , then uneven ware in my 1/2 power circuit design.
Z
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Post by doctorice on Nov 7, 2017 6:45:01 GMT -7
Quoting Dr Z in the Nov. 2017 Tone Quest Report:
"What I did was figure out a way to keep the four tubes working, but just not putting signal to two of them. If you took a scope and a meter and you put a test signal into it you would measure 10 volts AC peak to peak. If you switch to half power it will measure 5 volts exactly."
Doc provides a good description before the quoted material above about the "history" of pulling tubes to lower amp output and having to adjust the load.
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Post by Chilly Gibbons (Todd T.) on Nov 7, 2017 15:44:56 GMT -7
Thanks weighing in Doc. Sounds like uneven tube wear is not an issue. Now if you all will excuse me I have some noodling to do!
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