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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 26th November 2007, 07:56 PM   #11
smbrown is offline smbrown  United States
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Johnny, you put 400v on the plate of a 45? What current are you running at? My data sheet says max plate voltage is 275. As for output transofmers, I'd add that I've tried James, AN, Bartolucci (C core) and ElectraPrint all in conventional air gap designs. Of those, the James has been the favorite, second was AN. But, I'd really encourage exploring the parafeed design where both the choke and the output can be optimized for the tube. Or better yet, use a CCS in place of the choke and then into an optimized OPT (see Gary Pimm's site for more on this).
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Old 26th November 2007, 08:47 PM   #12
kmtang is offline kmtang  Canada
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Oppss.. sorry , my mistake. it should be 300Vdc.

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Old 26th November 2007, 11:05 PM   #13
arnoldc is offline arnoldc  Philippines
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Chris, you'll get tons of opinions in forums like this, which is a good thing, sometimes confusing.

I can even say try my 45 with grid choke and Tamura OPT for a different flavor, but hey, I'm digressing.

To answer your question about the JE Labs Simple 45 only, as I haven't heard a tubelab 45 yet...

The JE Labs Simple 45 sounds good, I have built it among other JE Labs designs - SRPP 2A3, 300B DX, 2A3 DX. Heck, I even had a Gordon Rankin 45 at one point, and I would say it beats the JE Labs Simple 45, in my room, with my gears.

But knowing DIY and based on your background, you may soon outgrow the JE Labs Simple 45. I myself ventured with my own brew and a favorite driver is 417A, which tubelab uses. If I were in your position and I would base my decision on the driver selection, I'd go for tubelab. I'm biased, it shows


There was a post prior that said James OPT tested poorly... I use James JS6113HS and I can say it does not sound poor, in fact it sound GREAT for the price I paid. From someone coming from a MagneQuest DS-025 and Tamura F-475 experience
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Old 27th November 2007, 03:05 AM   #14
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I have an obviously biased opinion here, so I just want to highlight a couple of things.

When I designed the TubelabSE, I spent a great deal of time optimizing the circuitry. The 5842 operates into a nearly ideal load under both the DC and AC conditions. The 45 is driven from a very low impedance source, and all filaments run on DC. That is why the "Tube Lab is rather more complicated than it needs to be." I wasn't trying to design a simple amp, that came later. These "complications" become more evident if the amp is operated near maximum power.

I built several of the popular 45 amps before I designed the TubelabSE. Most had some shortcommings. What is wrong with the direct coupled 45 amp mentioned previously? Think about what happens on power up. The tubes are cold, the solid state power supply brings up the B+ instantly. The CCS has no load yet because the driver tube is still cold, so its output voltage rails, puting a high positive voltage on the grid of the 45. The 45 warms up far faster than the driver tube, so as it begins to warm up, it is slammed into full conduction until the driver tube warms up. If you are going to build this design, use a 5AR4 to delay the startup somewhat.

Ignoring all of the above, the two designs use two totally different construction methods. The TubelabSE is built on a PC board. You assemble the PC board, connect 3 transformers, a choke, and the volume control to the PC board, and mount it all in a suitable enclosure. The PC board is quiet enough so there is no hum even on 106db speakers. Point to point construction requires careful attention to grounding to avoid hum.
Tubelab, it's 5 year mission. To explore strange new tubes, to seek out new circuits and topologies, to boldly go where no tube has gone before......
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Old 27th November 2007, 04:15 AM   #15
rickl is offline rickl  United States
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I haven't built or heard either amp but my vote is for tubelabSE. His helpful posts are worth something.

searching for jazz and a little libations.
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