interesting... can you give some more details? How did you wire the hexode grids?
There´s been some talk about EL156 earlier in this thread. MJK´s design together with this tube could be a real winner. Indications of 20W Pout, low THD and dominating 2nd order all the way up to just before clipping. 5k load, 450V Ua(525V B+), 100mA Ia and 280V Us. Must try, but maybe with a little more safety-margin!
As it was pointed out to me if you remove the space between Simple and SE in the term Simple SE, you have a trademark that belongs to a solid state HT box that is neither simple or SE!
If it is the PTO doesn't know about it.
There have been a lot of things called "6BQ6" over the years. Some can not handle much more than 12 watts while some can deal with much more. Again the real maximum G2 voltage varies with the individual tube construction. You will need to explore the limits of the actual tubes that you intend to use. Some of this was pointed out here:
http://www.diyaudio.com/forums/tubes-valves/160783-6av5ga-amp.html?highlight=6bq6ga
It has been stated by others that the 6BQ6 types work great in P-P but the linearity in SE use isn't so great. I tend to agree. In many cases the point where the best performance occurs in into the "red zone". I tweaked a pair for optimum performance in a Simple SE board and they were running a wee bit hot.
I didn't. G2 and G4 are internally connected inside the tube. The 7 pin tubes all have a similar and compatible pinout if you have pins 2 and 7 connected together at the socket. This is the case with Petes red board. See post # 145 for my list of compatible tubes. There are more, those are just the ones that I have.
http://www.diyaudio.com/forums/tubes-valves/151206-posted-new-p-p-power-amp-design.html
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Can you please provide a reference? It sounds like you are in defense of IP mode...
"If the goal is not to achieve the absolute maximum watts but to build a “Cheap Basic SET” can we push the plate voltage (also cathode current) of a triode-strapped pentode above the published 12 watts of a 6BQ6GTB?"
Is the reference to "Cheap Basic SET" in the above sentence pertaining specifically to your trademark, or is it a generic reference? Trademark holders usually take more care in the public use of their mark ;-)
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The reason for the 01N100 is mainly that it's my go-to depletion FET these days
datasheet shows it as n-ch enhancement
The IXTP01N100D is a relatively new 1000V depletion mode device from IXYS. I abberviated the part number on the schematic to make things more legible...
It's an excellent part, very low capacitance Crss=5pf. Also has a higher Vth than the others which is nice sometimes.
Since the datasheet has no curves, I measured one myself.
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Busting the Pd= 12W spec is definitely do-able. I have a 6BQ6GTB project that runs Class AB1, PP 6BQ6GTBs at Pd= 17.5W with no visible color on the plates. 6BQ6GAs also work in that project, bias up the same, and mey be sound a bit better. Watch out for those 6BQ6GTAs, however, as these red plate.
Also, the Sylvania black plate 6BQ6GTBs can take some 70mA of cathode current at Vpp= 350Vdc without showing any color. The RCA gray plates will show just a trace of color at that cathode current.
That Pd= 12W spec is highly conservative for an application that runs max RMS power continuously. Audio is much less demanding.
That's some advice that needs to be taken with a grain of salt. Tubes like the 6BQ6 place the screen very close to the cathode. Over volting the screen could lead to run-away, or arc-overs. It is something you may get away with, depending on tube type, manufacturer, and model. Then, again, you may not always get away with it.
“Simple SE” think Tubelab
“Simplistic” think Salas
“Cheap Basic SET” trademark is used in the less formal lower case DIY Forums sense.
A 6BQ6GTB “Cheap Basic SET” operating at 12 watts dissipation may produce 2 watts. I will build one, test it and post the results here.
DT
All just for fun!
“Simplistic” think Salas
“Cheap Basic SET” trademark is used in the less formal lower case DIY Forums sense.
A 6BQ6GTB “Cheap Basic SET” operating at 12 watts dissipation may produce 2 watts. I will build one, test it and post the results here.
DT
All just for fun!
Not that I can find with a PTO search. The word "Simple SE" without the space is a registered trademark of Nuvo Technology corp as used in the audio and Home Theater markets. They made it clear to me that I was not to use it and any misuse would be defended. The problems arrise when I and others left out the space between the common words or abbreviations Simple and SE in posts on this forum. I have asked that posters on this and other forums be careful using those words. Fortunately no lawyers were involved.
It seems that there are people who use Google to find unwanted users of their trademarks. Trademarking common words is very difficult especially after they have become generic. Consider the word "asprin". Bayer could not trademark it after it was in common use.
IIRC this depends a lot on the load and what you run the tube at. If you try to squeeze max output out of it then yes it has a lot of h3 but there are other loads that will produce a lot of h2 instead and hardly any higher harmonics. The KenRad paper comes to mind.
edit: having said this I've seen some reports that for SE use reckons the EL84 is a far better tube. But then in PP the 6L6GC can put out a lot more power than the EL84 can. As far as I know the 6L6 was designed for PP operation but I like it even in SE use which came about by having a quad of Tungsol 6L6GC-STR left over after selling a Chinese PP amp that had these tubes in them. Initially intended for upgrading I found apgrading that amp to a good performance would cost more than building one from scratch and selling the Chinese one: it would need new iron (mains TX underrated, OPT just not good enough, PSU left many things desired etc) Only thing left would be the volume pot, sockets and chassis.
AM
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there's something I do not understand here. According to some datasheet I've found, it's Va(max) is "only" 750V. How could you run it at 1050V?
There are some ham radio rigs that run these tubes at a lot higher voltage in SSB / CW mode (e.g. the Kenwood 520-530). It will shorten the life of the tube but not as much as one would think. Forced air cooling has a lot to do with it.
AM
Hey guys,
Why are you even mentioning 6BQ6 or 6L6 in a thread about linear triode-strapped pentodes? 6L6 works great as Schade but triodestrapped it sucks. 6BQ6 seems even worse but maybe Schade can help there too? SE or PP is not the subject. Only the linearity of the tube characteristics interests me.
The only one I´ve found so far is 813. 850V/5k as Millett uses looks OK when you check the curves. I´ve got four 813´s on the shelf waiting for the right chassis and OPTs.
http://www.pmillett.com/file_downloads/813%20curves.gif
Yet to find another an equal but lower power. Until then Schade rules.
Great thread anyway, with many interesting angles!
Why are you even mentioning 6BQ6 or 6L6 in a thread about linear triode-strapped pentodes? 6L6 works great as Schade but triodestrapped it sucks. 6BQ6 seems even worse but maybe Schade can help there too? SE or PP is not the subject. Only the linearity of the tube characteristics interests me.
The only one I´ve found so far is 813. 850V/5k as Millett uses looks OK when you check the curves. I´ve got four 813´s on the shelf waiting for the right chassis and OPTs.
http://www.pmillett.com/file_downloads/813%20curves.gif
Yet to find another an equal but lower power. Until then Schade rules.
Great thread anyway, with many interesting angles
!
We mentioned both actually.
12BQ6GTB in my amps with Schade work like a charm.
Also, I tried them with success as drivers (LTP) for Schaded Gu-50
EL156 looks like a winner. Load line below is pretty linear.
I would go with 4K plate load for 20W plate Po given 450V/100mA. Looks like 280V g2 is good scaling to 4K loadline also. The DCR of the OPT would be the determining factor for output resistance ;-) Tube only contributes 100 ohms effective Rp. 4K plate load would be 3K6 or 3K8 nominal plus DCR.
Point of reference: on my 5881WXT tester with 250V g2, the anode swing looks like it goes down to about 35V at clipping.
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Dang, I must be getting old. I have hundreds of these things, and several dozen 5915's (a dual control heptode with nice pentode curves) and I didn't even think to try them in the red board. Yes, the pinout is compatible and this might even give us a new place to connect the Schade resistor (choose a grid!). My red board is back on the shelf for now, but next time I have it hooked up I will stuff some 6BE6's and 5915's into it.
The thinkers can find all sorts of reasons why this won't work, but I would rather just try it. There are 3 possibilities, it doesn't work, it works, or smoke and fireworks happen. At least two of the three would be interesting!
SS Schadeode, A Linear "Triode"
Something I've wondered about that I now have the opportunity to test. Using the same testbed, I mocked up a SS version of a 6L6 using a low capacitance 1700V IGBT (6pf Crss) and a 200 ohm resistor in the source to limit the gm to about 5000 (200 ohms Rp effective, just like the 6L6 Schadeode I tested earlier).
I built it onto an octal plug so I can swap back and forth with only a change in feedback resistor to compensate for higher gate voltage of the MOSFET + Rs vs. grid voltage of the 6L6.
The distortion spectra are amazingly similar, with the SS version producing a little more 4th harmonic above 1W and a little less 3rd harmonic between 5 watts and clipping. Power output at clipping is the same 9W at the speaker terminals.
They also sound amazingly similar; the SS circuit is also neutral to slightly SET-like on vocals but with the same tight bass control and low end punch as the tube Schadeode.
Oops, forgot to show the gate protection zener on the IXGH6N170A. I included it from the start as it's probably needed; I don't want to find out...
Something I've wondered about that I now have the opportunity to test. Using the same testbed, I mocked up a SS version of a 6L6 using a low capacitance 1700V IGBT (6pf Crss) and a 200 ohm resistor in the source to limit the gm to about 5000 (200 ohms Rp effective, just like the 6L6 Schadeode I tested earlier).
I built it onto an octal plug so I can swap back and forth with only a change in feedback resistor to compensate for higher gate voltage of the MOSFET + Rs vs. grid voltage of the 6L6.
The distortion spectra are amazingly similar, with the SS version producing a little more 4th harmonic above 1W and a little less 3rd harmonic between 5 watts and clipping. Power output at clipping is the same 9W at the speaker terminals.
They also sound amazingly similar; the SS circuit is also neutral to slightly SET-like on vocals but with the same tight bass control and low end punch as the tube Schadeode.
Oops, forgot to show the gate protection zener on the IXGH6N170A. I included it from the start as it's probably needed; I don't want to find out...
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I wonder if a good portion of that is the fact you are using an output transformer with each version. Most transistor amps not requiring it...
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