Actually, it was a late design. The beam tetrode had already been invented and patented and companies like Mullard wanted a power tube they could market without paying royalties.
The 6L6 predates the EL34 by a long while - close to 20 years.
They happily run at well over 700 volts - well over the ratings for 6L6. They live for decades, literally decades running 500V on the plate at max Wdiss. They're reputation is only questionable in your eyes. Everyone else knows it's a fine, reliable design.
6L6 is a very old type with rather primitive specs that dates to the 30s. Yes, it got better over the years, they all did. Things like the 7591 and 6CA7 were much more sophisticated.
EL34 was purpose designed in the 1950s as an audio amplifier tube. It has all the right characteristics for the purpose that could be achieved at the time. Far more sophisticated than the (already old) 6L6. The American version was 6CA7 and was typically a beam tetrode, not a pentode. And it really depends on who produced it, whether it was better or not.
Prefer whichever tube you like, but try to do it for real reasons - the history of these things is interesting and involved enough without making things up and swapping decades around. The datasheets don't tell all, but really they aren't meaningless either.
Quote:
Originally Posted by nazaroo
...
Using SE output transformers (to ground) might also allow dropping the output caps.
...
So have you actually built the SE version of this?
Originally Posted by nazaroo
...
Using SE output transformers (to ground) might also allow dropping the output caps.
...
You're the one who suggested it. I was just asking how it would work.
So are you saying that the SE transformer can connect from B+ to the mu-follower output without a coupling cap?
Would you use resistors for the voltage divider network?
So have you actually built the SE version of this?
Back to front. Philips (of which Mullard were a part) had invented the pentode. Others wanted a similar valve they could market without paying royalties, so the beam or kinkless tetrode was invented and then given to RCA. So the US, plus MOV/GEC in the UK, developed tetrodes; 6L6 was an early one, closely folowed by the 807, later a baby version (6V6) came along and others to.Ronsonic said:
Meanwhile Europe, dominated by Philips, continued to develop the pentode through several generations and eventually the EL34 was born.
Hmmm,
Actually I find myself realizing that this little bit of tube (sorry DF96:..."valve"..) history is much more interesting than the topic of this thread....
Actually I find myself realizing that this little bit of tube (sorry DF96:..."valve"..) history is much more interesting than the topic of this thread....
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Good post, thanks for the history.
I have my se amp running el34s, it gets used for hours every day and my el34s are doing fine after several years.
Yes, I am also fascinated by the histories of valves.
I cannot justify the following statement but I do suspect that for a power valve the beam tetrode design is probably better than a pentode, and the fact that the final developments - at least for high-power and RF applications - in Europe were (apart from the triodes!) beam tetrodes - e.g. YL1070/1, QQVO7-50, YL 1150, QE08-200 and so on, suggests that Philips and others knew this too.
Paul
No need to translate - its not what I call it but I realise that to many others they are tubes!pieter t said:
Sadly, much of the history of these items is now probably lost. For example, there is nobody to ask why the ECC85 has higher heater current than the otherwise very similar ECC81, and why Mullard made misleading claims about it (e.g. higher input impedance, high gm).
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Did the later pentodes, like EL34, eventually adopt the aligned grids setup to lower screen current?
As far as the posted topic, it would be useful if someone could post an FFT of a class A P-P triode amp at near full rated power (at say 20 or 30 Hz test signal with a dummy speaker load) to see if the ripple sidebands are significant or not. (it may be difficult to resolve tiny sidebands so close to the main signal) (that OTHER Aikido thread went to 19 pages with no data posted, we've gotten to 11 pages here so far)
Seems that just putting a CCS under the power tube cathodes (or in the B+) would achieve the same PSRR isolation results (still class A) without all the extra inefficiency. And what value of resistance is used above the lower power tubes in this scheme? Can they effectively pull down the OT primary? ( the earliest schemo had the lower tubes directly connected to the primary ends, but the later ones have two resistors in series)
As far as the posted topic, it would be useful if someone could post an FFT of a class A P-P triode amp at near full rated power (at say 20 or 30 Hz test signal with a dummy speaker load) to see if the ripple sidebands are significant or not. (it may be difficult to resolve tiny sidebands so close to the main signal) (that OTHER Aikido thread went to 19 pages with no data posted, we've gotten to 11 pages here so far)
Seems that just putting a CCS under the power tube cathodes (or in the B+) would achieve the same PSRR isolation results (still class A) without all the extra inefficiency. And what value of resistance is used above the lower power tubes in this scheme? Can they effectively pull down the OT primary? ( the earliest schemo had the lower tubes directly connected to the primary ends, but the later ones have two resistors in series)
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Licensing?!
To me this thread was quite funny up to the point when the creator tells us that he is licensing the use of the mu follower to others. I will remember to ask next time i plan to use it 🙂
/Anders
To me this thread was quite funny up to the point when the creator tells us that he is licensing the use of the mu follower to others. I will remember to ask next time i plan to use it 🙂
/Anders
EL34 screen current is about 15% of anode current so I'm not sure. If it was 20% I would say definitely unaligned grids. 10% means probably aligned grids.
That's what the late Allen Wright did with his PP 300B amplifier, but not so much to improve PSRR.
The drawback of a CCS is the risk of hard clipping when the amp runs out of power. One of the benefits of tube amps (soft clipping) is gone then.
High efficiency loudspeakers are a must when using CCS loaded tube amps.
Beam and Kinkless tetrodes are very different things. Kinkless tetrodes are fair tetrodes, they do not have the 5'th element.
Wavebourn sent me some pentode GU50 tubes to curve trace, and the grids could be seen thru the slotted plate. The grid 1 and 2 appeared to have the same winding pitch and approximate alignment. There was some dissagreement online as to whether they were aligned. Usually the slotted plates are a good hint that alignment was done visually during construction.
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A Mu follower usually has significant resistance above the plate of the lower tube to get the impedance up. It is optimised more for the bottom tube to be the driver for the top tube, not as a P-P stage all in itself.
I would suggest that one of the "anti-triode" configurations would be better suited here (instead of Mu follower) for a stacked P-P output stage. This puts near equal low resistance (just enough for top tube biasing) resistors in series above the bottom tube plate, with the output taken from the mid point (between the resistors). The top tube then keeps the sum of the currents thru the two stacked current sense resistors approximately constant for optimum complementary P-P operation.
(ie, near constant voltage across the two resistors. A high gm depletion mode Mosfet up top would be even better, requiring little drive signal drop in the resistor and somewhat lower voltage B+. The bottom resistor is just a little higher Ohms to provide the gate or top grid drive signal. )
Seems that Tubecad/Broskie now calls this SRPP+: http://www.tubecad.com/2009/10/blog0174.htm
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A Mu follower usually has significant resistance above the plate of the lower tube to get the impedance up. It is optimised more for the bottom tube to be the driver for the top tube, not as a P-P stage all in itself.
I would suggest that one of the "anti-triode" configurations would be better suited here (instead of Mu follower) for a stacked P-P output stage. This puts near equal low resistance (just enough for top tube biasing) resistors in series above the bottom tube plate, with the output taken from the mid point (between the resistors). The top tube then keeps the sum of the currents thru the two stacked current sense resistors approximately constant for optimum complementary P-P operation.
(ie, near constant voltage across the two resistors. A high gm depletion mode Mosfet up top would be even better, requiring little drive signal drop in the resistor and somewhat lower voltage B+. The bottom resistor is just a little higher Ohms to provide the gate or top grid drive signal. )
Seems that Tubecad/Broskie now calls this SRPP+: http://www.tubecad.com/2009/10/blog0174.htm
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I feel responsible for starting this off topic discussion about EL34. It's not often one
hear bad things about EL34:s so when a guy like nazaroo mentioned this, I just have to
ask. I find it intresting. I haven't tried any 6L6 or any other beam power tube so I'm
open for any view. But from reading about others I got the impression that EL34 tubes
are doing well in triode mode.
Anyway to try to get back to topic I,ll just say that I'm looking forward to hear if maybe
others build it and tell us about their impressions. For myself I feel that I,m not ready to
deal with these high voltages. I still haven't finished my 'RLD' amp, but that's another story.
hear bad things about EL34:s so when a guy like nazaroo mentioned this, I just have to
ask. I find it intresting. I haven't tried any 6L6 or any other beam power tube so I'm
open for any view. But from reading about others I got the impression that EL34 tubes
are doing well in triode mode.
Anyway to try to get back to topic I,ll just say that I'm looking forward to hear if maybe
others build it and tell us about their impressions. For myself I feel that I,m not ready to
deal with these high voltages. I still haven't finished my 'RLD' amp, but that's another story.
The anti-triode works well and would indeed be something to try with any totem pole output stage.
http://www.diyaudio.com/forums/tube...sist-totem-pole-current-mirror-pp-hybrid.html
I wonder if Broskie reads this forum. It seems to be about a year lag between something coming up here and Broskie writing an article about it...
After the Aikido got a few bullet dings in it in that OTHER thread, we'll probably soon be seeing Mu followers (as output stages) ripped to shreads on TubeCad. He claims not to read the boards, must hear about new schemes from some subscriber email. Then maybe does a search on his new name for it and finds nothing. SRPP+, Impedance converters, Aikido input stage ... He does seem to find the original patents of some of these though, must read a lot at the P.O. Of course the P.O. suffers from the same thing being patented under 10 different names a lot too.
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May be I should publish my Nirvana topology before somebody start claiming rights on it. 😎
It is made of 2 pentodes with power JFET anti-triode load in output stage, local feedback from it to anode of the 1'st triode, and parafeed - like output through matching transformer. Global feedback to the 1'st cathode from secondary can be added if desired, either negative by voltage, or positive by current, or both.
It is made of 2 pentodes with power JFET anti-triode load in output stage, local feedback from it to anode of the 1'st triode, and parafeed - like output through matching transformer. Global feedback to the 1'st cathode from secondary can be added if desired, either negative by voltage, or positive by current, or both.
Well, I don't really care if nobody else does,
But it looks like 5 or 6 of you have conspired to hijack the thread to discuss tubes, two or three times.
It would have been more chivalrous and gentlemanly
if you had just started a thread on EL-34s or Output tubes.
Or just contributed your opinions to an already existing thread.
When people want to read about the Ju-Jutsu Amp,
I guess I'll have to try again and start with a clean thread.
Maybe I'll just post everything in the first post:
Then you can do whatever you like,
and people will be able to read about this topology
without having to wade through pages of your off-topic nonsense.
Or maybe SY or some other moderator could just chop the thread back
to my last post on the Ju-Jutsu topology.
It seems like a huge waste of your own time and effort,
but maybe thats what you guys need, to develop some posting sense.
But it looks like 5 or 6 of you have conspired to hijack the thread to discuss tubes, two or three times.
It would have been more chivalrous and gentlemanly
if you had just started a thread on EL-34s or Output tubes.
Or just contributed your opinions to an already existing thread.
When people want to read about the Ju-Jutsu Amp,
I guess I'll have to try again and start with a clean thread.
Maybe I'll just post everything in the first post:
Then you can do whatever you like,
and people will be able to read about this topology
without having to wade through pages of your off-topic nonsense.
Or maybe SY or some other moderator could just chop the thread back
to my last post on the Ju-Jutsu topology.
It seems like a huge waste of your own time and effort,
but maybe thats what you guys need, to develop some posting sense.
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