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Thread: JJ6V6

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    Member uneumann's Avatar
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    JJ6V6

    This is a new thread about an old topic. The JJ6V6 tubes seem to surprise (mostly good) in terms of performance. An earlier/related thread is at OK New issue with JJ tubes!. My question is about reliability and peak currents I'm measuring from this tube.

    The pp stage has the following params - which are not extreme compared to what others have described with JJ6V6s.
    CT B+ = 450V
    Screens = 350V
    OT Primary = 6.6k

    With an 8 ohm resistor load on the 4 ohm OT tap I get 23w (~clean) and I measure ~225ma peaks from each tube when Va drops to ~50V.
    I've seen other 6V6 amps with only about 100-120ma peak currents, so I'm a bit surprised and uncomfortable since 225ma is literally off all the tube charts I've seen and well beyond any Max Ia spec I've seen.

    Does anyone have experience with Ia current peaks like this and 6V6 reliability?
    This amp has played for about 10-15 hrs so far without noticeable problems - but current performance is no guarantee ....

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    I am not a technician or engineer or anything of the sort. So, this is all an educated guess on my part. I wonder if the JJ 6V6S was another "military" tube that was found to work well in a 6V6 circuit? I don't know when it was designed, but given that the factory is in a former communist country...

    I don't see it as a reissue 6V6 or anything of the sort; I see them like I see Sovtek 5881WXTs - cheap, sturdy tubes that take a lot of punishment. I like that they won't stress the heater winding like a 6L6 but they take crazy (for a 6V6) voltages. I would ask if you're willing to torture-test them, go for it & let us know what you find! I'm sure they have tested the parameters on their data sheets, but verification doesn't hurt.

    I'll leave it to the experts for anything else.

    Justin

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    Supporting Member mozz's Avatar
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    Does it sound really really good? If it does, it is right before it's gonna blow up. What wattage is the tube dissipating? What happens when you run the proper ohmage?

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    Member uneumann's Avatar
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    Quote Originally Posted by mozz View Post
    Does it sound really really good? If it does, it is right before it's gonna blow up. What wattage is the tube dissipating? What happens when you run the proper ohmage?
    Yes - I like it a lot - it's super clean and stays that way to pretty high levels - even w/o NFB.
    Amps that sound good AND blow up are what I'm trying to avoid.
    Fixed bias is at ~23ma, so ~9-10w per anode.

    I lowered the screen voltage to 350V after burning up some EH6V6s with 400V screens. With lower screens I had to raise the primary impedance to get the load line hitting the knee. Without any curves to work with, it's an incremental hunt to get all the parameters right. It came together with an 8 ohm load on the 4 ohm tap. 8 ohms on the 8 ohm tap cuts power a lot and sounds flat.

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    Bent Member Chuck H's Avatar
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    Stan (KM6XZ, ham call sign) our resident tube vendor has eluded to the idea that many currently available tubes defy the original parameters for their specs. He even suggested that such tubes should be either reassigned or, since models come and go frequently, simply handled in batches as tested for specs and sold as such. That is, the 6V6's in question AREN'T 6V6's, but still very valid tubes that, if the proper specs are known, could be put to their best use. Certainly they are "similar" to 6V6's, but so are 6L6's at face value and the two are practically interchangeable in some amps. So the JJ 6V6 would be a tweener tube. At least that's my take from all I've read for the last decade or more. Tougher than a 6V6, which is really good because there are a lot of vintage amps that abused average 6V6's before mains voltages increased, but probably not quite a 6L6.?. Anyway... I'm with Stan. There are some good tubes out there but you can throw the designators off a bridge. Very few of the Rusky tubes perform as per the original parameters for their model designators. Some are lower in performance and some are greater. Neither is a good thing because 1) we lack accurate data sheets to base designs on, and 2) if the original specs aren't recognized, how can we know what we'll get in the future? From a design perspective this is a problem. Adhering to the original spec sheets would instill more confidence in future product consistency and availability IMHO.

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    And by "adhering to the original spec sheets," we DON'T mean "chopping off the original company letterhead and substituting your own!"
    Yeah, I'm looking at YOU, EH /TS/Mullard/Gold Lion/whoever else that Big Conglomerate decides to gobble up! Do your own ding-dang-doodly -diddly research!

    Justin

    PS: I was just trying to say what Chuck said... Thanks!

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    Old Timer J M Fahey's Avatar
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    Stan (KM6XZ, ham call sign) our resident tube vendor
    I think you are mixing Stan with Yuriy, who is the actual Russian Tube vendor.
    As in: http://music-electronics-forum.com/t41244/ and elsewhere.

    Stan has (strong) opinions on tubes, like on many other subjects, but is not a tube vendor in the US market (he has sold some own brand Chinese ones in the Russian market but thatīs something else).

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    Juan Manuel Fahey

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    Bent Member Chuck H's Avatar
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    Yes, Yuriy sends me the updated lists. Mostly NOS stuff, so, actually matches the data sheets. But Stan is (or was) a vendor of modern tubes, knows A LOT about the current Rusky production and distribution and I really don't think he's wrong in his opinion AT LEAST about some modern tubes being just fine, but NOT matching their golden age model designators.

    Of course I can't blame anyone for raising up Yuriy and pushing down Stan. They've both earned it

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    Member uneumann's Avatar
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    Quote Originally Posted by Chuck H View Post
    Stan (KM6XZ, ham call sign) ... That is, the 6V6's in question AREN'T 6V6's, but still very valid tubes that, if the proper specs are known, could be put to their best use. ... Tougher than a 6V6, which is really good because there are a lot of vintage amps that abused average 6V6's before mains voltages increased, but probably not quite a 6L6.?. ... 1) we lack accurate data sheets to base designs on, and 2) if the original specs aren't recognized, how can we know what we'll get in the future? From a design perspective this is a problem. Adhering to the original spec sheets would instill more confidence in future product consistency and availability IMHO.
    Thanks for the situation summary. Your conclusions make sense if I were producing/selling a product. However, I have this beast built now and I hoped that by now people would have some history with this bottle and perhaps some better design info (curves etc). If it exists somewhere, I'm calling for sharing it.

    Based on my measurements in this design I scaled the old 6V6GT curves to fit... well sort of fit, the bias point and the peak current point. This is crude - but I lack a curve tracer. It is a likely first-order approximation and does illustrate how different the tube behaves from a 6V6 or 6L6. The Iso power curve is not really meaningful since we don't know the real power limits of the tube. It's just a reference for ~20w dissipation, which is over "spec".

    Click image for larger version. 

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    Don't forget the joker g1's Avatar
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    How does it look against an authentic NOS 5881 spec.?

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    Bent Member Chuck H's Avatar
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    Well the JJ6v6 does have a spec sheet that doesn't simply ape the vintage spec sheets. It may be one of the only newer tubes with different characteristics from the old model numbers that does. It's somewhat limited and I can't account for it's accuracy, but here it is.

    http://www.drtube.nl/datasheets/6v6s-jj2004.pdf

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    Member uneumann's Avatar
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    Quote Originally Posted by Chuck H View Post
    Well the JJ6v6 does have a spec sheet that doesn't simply ape the vintage spec sheets. It may be one of the only newer tubes with different characteristics from the old model numbers that does. It's somewhat limited and I can't account for it's accuracy, but here it is.

    http://www.drtube.nl/datasheets/6v6s-jj2004.pdf
    Right - I've looked at that sheet. Can't tell much that's useful since it looks like they only plotted triode curves. (Or am I missing something?) The other specs are also pretty sparse and seem to just confirm that the tube will tolerate about the same conditions (a bit more perhaps) than the 6V6GT.

    The lack of pentode curves means there are no plate and screen characteristics to design around. We also don't know what the true limits are. Other 6V6 curves are way different and essentially useless (I tried using them) since a design load line could completely miss the intended/expected curve knee (by a lot in my case). This is probably why some people report getting less power from their amps using this tube even though it's rated for higher power. All of this gets back to your point that it's a tube that's available to try, but it's a crap shoot to design around.

    That said - there are lots of these tubes in use and they seem to occupy a nice space between the 6V6 and 6L6. If anyone out there has a curve tracer - a lot of people (especially me) would appreciate it if you could run and post a few pentode curves at varied screen voltages. Even curves from just one tube would be something to work from and reference for comparisons.

    If, as you say, there is a trend for new tubes straying farther from how they're labeled, the need for measuring and posting data becomes more important. Would a tube vendor gain some cred and advantage for taking the trouble to post some typical curves for known outlier tubes? A vendor can't guarantee a tube you buy will meet those curves, but that's no different than the situation we have now. Maybe I'm just wishing for too much...

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    Member uneumann's Avatar
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    Quote Originally Posted by g1 View Post
    How does it look against an authentic NOS 5881 spec.?
    Looking at the TungSol 5881 data sheet, it seems the 5881 is higher power (more plate current at similar plate/screen voltages) than the JJ. But it also reinforces the description of the JJ as somewhere between a 6V6 and 5881/6L6. Makes one wonder if the manufacturer cooked up this new tube intentionally or whether it was a design that went wrong and they salvaged it by calling it a 6V6.

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    Better Tone thru Mathematics bob p's Avatar
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    Chuck brings up a very important point -- what just about everyone is selling today as a 6V6 isn't actually a 6V6 and it never has been. It's always been a Comm-Bloc "close enough" tube that has been used successfully in 6V6 applications, so that's how the tube vendors are marketing that product. All of the Comm-Block producers have been manufacturing tubes to the Eastern/Central European specs -- if they're even able to build to those specs today. They are not, nor have they ever been, producing genuine Western-spec tubes. The best that we can hope for today is a reasonable substitute, not the real thing. In that context it's no surprise that even the best 6V6 from JJ don't sound like a real RCA 6V6. The reality is that the tone legacy is becoming lost.

    The MI industry is populated by shifty types who will acquire the trademarks of the defunct Western tube manufacturers and slap those labels on these Central/Eastern European products, calling them something they aren't. I don't have a problem with that -- they're doing what they can to provide a product in a market that wants to buy what they're offering. What I do take issue with though, is their use of recycled old tube data sheets, applying them to these new products as if the old data sheets could even apply to the new products. They can't because the underlying device is different.

    What the new producers and new vendors should be doing is to provide new data sheets that accurately reflect the performance of their products. But they're not doing that, for a couple of reasons. First, accurate data sheets might reveal that the category of tubes being sold aren't the equivalent of the tubes that they're being sold as. Today the Russian product that's being sold as a 6L6GC might not meet the specs on the GE 6L6GC data sheet. Second, with accurate data sheets it may become evident that the new production tube that they're selling isn't even close to meeting the performance of the old Comm-Bloc tube that it's actually based upon.

    If a vendor doesn't provide accurate data sheets, there's a reason for it.

    In the big scheme of things I think it's important not to trust the tubes that are being sold today as being equivalent to NOS. going further, I don't even trust them to be what the label says they are. The reality is that the manufacturers refuse to provide reliable data on current production tubes. If you use them then you're on your own to determine the tubes performance limits and not to stray outside of those boundaries. It sucks.

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    Supporting Member mozz's Avatar
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    It's a 6v6S, not a 6v6. I think i remember them drawing a little more filament current. One would need to look at older Russian tube datasheets and see if something had hot 6v6 specs, chances are they just changed the pinout.

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    Bent Member Chuck H's Avatar
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    I did a little peek around and only found a lower spec 6v6 equivalent in the old Rusky products. My understanding is that a lot of the old model designators are being made on equipment salvaged or bought cheap from many of the western Euro factories. So why change dies and forms and such? Sorry I can't recall my sources as my memory is reaching back to a prior epoch for this So fact check as you like. I'm usually willing to be wrong.

    Of course this doesn't preclude the possibility that the tube inside the 6v6s bottle was once in a completely different Russian bottle with an entirely different base. This doesn't seem like a stretch.

    Looking at old black and white footage from the golden age it's clear that there was a tremendous amount of QC and skilled labor at the factory level that I've read simply doesn't exist today. So the old dies and stamps for, say, el34's of one type or another may be in use, but the tubes don't perform the same due to tolerance and materials. I think some of us have seen a lot of this sort of thing. You know, brand new el34's with regurgitated spec sheets that say the plates can take 800V shorting to the heater at 470V during clipping with all other specs observed.

    From what I gather most of the 6L6 types perform as expected. El34 types are a weak link, as are 6550's and the uber kt types. The kt66 aren't "real" kt66's but still function, as with 6v6 types. The strongest performers for tone AND function seem to be a couple of the 6l6 types, one of the 5881's and a couple of the el84's (just look at what the Carr, Bruno, Fuch's, etc are using). As for el34's, well... We're not going to go on without them, so just use the Ruby selected Shuguang tubes labeled el34b. Try to keep it limited to heads because IMHE they tend to microphony, but otherwise sound and perform well. I use mostly el84's and I'm getting the most joy from the 6n14n/6p14p types with the longevity and or durability suffix codes like EM or K. Most are from the old Reflektor factory. I have about 20 K's right now. They are ruggedized and tested for microphonics. Since my own personal amp is a combo and these tubes are lasting easily three times as long as market versions and sounding great, I am pleased.

    These are my limited observations and experiences on the matter.

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    JJ6V6S Curve Traces

    Quote Originally Posted by uneumann View Post
    That said - there are lots of these tubes in use and they seem to occupy a nice space between the 6V6 and 6L6. If anyone out there has a curve tracer - a lot of people (especially me) would appreciate it if you could run and post a few pentode curves at varied screen voltages. Even curves from just one tube would be something to work from and reference for comparisons.
    I fired up my uTracer and took the following readings of my JJ6V6S. Raw data also attached. The uTracer is limited to 400V and 200ma.

    Let me know if I can do additional readings to help.

    Solid lines = Ia, dashed =Is

    Vs = 250V
    Click image for larger version. 

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    Vs = 300V
    Click image for larger version. 

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    Vs = 350V
    Click image for larger version. 

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    Vg = 0, varying Vs
    Click image for larger version. 

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    Transfer Characteristics
    Click image for larger version. 

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    Tristan
    Attached Files Attached Files

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    Member uneumann's Avatar
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    Quote Originally Posted by tristanc View Post
    I fired up my uTracer and took the following readings of my JJ6V6S. Raw data also attached. The uTracer is limited to 400V and 200ma.

    Tristan
    Excellent! Thanks so much Tristan. They're all great and the Vg=0 curves are really useful to me right now.
    I was looking at the utracer page yesterday and thinking about building one ... what a great project.

    Edit - These curves ARE a good fit to the 6V6GT for the conditions in most spec sheets - except that screen current seems quite a bit higher that the Radiotron values, for example. (I don't think I'm misreading that.)
    My statement above about the JJ curves being different from other 6V6s is wrong - I was comparing two different operating conditions, so of course the curves differed. These curves DO cover my conditions better so they give me better insights into what's going on. The higher screen currents are something I'll consider more carefully.

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    Last edited by uneumann; 01-02-2018 at 12:06 AM.
    Old Tele man: Equations provide theoretical values, SPICE provides approximate values; but, the ears provide exact values.
    Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.

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    I really like the JJ6V6S as they stand up really well to the high voltages often found in amps that run 6V6 tubes. I have customer that have been running the same set of tubes professionally for three years at 480V. They're my go-to tubes for reliability. NOS tubes are ridiculously priced and for me as a repairman fitting NOS into an amp that's running high voltages is not good economically. I find that most NOS vendors are challenging to say the least when it comes to claiming under their flimsy warranties. Most disappear like cockroaches in a Mediterranean kitchen when the light is switched on.

    The one thing you would never know from a NOS tube is whether it was a return back in the day that's now found its way back into the system, or whether it's a clean-but-used repackaged 'pull'. At least buying a new tube carries some comfort. The JJ6V6 has been out long enough now for the dust to settle on whether its any good or not, and in general the answer is that it is a good tube. The argument whether its a true 6V6 or not doesn't bother me so long as it works as I expect. Some of my customers are super-picky and are fine with the JJ.

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    Quote Originally Posted by uneumann View Post
    Excellent! Thanks so much Tristan. They're all great and the Vg=0 curves are really useful to me right now.
    I was looking at the utracer page yesterday and thinking about building one ... what a great project.
    It is great and I'd highly recommend it - for me it was to satisfy my curiosity and help with understanding of the design process. I run it using a bench DC power supply and a few of Pete Millett's breadboard sockets and just re-wire as needed.

    I think it would be worth having an online repository of the dumped data files - a form where people could submit a file with the valve make, year etc etc. Could help with averaging and improved SPICE models. And also could be used to generate curves for particular operating conditions by interpolation and so on.

    Edit - These curves ARE a good fit to the 6V6GT for the conditions in most spec sheets - except that screen current seems quite a bit higher that the Radiotron values, for example. (I don't think I'm misreading that.)
    I checked against the GE 6V6GT data sheet: for ~100V on the anode I make 16mA on the screen at Vg=0, which compares to 18ish mA from the uTracer (are you reading right hand axis?).

    I've a couple of very old 6V6Gs - a Tungsram (England) and a GE (Canada) plus an unidentified one which rattles a lot. I could run the same tests when I have the time.

    T

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    Just a thought? Could the JJ6V6S be the same guts as their 7591?

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  22. #22
    Senior Member potatofarmer's Avatar
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    Quote Originally Posted by 1ampman View Post
    Just a thought? Could the JJ6V6S be the same guts as their 7591?
    I've always wondered this myself, but after seeing the uTracer curves, they're not passing anywhere near as much current as the 7591 datasheet shows. Possibly the same plate (and screen?) but with a different cathode, or at least a different heater as the JJ 6V6S heater has a rated draw of 500mA while their 7591 has a rated heater draw of 800mA.

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    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by tristanc View Post
    I fired up my uTracer and took the following readings of my JJ6V6S. Raw data also attached. The uTracer is limited to 400V and 200ma.

    Let me know if I can do additional readings to help.

    Solid lines = Ia, dashed =Is

    Tristan
    dude, this is AWESOME that you did this. I personally find graphical data, to be a huge design tool. Modern Manufacturers don't seem to publish much in the way of new curves on current production tubes, which I find frustrating sometimes.

    Richard Kuehnel gives a helpful way of plotting fairly accurate new plate currents (Ip2) based on published plate currents (Ip1) for a given screen voltage, if the desired screen voltage (Vs2) is close to the published value (Vs1).
    **it's easier for me to show you like this, so I don't screw it up trying to translate it clearly into text**

    in "Guitar Amplifier Power Amps", he describes it as follows:
    "In these formulas Vg is the grid voltage for which the plate current is being estimated and Vgc is the grid voltage where the tube goes into cutoff when operated at the published screen voltage"

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    Quote Originally Posted by tristanc View Post
    I fired up my uTracer and took the following readings of my JJ6V6S. Raw data also attached. The uTracer is limited to 400V and 200ma.

    Let me know if I can do additional readings to help.

    Solid lines = Ia, dashed =Is

    Vs = 250V

    Vs = 300V

    Vs = 350V

    Vg = 0, varying Vs

    Transfer Characteristics

    Tristan
    Thanks for posting those traces, very interesting. Any additional traces you care to make would be greatly appreciated.
    I'd like to be able to open your zip file, but I can't seem to be able to open .utd files; could you pack them in another format?

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    Last edited by Bendyha; 01-05-2018 at 09:50 PM.

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    Quote Originally Posted by Bendyha View Post
    Thanks for posting those traces, very interesting. Any additional traces you care to make would be greatly appreciated.
    I'd like to be able to open your zip file, but I can't seem to be able to open .utd files; could you pack them in another format?
    What values would you like?

    The .utd files are just text files, so you can rename them to .txt.

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    Better Tone thru Mathematics bob p's Avatar
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    years ago i had thought about building that tube tracer, but with the 400V limit I can't take it seriously.

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    "Stand back, I'm holding a calculator." - chinrest

    "I happen to have an original 1955 Stratocaster! The neck and body have been replaced with top quality Warmoth parts, I upgraded the hardware and put in custom, hand wound pickups. It's fabulous. There's nothing like that vintage tone or owning an original." - Chuck H

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    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by bob p View Post
    years ago i had thought about building that tube tracer, but with the 400V limit I can't take it seriously.
    That doesnt bother me so much. I just wish it was designed to drive the grids positive.

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    Better Tone thru Mathematics bob p's Avatar
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    I guess it depends on what you want to use it for. If you're just screening preamp tubes it's no big deal, it'd work fine. But if you're trying to create a composite load line diagram for a pair of push pull power tubes, it can't even give you a single set of curves at real world working voltages.

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    "Stand back, I'm holding a calculator." - chinrest

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    Senior Member SoulFetish's Avatar
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    I get it. 500V would be better, but do you really need anything higher than that?

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    Better Tone thru Mathematics bob p's Avatar
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    I've got lots of amps that run over 500V B+.

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    Have any of you guys who are looking for tube tracers heard of the etracer? Its a facebook group for a tracer this guy made that works with a computer I believe. I haven't had the time to delve into it a lot but it looks interesting.

    Greg

    facebook group site
    https://www.facebook.com/groups/154835195049377/

    parent site
    http://www.essues.com/etracer

    downloads link
    http://www.essues.com/etracer/index.php/downloads

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    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by soundmasterg View Post
    Have any of you guys who are looking for tube tracers heard of the etracer? Its a facebook group for a tracer this guy made that works with a computer I believe. I haven't had the time to delve into it a lot but it looks interesting.

    Greg

    facebook group site
    https://www.facebook.com/groups/154835195049377/

    parent site
    http://www.essues.com/etracer

    downloads link
    http://www.essues.com/etracer/index.php/downloads

    Thanks for the heads up! I wasn't aware of this project, but it looks like there are some promising developments.
    Still though, am I the only one interested in featuring a low impedance grid drive to plot operating curves for positive grid voltages??

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