off hand, i don't know what the right point is! calculate it yerself! 450 on the plate could be around -20 volts or so. educated guess. i'd guess the cathode can do 100mA at lower voltages... test it with chinese tubes, before you plug in the good stuff. but, the input impedance would swing around quite a bit. negative grid current at quiescent, and then a fast null and swing positive very quickly. clipping climbs through the roof. A2 works great with 211s. at low plate voltage, i'd keep that in mind. in any case, the lower the driver stage impedance, the better.
for me, though, transmitting tubes are a pain the ***. the heater current is just a drag. given the trouble of dealing with em in the first place, why not just make a 1300 volt supply? at least, then, it's worth the trouble. 30 watts. if you have kids and animals, why bother with them at all. make a russian or chinese 300B amp. or, even more interesting, a television sweep tube or vertical amplifier tube. cheap, plentiful and different... and excellent. parallel a bunch of them and make a beast of an amp. makes the speaker choices easier.
as for the "sound" of tubes, it all depends on what you do with them. they can be made to sound very differently. they do have a basic character of their own, but that never matters independently of all the other parts. 211's are on their own, a bit bright and brassy... but, use a high Z driver and cap couple and they are dull and slow. the ongaku is an example of a amp with a good balance of impact and smear... makes bright compressed pop listen-able and yet pulls color out of software that doesn't really have much to begin with.
i don't think there is much i can do to help guide you with the subtle taste stuff. it's personal and takes time to develop. but the big stuff, the basic house cleaning of good design is still the most important. start by doing it by the book!
jc
for me, though, transmitting tubes are a pain the ***. the heater current is just a drag. given the trouble of dealing with em in the first place, why not just make a 1300 volt supply? at least, then, it's worth the trouble. 30 watts. if you have kids and animals, why bother with them at all. make a russian or chinese 300B amp. or, even more interesting, a television sweep tube or vertical amplifier tube. cheap, plentiful and different... and excellent. parallel a bunch of them and make a beast of an amp. makes the speaker choices easier.
as for the "sound" of tubes, it all depends on what you do with them. they can be made to sound very differently. they do have a basic character of their own, but that never matters independently of all the other parts. 211's are on their own, a bit bright and brassy... but, use a high Z driver and cap couple and they are dull and slow. the ongaku is an example of a amp with a good balance of impact and smear... makes bright compressed pop listen-able and yet pulls color out of software that doesn't really have much to begin with.
i don't think there is much i can do to help guide you with the subtle taste stuff. it's personal and takes time to develop. but the big stuff, the basic house cleaning of good design is still the most important. start by doing it by the book!
jc
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I have never seen the other schematics I'll keep an eye out..
I know what you mean about the heater current on some of the exotic tubes..you need a power station just to warm them up...6C33c comes to mind..LOL
There has been quite a few projects with sweep tubes here..I hope you have as much fun here as we do...some interesting photos in the gallery..
I had a look at your blog some interesting designs..
Great to meet you here!
M. Gregg
Thats interesting a 300B Dinosaur...now there is a thought..
Wonder what it would sound like..
Thanks. Its interesting that the FET has gone wonder why?
Regards
M. Gregg
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the fet is gone because i don't have the cathode follower anymore. i have the 2 sections of medium mu tube... it's more than enough gain. the direct coupled driver/output stage accomplishes the requirements without the cathode follower... getting rid of the cap got rid of the problems. of course the power supply becomes more complicated. but the performance improved. i liked the fet version a lot! and the next step was to get rid of all the caps. but in this case, i needed the 3000p because it was the hi pass crossover for my bi-amp.
Would there still be enough drive for the 845?
I guess the 3000pF could be 0.1 for normal use?
Regards
M. Gregg
an 845 is an "easier" load to drive than a 211. the low mu/wide grid spacing makes the grid current changes more gradual and less of an issue. i would be hard pressed to use a 100k grid resistor on a 211, but have no problem using a bit more for an 845. we are talking about self biased stages here and RC coupling. 10k max for a 211... it just varies too much for cap coupling. direct coupling the grid to the driver eliminates the problem up to the diode line. of course, a cathode follower can be designed with a very low output Z, and one could drive the grid positive without difficulty. a great system for this is driving the cathode and grounding the grid. A2 operation of a grounded grid output stage would be the way to do a low B+ arrangement for a 211... you could also use a lower impedance output trans as well, making it all a bit safer and cheaper for a first time transmitting tube project...
I must admit I have never seen cathode drive used?
Do you have a link to an example?
Regards
M. Gregg
Is this what you mean?
Its a PDF...
http://www.google.co.uk/url?sa=t&rct=j&q=cathode%20drive%20circuit%20triode&source=web&cd=2&sqi=2&ved=0CCQQFjAB&url=http%3A%2F%2Fn4trb.com%2FAmateurRadio%2FRCA_Ham_Tips%2Fissues%2Frcahamtips1903.pdf&ei=GjoPT86eDYOL8gPv29WBBA&usg=AFQjCNGVQksPe4C5BA2IhpNkW4oxJHAfCQ
I will have to look further to see how this could be used to drive an output tube....
Regards
M. Gregg
Its a PDF...
http://www.google.co.uk/url?sa=t&rct=j&q=cathode%20drive%20circuit%20triode&source=web&cd=2&sqi=2&ved=0CCQQFjAB&url=http%3A%2F%2Fn4trb.com%2FAmateurRadio%2FRCA_Ham_Tips%2Fissues%2Frcahamtips1903.pdf&ei=GjoPT86eDYOL8gPv29WBBA&usg=AFQjCNGVQksPe4C5BA2IhpNkW4oxJHAfCQ
I will have to look further to see how this could be used to drive an output tube....
Regards
M. Gregg
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JC,
Are you talking about using a Tx in the cathode / secondary as (load) primary input or cap coupled...I guess DC coupled would set the bias?
I am aware of the cathode being an input but...New area for me...I guess others have used this? shout up if you have...
Is this just a case of Dc coupling the cathode to set the bias and ground the grid with 1 Ohm resistor or am I on the wrong track?
Regards
M. Gregg
Are you talking about using a Tx in the cathode / secondary as (load) primary input or cap coupled...I guess DC coupled would set the bias?
I am aware of the cathode being an input but...New area for me...I guess others have used this? shout up if you have...
Is this just a case of Dc coupling the cathode to set the bias and ground the grid with 1 Ohm resistor or am I on the wrong track?
Regards
M. Gregg
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To post an image click "Post Reply" go down to manage attachments this will open a browser window...... browse to the image on your PC location if its the correct size click upload and your done..If you want an image in windows seven there is a standard program called "snip it" cuts a piece out of the screen..You can resize an image in windows 7 also..click the picture then edit organize then click the picture to open it then in the drop down tab called properties click resize..and save you should then have a smaller size pic next to the original..in the file on your PC..
To locate "snip it" in the program search bar type "snip" it will give you the start icon..
Regards
M. Gregg
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Well I have been reading the blog..
After a bear a dog or sheep then rainbows...ummm
Looked closley and saw what seems or could be a cathode auto bias with something that reminds me of the mozener on the otl...a FET strapped across the cathode circuit that is being driven by the driver stage...can't make out if the grid has some kind of fixed bias...Then again if the diagrams in info I posted have any relevance a cap coupled to the cathode would create drive..I will look at the blog when you have posted..Thank's
Might be worth trying to upload here just for fun...
Regards
M. Gregg
After a bear a dog or sheep then rainbows...ummm
Looked closley and saw what seems or could be a cathode auto bias with something that reminds me of the mozener on the otl...a FET strapped across the cathode circuit that is being driven by the driver stage...can't make out if the grid has some kind of fixed bias...Then again if the diagrams in info I posted have any relevance a cap coupled to the cathode would create drive..I will look at the blog when you have posted..Thank's
Might be worth trying to upload here just for fun...
Regards
M. Gregg
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