Read the early tube manuals such as RC12 and look at the design examples in the back. For example the 6C6 / 57 is shown triode strapped as a mic preamp (design 17 p. 149 as well as the input stage to amplifiers)
In addition some of the early datasheets provide triode strapped curves although most of these are for power Pentodes .
In addition some of the early datasheets provide triode strapped curves although most of these are for power Pentodes .
Here is an imaginative use of pentodes . He doesn't say how he got on . Having built similar I think it will work very well . What might surprise people is the so called pentode distortion is a bit of a myth. One gets it if one wants it . By cunning design it isn't a given . Some will say is it any different to a triode if equaling a triode ? Sometimes there is a free lunch in terms of gain .
Tube DIY Asylum
Tube DIY Asylum
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It depends on the tube- certainly, a remote cutoff pentode will be a lousy choice, even with the extra feedback. But a good sharp-cutoff pentode will start with reasonable linearity, and the extra gain will take it the rest of the way home. As a bonus, you'll drop the output impedance of the amp more with the higher feedback (i.e., better damping).
I didn't want to leave my statement hanging in the air . Here are the graphs of my similar amp . I made it for a friend who perhaps would like to keep the circuit to himself .
All pentode with UL feedback to output . No loop feedback . The intention was to meet the old DIN 45500 standard . For much of the time it had a transistor current source and sink . In the end even they went . Distortion at 1 watt is 1 % all second harmonic and so it goes right down to mW . With a transistor current source distortion was 0.1% at 1 watt . The THD is perhaps 1.5 % at 8 watts . I didn't bother to calculate it . 8.4 watts at clipping . The 8 watts spectrum is not bad seeing how close it is to clipping . It sounds like a very good triode ( 300 B ) . In fact the friend was testing 300B's when he first listened to it . I feel we were closer to the expensive ones ( WE ) . These valves are more often used in guitar amps . The 1% is if you like the line I didn't want to cross , these are my notes so forgive .
All pentode with UL feedback to output . No loop feedback . The intention was to meet the old DIN 45500 standard . For much of the time it had a transistor current source and sink . In the end even they went . Distortion at 1 watt is 1 % all second harmonic and so it goes right down to mW . With a transistor current source distortion was 0.1% at 1 watt . The THD is perhaps 1.5 % at 8 watts . I didn't bother to calculate it . 8.4 watts at clipping . The 8 watts spectrum is not bad seeing how close it is to clipping . It sounds like a very good triode ( 300 B ) . In fact the friend was testing 300B's when he first listened to it . I feel we were closer to the expensive ones ( WE ) . These valves are more often used in guitar amps . The 1% is if you like the line I didn't want to cross , these are my notes so forgive .
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This standard assumes that the output power is 10 W minimum with max. 0,5 % THD and IMD. With any 5 W amplifier this standard can not be fulfilled.
Intention . Here is the 12 watts , 10 would be a bit nicer than 12 . Same everything except g2 settings this version and my preferred 5 watt version as you call it . Please forgive my shorthand for UL taps . The amplifier is a genuine 8 watts . It has 5 excellent watts .
Look at the 8 watts from the amp that more easily gives 8 watts ( 8 of 12 ) . Not my cup of tea . 8 of 8.4 is not bad .
I did get a DIN45500 version to work . It had loop feedback ( 9.5 db ) . I forget what file name it had ( there are 10's maybe 50+ files of this amp ) . The friend wouldn't have wanted a loop feedback amp nor transistor CCS . The transistor CCS was remarkable . I used 3 x 1N4148 as that seems to be better when setting reference voltage than anything else tried . Unlike most valve people I used a MJE 350 . It was excellent . Also LM 317 replaced by BD139 as a sink . It took days to better the LM317 . The one thing the transistors gave was a clue as to what should be possible . None of the graphs shown are with transistors .
One thing I did try was a signal activated bias idea . Worked a treat and got some excellent power . No obvious problems . Again my friend wouldn't have wanted it .
I hope everyone can see how pentode can be made to work . The all triode version was about 4 % THD and very insensitive ( similar spectrum ) . It had no wow factor to say it as worth the trade off over pentode . My PP amp is all triode .
Look at the 8 watts from the amp that more easily gives 8 watts ( 8 of 12 ) . Not my cup of tea . 8 of 8.4 is not bad .
I did get a DIN45500 version to work . It had loop feedback ( 9.5 db ) . I forget what file name it had ( there are 10's maybe 50+ files of this amp ) . The friend wouldn't have wanted a loop feedback amp nor transistor CCS . The transistor CCS was remarkable . I used 3 x 1N4148 as that seems to be better when setting reference voltage than anything else tried . Unlike most valve people I used a MJE 350 . It was excellent . Also LM 317 replaced by BD139 as a sink . It took days to better the LM317 . The one thing the transistors gave was a clue as to what should be possible . None of the graphs shown are with transistors .
One thing I did try was a signal activated bias idea . Worked a treat and got some excellent power . No obvious problems . Again my friend wouldn't have wanted it .
I hope everyone can see how pentode can be made to work . The all triode version was about 4 % THD and very insensitive ( similar spectrum ) . It had no wow factor to say it as worth the trade off over pentode . My PP amp is all triode .
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while i do not have the 6M11, i do have the 6BH11 and is using them intwo current power amp builds...also cheap at a dollar a pop at Rogalskie's...
this tube makes implementation of the mullard 5-20 topology a single tube thing...
This is called Schade feedback and was described in a different implementation but exactluy the same principle by the inventor of the Beam tetrode (BPT), specifically the 6L6 and derivatives. There was a thread discussing it at length about a year ago.
This is usable for all sorts of 'pentode curve' amplification devices, includin silicon - and, to a lesser extent to triodes. Essentially it implements externally what triodes implement by design, but with a different trade-off: the input capacitance stays pentode-like (very low) but input impedance drops drastically. The bonus part is that the external local feedback is variable through the choice of the plate voltage divider ratio, so you can essentially build a whole family of triodes out of a single type pentode or BPT (or MOSFET, or JFET, or BJT...)
Either import from USA or direct from China. there is no demand for Compactrons in Europe.
I recently got some Chinese Masgnoval sockets from Germany though.
Shoog
I tried the so called plate to plate feedback on my amp and quickly discovered it to be less effective than suggested . In fact my interest in pentodes came from critics of Alex Kitic ( RH 88 ) who suggested the ECC 81 was pointing the way to a pentode . Here below is the ultimate Kitic type amp using FET input ( Michael Koster ? ) . The FET much like a pentode . This amp produces about 2% THD I think and 5 watts . Distortion in suspension bridge decay . I haven't looked carefully at the FET version and I may have details wrong , if so forgive . The critics maintain that an even higher anode resistance is required if V1 is to become a proper V to I converter . The ECC81 is good , also ECC82 in cascode ( V2 cathode about 95V ) . A pentode is better . EF184 is ideal as it becomes almost an ECC81 if a triode . Thus one can start where Kitic left off . He was very certain he got it right . I say no as the distortion levels are very high and sensitivity nothing special . Kitic says I think 14 W and 1% distortion for this example . I never got that .
The inventor of the Beam Tetrode was Harries ( spelling ) Valve Company London 1935 and improved by EMI with the beam plates ( to avoid pentode patent it is said ) . Sold to Mr Schade and RCA by EMI MOV . By 1938 I think Fender were using 6L6 with Schade type circuit ? If my memory is right 807 was the valve Shade designed it for as it has some quirks ( more distortion compared with 6L6 ) . KT 66 is a repatriation of 6L6 . LS 50 the most exciting version ( Gu /Fu 50 ) . I think the name Schade was coined as a generic for this type of idea . I have lost a diagram of a RCA circuit idea much like a Dynaco using 7199 with Schade ( circa 1960 ) . Looking at it I suspect the idea of the Dynaco came from the marketing of the TV style 7199 valve to the audio designers . A pentode section with high gain and a DC coupled concertina splitter triode . If Dynaco saw the idea it didn't inspire Mr Hafler to use it .
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If you are prepared to do some reading this is interesting . Often the originator is far more informative than those who follow , not least here . P 360 about shunt feedback especially . He names Shepard . Much to my surprise this all looks new to them ! I had assumed Harold Black had covered it ?
Mostly people think of g2 strapped to anode as a triode . It is very nearly a triode . I think shunt feedback also qualifies . Not sure I came to a conclusion as to which of the fake triodes is best ? I think Kitic may have a point that one can get a little more out of a pentode ( beam tetrode ) than just strapping it's g2 to anode . He suggests that Rp is lower in his circuit than fake triode ( he seems to ) . I wonder , it might just be true . That V to I , I to V arrangement might be more cunning than it looks .
http://www.clarisonus.com/Archives/TubeTheory/Schade 1938 Beam Power Tubes.pdf
Mostly people think of g2 strapped to anode as a triode . It is very nearly a triode . I think shunt feedback also qualifies . Not sure I came to a conclusion as to which of the fake triodes is best ? I think Kitic may have a point that one can get a little more out of a pentode ( beam tetrode ) than just strapping it's g2 to anode . He suggests that Rp is lower in his circuit than fake triode ( he seems to ) . I wonder , it might just be true . That V to I , I to V arrangement might be more cunning than it looks .
http://www.clarisonus.com/Archives/TubeTheory/Schade 1938 Beam Power Tubes.pdf
It is kinkless tetrode, i.e. dynatron effect had been minimized by geometry. They also were called "Critical Distance Tetrode". Instead of 3'Rd grid like in pentodes, or beam plates like in beam - tetrodes, due to spacing the electron beam itself worked as a suppressor.
Actually, totally different beast: pentode that has nothing in common with 6L6.
That's the point . They are all pentodes of a different type . Philips had the patent . I think LS 50 was called a Ray Pentode by some ?
Someone said EL 34 was a fight back . My ears prefer it to many beam devices . Gu 50 the best of breed ?
GU-50 - Wikipedia, the free encyclopedia
Someone said EL 34 was a fight back . My ears prefer it to many beam devices . Gu 50 the best of breed ?
GU-50 - Wikipedia, the free encyclopedia
Fight was between 807 and LS-50 when they were used in transmitters of Allies against German transmitters? May be. Allies changed cheaper tubes more often, no big deal. They were made at least in US, GB, USSR. LS-50 were made by Telefunken only.
EL34 I believe was designed for audio amplifiers especially. And it is a good tube. If not overpriced, I would use it since it has more convenient base, socket, looks better than GU-50, even though it has cheaper design and manufacturing.
EL34 I believe was designed for audio amplifiers especially. And it is a good tube. If not overpriced, I would use it since it has more convenient base, socket, looks better than GU-50, even though it has cheaper design and manufacturing.
I've heard the old story that RCA acquired the rights to the beam tetrode to avoid paying royalties to Philips for the pentode. But RCA made any number of small signal pentodes, so didn't they have to pay the rights after all? Why didn't they come up with teeny little small-signal beam tetrodes?
807 and LS50 true .
As I understand it EL 34 was a product of hurt pride . The other people had stolen the publicity war . EL 34 was to be almost as good for less money . It is my favorite by a long way . As far as I know all beam tetrodes are kink-less . KT is just a name . Perhaps MO had already registered the name before selling to RCA ? New stock EL34 are as little as $20 a piece even in the UK . I have some old ones marked Marshall that are very good . I wonder if they are Mullard ? I used to sell new production MO KT 66 and 88 in 1974 . I bought them from Lugtons I think ? At $12 a piece ( 88's ) I was embarrassed to say how much when people bought them . The book my friend had was new for 1972 promoting designs using KT88 .
Having read Mr Schade's paper he certainly understood the device . The curves to my eyes look like pentodes .
The TT21 is a nice device . The story I heard is some young technicians had some KT 88 modified to resemble 807 . It fitted maximum allowed transmitter power for certain licenses . They offered the production ladies some dance tickets to say thank you . They showed them to their boss on Monday morning who instantly put them into production .
I think even to this day beam tetrodes seem to suggest superiority . One has to argue the case for pentodes strongly as it always seems to be implied that it is the poor relation .
Beam Power Tetrode
As I understand it EL 34 was a product of hurt pride . The other people had stolen the publicity war . EL 34 was to be almost as good for less money . It is my favorite by a long way . As far as I know all beam tetrodes are kink-less . KT is just a name . Perhaps MO had already registered the name before selling to RCA ? New stock EL34 are as little as $20 a piece even in the UK . I have some old ones marked Marshall that are very good . I wonder if they are Mullard ? I used to sell new production MO KT 66 and 88 in 1974 . I bought them from Lugtons I think ? At $12 a piece ( 88's ) I was embarrassed to say how much when people bought them . The book my friend had was new for 1972 promoting designs using KT88 .
Having read Mr Schade's paper he certainly understood the device . The curves to my eyes look like pentodes .
The TT21 is a nice device . The story I heard is some young technicians had some KT 88 modified to resemble 807 . It fitted maximum allowed transmitter power for certain licenses . They offered the production ladies some dance tickets to say thank you . They showed them to their boss on Monday morning who instantly put them into production .
I think even to this day beam tetrodes seem to suggest superiority . One has to argue the case for pentodes strongly as it always seems to be implied that it is the poor relation .
Beam Power Tetrode
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