Hi
I am trying to build an amp using an ECH83 valve/tube.
However, the curves in the datasheet mean little to me, since I can't plot a load line as normally I would do for a Pentode.
Anyone can explain this to me please?
Datasheet
http://www.r-type.org/pdfs/6ds8.pdf
Best regards
Pedro
I am trying to build an amp using an ECH83 valve/tube.
However, the curves in the datasheet mean little to me, since I can't plot a load line as normally I would do for a Pentode.
Anyone can explain this to me please?
Datasheet
http://www.r-type.org/pdfs/6ds8.pdf
Best regards
Pedro
Hola Pedrito.
You will be able to draw any loadline, but keep in mind the following two factors:
1.- Signal grid has remote cutoff characteristic so she will distort more than a common pentode (sharp cutoff) or triode of regular type;
2.- This kind of tubes with many elements usualy are much more microphonic compared to triodes or pentodes of normal use.
In any case, use the lowest G2+4 bias you can (usually 20~30V) and a load resistance between 100 and 500K. Not much more nor much less.
Good luck in any case.
You will be able to draw any loadline, but keep in mind the following two factors:
1.- Signal grid has remote cutoff characteristic so she will distort more than a common pentode (sharp cutoff) or triode of regular type;
2.- This kind of tubes with many elements usualy are much more microphonic compared to triodes or pentodes of normal use.
In any case, use the lowest G2+4 bias you can (usually 20~30V) and a load resistance between 100 and 500K. Not much more nor much less.
Good luck in any case.
Funny that I was thinking the other day what to do with a couple of heptodes that I got. Do you know if anybody has tried to use the extra grids for feedback?
I used EQ80 tubes in a differential pair injecting signal at G1 and NFB at G3 DC coupled from the output of the circuit. No precisely with ECH83.
You can try a compressor/expansor using the signal grid as DC volume control and oscillator grid as audio input. The triode may be used to amplify control signal and a 6AL5 as crest to crest (doubler) detector to control heptode gain. Already explained in the Langford-Smith's Radiotron Handbook.
You can try a compressor/expansor using the signal grid as DC volume control and oscillator grid as audio input. The triode may be used to amplify control signal and a 6AL5 as crest to crest (doubler) detector to control heptode gain. Already explained in the Langford-Smith's Radiotron Handbook.
@Osvaldo de Banfield
Can you, please, clarify the difference between remote and sharp cut-off?
Is remote like a soft cut-off while the Sharp is a hard cut-off?
Finally, which one is better for guitar amps?
Thanks
Pedro
Can you, please, clarify the difference between remote and sharp cut-off?
Is remote like a soft cut-off while the Sharp is a hard cut-off?
Finally, which one is better for guitar amps?
Thanks
Pedro
I'm not musician and I don't know their tastes and habbits, but if you like distortion, you can try injecting signal at G1. If you want little distortion, try G3. Gain is quite different for both.
For a discussion about remote or sharp cut off grids, please refer to proper literature. Sharp cutoff usualy closes quickly the electron stream to plate with increase in negative grid voltage. Remote cut off does it more slowly. In other words, you need a more heavy negative bias to cut the anode current than a sharp cut off.
For a discussion about remote or sharp cut off grids, please refer to proper literature. Sharp cutoff usualy closes quickly the electron stream to plate with increase in negative grid voltage. Remote cut off does it more slowly. In other words, you need a more heavy negative bias to cut the anode current than a sharp cut off.
Hi
Thanks. I knew this one and used it on my first attempt. What I don't really understand is why the cathode is grounded. We should have at least 1V on the cathode to have some clean headroom.
However the grid leak resistor is small, maybe that will generate a slightly negative voltage. And this would only affect the triode, whereas putting a resistor on the cathode will affect both triode and heptode.Maybe I am saying crap.... don't know. 😃
Cheers
Pedro
Thanks. I knew this one and used it on my first attempt. What I don't really understand is why the cathode is grounded. We should have at least 1V on the cathode to have some clean headroom.
However the grid leak resistor is small, maybe that will generate a slightly negative voltage. And this would only affect the triode, whereas putting a resistor on the cathode will affect both triode and heptode.Maybe I am saying crap.... don't know. 😃
Cheers
Pedro
There is always some negative potential at the grid, caused by electrons emmited from cathode striking grid wires and lateral rods. Also some bias is generated by contact potential. But for it to be effective, usually a large grid resistor is used, 4.7 to 22Megohms.
But in that project , as plate voltage is very low compared to usual values, rhere is no risk for the anode to run hot. My doubth in such example regards grid rectification that may cause severe distortion, but most musicians like distortion so I can't judge. Moreover, I never tried a tube in such conditions.
But in that project , as plate voltage is very low compared to usual values, rhere is no risk for the anode to run hot. My doubth in such example regards grid rectification that may cause severe distortion, but most musicians like distortion so I can't judge. Moreover, I never tried a tube in such conditions.
Valve car radios from the fifties used a power inverter with an electromagnetic vibrator to get high voltage. They did not use 12V for B+.
I didn't know that but makes sense. Usually Datasheets state a low maximum plate voltage (16V, 24V,...). Of course B+ can be much higher, which would give more headroom. And if I use 2 valves, I can use the pentodes in push-pull and that should be able to put some volume out.
Thanks for the info.
Cheers
Pedro
Thanks for the info.
Cheers
Pedro
What pentodes, dear? ECH83 is a hexode triode combined for Oscillator and Mixer in radio receivers.
Regarding maximum voltage it depends entirely on tube contruction: distance from electrodes, possibilty of arcing, glass electrolysis, etc.
Some time ago I read that the 50B5 a pentode for audio output in AC/DC radio receivers presented a fault. The anode pin was #5, and heater, #3 & 4. So under certain circumstances arcing between anode and heater took place destroying the tube, output transformer and socket. So Engineers move the plate to pin #6 and the screen to #5 reducing voltage gradient and called it 50C5. I certainly don't know if it was true, but seems feasible.
Regarding maximum voltage it depends entirely on tube contruction: distance from electrodes, possibilty of arcing, glass electrolysis, etc.
Some time ago I read that the 50B5 a pentode for audio output in AC/DC radio receivers presented a fault. The anode pin was #5, and heater, #3 & 4. So under certain circumstances arcing between anode and heater took place destroying the tube, output transformer and socket. So Engineers move the plate to pin #6 and the screen to #5 reducing voltage gradient and called it 50C5. I certainly don't know if it was true, but seems feasible.
Partial truth there. The 50B5 did not meet the new "creepage" rules imposed by UL. This led to the 50C5 which is exactly the same tube with the plat pin moved physically further away from the heater which was directly connected to the AC line. The whole circuit is a shock hazard to begin with, so this move made absolutely no sense.
Car radios from the 40's and early 50's did use a vibrator (mechanical switcher) based power supply to create about 300 volts from a 6 or 12 volt car battery. My first car was a 1949 Plymouth. Its radio used a pair of 6V6's in push pull from almost 300 volts. Yes, it was loud.
In the mid and late 50's "space charge" tubes were invented that did work with 12 volts on the plate. They really don't like 150 volts either! The radios from the late 50's and early 60's used tubes for all but the audio output stage, which used a big fat germanium transistor and an output transformer. Those were about the only useful parts I could get out of those old radios.
When Pete Millett came up with his Engineers Amplifier, I got a board and squeezed it for far beyond his 18 WPC. At power levels above about 50 WPC the 6CB6 couldn't make enough gain, so I started trying anything that would fit the socket. The higher Gm 6EW6 worked better, but the 6GU5 hexode was the gain and low distortion king. I just plugged it into the socket and tweaked the resistor values around it for a kick butt 125 WPC version. Details are scattered throughout the very long thread.
Car radios from the 40's and early 50's did use a vibrator (mechanical switcher) based power supply to create about 300 volts from a 6 or 12 volt car battery. My first car was a 1949 Plymouth. Its radio used a pair of 6V6's in push pull from almost 300 volts. Yes, it was loud.
In the mid and late 50's "space charge" tubes were invented that did work with 12 volts on the plate. They really don't like 150 volts either! The radios from the late 50's and early 60's used tubes for all but the audio output stage, which used a big fat germanium transistor and an output transformer. Those were about the only useful parts I could get out of those old radios.
When Pete Millett came up with his Engineers Amplifier, I got a board and squeezed it for far beyond his 18 WPC. At power levels above about 50 WPC the 6CB6 couldn't make enough gain, so I started trying anything that would fit the socket. The higher Gm 6EW6 worked better, but the 6GU5 hexode was the gain and low distortion king. I just plugged it into the socket and tweaked the resistor values around it for a kick butt 125 WPC version. Details are scattered throughout the very long thread.
VW has used 12V and even 6V on plates of small-signal tubes. Obviously with a transistor at the end to make audio power.
The "space charge" thing seems to be mostly audio drivers, 10-100 milliWatt. RF and IF tubes work at 12V. Not stunningly well, you may need one more stage to get the out-of-town ballgame on radio, but well-enough for many micro-Watts. Space-charge got you to many milli-Watts but probably with greater hiss and certainly some wacky curves.
Yes, my brother has the 1941 Plymouth radio. Being late Depression it is less than two 6V6 (maybe one 6F6??). He paid good money for a working vibrator but it had other problems.
R392/URR receiver was designed as a mobile version of R390A/URR. It used the same tubes , but with modified filaments, for 26 Volt. 6AK6, 6AK5, 12AX7 were not modified, but used the same 26V anode voltage. No surprise, at 26 volts B+ they worked as if at 260V.
In about 1955 a set of tubes was introduced into the European market: ECC86, ECH83, EBF83, EF97, EF98, which were dedicated to operate directly from a 12 V or even 6 V car battery. These tubes were invented by Philips, afaik, and they weren't space charge tubes.
To the original question: As the ECH83 was dedicated as the local oscillator and frequency changer in superheterodyne radios, it's no wonder that the datasheets only gives hints and curves for this application. You're lucky so far as the triode grid is being brought out on a dedicated pin, which isn't always the case with frequency changer triode-hexodes or triode-heptodes.
Best regards!
@Tubelab_com I love your comments about tubes and their history. You should write a book. Me buy the first printed.