for a source follower, the Crrs - Reverse Transfer Capacitance, is the thing to watch.....the lower the better.....
In a source follower the usual input capacitance (gate to source or Ciss) is bootstrapped since the source follows the gate. The output capacitance (drain to source or Coss) appears across the output which is driven by the low impedance output of the fet. The transfer capacitance (gate to drain or Crss) appears across the plate load of the driver tube so it is the dominant factor.
In chosing a source follower we want the Crss to be as low as possible and all of the capacitances to be constant across the voltage range seen by the fet in operation. The AO fet talked about earlier would be nearly ideal if operated above 100 volts (including signal swing). There are other fets with higher capacitances but go constant as low as 20 volts.
A capacitance that changes with applied voltage can cause PIM distortion, so we look to avoid VVC effects. VVC effects are associated with semiconductors, since their junction's depletion region changes in width with applied voltage. This is why we use mosfet followers (no junction) instead of BJT followers. Modern mosfets are now available with less capacitance than some tubes. VVC effects are also seen in vacuum tubes since the width of the space charge region is modulated by the control grid bias voltage, although this is a lossy capacitor with low Q, the effect can be measured.
I figured this out about 10 years ago. Many builders blindly make the same 6SN7 - 300B SE amps and they sound good with the usual simple female vocal music, but play some rock, jazz or techno, and YUKKKK. I use a high Gm triode (5842) loaded with a CCS and buffered with a mosfet follower to approximate an ideal triode and drive the grid out of a 300B if needed. My amp sings with the best of them, but ROCKS when it needs to. About 150 builders of them over the last 7 years seem to agree.
Thanks. Most of the family issues are resolved. I have some minor health issues, but do OK for a 60 year old. Work, well I still have a job.....have to bust my butt to keep it though.
My name is George, and I am a tubeaholic....Oh wrong meeting.....I have been torturing tubes since I was a kid and you could get all the tubes you wanted for free at the local trash dump inside all the discarded TV sets. My early fascination with these glowing things led to a career as an electrical engineer designing two way radios and cell phones......no tubes though.
In chosing a source follower we want the Crss to be as low as possible and all of the capacitances to be constant across the voltage range seen by the fet in operation. The AO fet talked about earlier would be nearly ideal if operated above 100 volts (including signal swing). There are other fets with higher capacitances but go constant as low as 20 volts.
A capacitance that changes with applied voltage can cause PIM distortion, so we look to avoid VVC effects. VVC effects are associated with semiconductors, since their junction's depletion region changes in width with applied voltage. This is why we use mosfet followers (no junction) instead of BJT followers. Modern mosfets are now available with less capacitance than some tubes. VVC effects are also seen in vacuum tubes since the width of the space charge region is modulated by the control grid bias voltage, although this is a lossy capacitor with low Q, the effect can be measured.
I figured this out about 10 years ago. Many builders blindly make the same 6SN7 - 300B SE amps and they sound good with the usual simple female vocal music, but play some rock, jazz or techno, and YUKKKK. I use a high Gm triode (5842) loaded with a CCS and buffered with a mosfet follower to approximate an ideal triode and drive the grid out of a 300B if needed. My amp sings with the best of them, but ROCKS when it needs to. About 150 builders of them over the last 7 years seem to agree.
Thanks. Most of the family issues are resolved. I have some minor health issues, but do OK for a 60 year old. Work, well I still have a job.....have to bust my butt to keep it though.
My name is George, and I am a tubeaholic....Oh wrong meeting.....I have been torturing tubes since I was a kid and you could get all the tubes you wanted for free at the local trash dump inside all the discarded TV sets. My early fascination with these glowing things led to a career as an electrical engineer designing two way radios and cell phones......no tubes though.
Still got those 4D32's you convinced me to buy. Cheaper than an EL156, and BIGGER! My soldering iron was hot for the first time this year last Thursday, so I'm slowy turning the corner. Still playing with little tubes for now. I'll get to the bigger ones a bit later. I got 26 more days to empty out my warehouse. Can't keep them all, got to figure out which ones to keep........All the big ones of course...except the 833A's......I have given up on that multi kilowatt guitar amp. I gave 6 of them to my boss, he wants to make a Tesla coil, and I sold the rest at Dayton.
"Thanks. Most of the family issues are resolved. I have some minor health issues, but do OK for a 60 year old. Work, well I still have a job.....have to bust my butt to keep it though.
My name is George, and I am a tubeaholic....Oh wrong meeting.....I have been torturing tubes since I was a kid and you could get all the tubes you wanted for free at the local trash dump inside all the discarded TV sets. My early fascination with these glowing things led to a career as an electrical engineer designing two way radios and cell phones......no tubes though. "
Glad to hear the situation is better. 62 and also started around 8 or 9. Got old radios, TV chassis and pulled tubes, resistors (and measured), leaky caps and any other parts we could pull. Remember Polypaks, Utah drivers etc. Those days were cool.
I'll think I will stay with the EL-156.
Cheers George and glad to meet you.
Steve
My name is George, and I am a tubeaholic....Oh wrong meeting.....I have been torturing tubes since I was a kid and you could get all the tubes you wanted for free at the local trash dump inside all the discarded TV sets. My early fascination with these glowing things led to a career as an electrical engineer designing two way radios and cell phones......no tubes though. "
Glad to hear the situation is better. 62 and also started around 8 or 9. Got old radios, TV chassis and pulled tubes, resistors (and measured), leaky caps and any other parts we could pull. Remember Polypaks, Utah drivers etc. Those days were cool.
I'll think I will stay with the EL-156.
Cheers George and glad to meet you.
Steve
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I worked as the service tech at an Olson Electronics store in 1971 and 1972. All the Olson brand guitar speakers were rebranded Utah's. Good speakers. That store was next door to the University of Miami. Lots of money flowed through that store, yet they still managed to screw it up. Polypaks was a cheap solid state source in the mid 60's. There is one old timer here that remembers "no time to test em".
Oh yes, PolyPaks was a place you ordered from and then tested each part after receiving the order. But it was a dozen for a buck or so.
Very early 60s as my brother ordered from Poly parts such as Ck722 transistors, germanium diodes etc. In 62-63 we finally ordered 2 Utah drivers and a Sony TC350 reel to reel (SS electronics) from Allied Electronics. Allied sent us two orders, so we called but they told us to keep both orders. Turned out one 350 had virtually no bass in both channels. I delved in and found the same electrolytic coupling capacitor in both channels was virtually open. Replaced and all was fine. Still have them.
Cheers.
Very early 60s as my brother ordered from Poly parts such as Ck722 transistors, germanium diodes etc. In 62-63 we finally ordered 2 Utah drivers and a Sony TC350 reel to reel (SS electronics) from Allied Electronics. Allied sent us two orders, so we called but they told us to keep both orders. Turned out one 350 had virtually no bass in both channels. I delved in and found the same electrolytic coupling capacitor in both channels was virtually open. Replaced and all was fine. Still have them.
Cheers.
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Hi,
An Tube such mentioned before is not a real EL156.
A real EL156..
..has a steel socket , the first digit in the european tube nomenclatur give information about the socket 1 = steel socket, 3 = octal socket 5 = magnoval and so on...
..withstands 800V plate voltage.Refer to the original Tfk data sheet:
http://www.mif.pg.gda.pl/homepages/frank/sheets/128/e/EL156.pdf
..are able to turn 45W plate power into heat.
And finally , these fine tube is one of the made-to-last high reliable output tube in the world. The original Tfk has a specified mtbf of abt. 10000 operating hours. I own some of them which have already a runtime of 15000hrs on the clock and all their parameters are still in specs. What a tube!!
73
Wolfgang
So the china fire cracker may be what else but not an EL156.
73
Wolfgang
An Tube such mentioned before is not a real EL156.
A real EL156..
..has a steel socket , the first digit in the european tube nomenclatur give information about the socket 1 = steel socket, 3 = octal socket 5 = magnoval and so on...
..withstands 800V plate voltage.Refer to the original Tfk data sheet:
http://www.mif.pg.gda.pl/homepages/frank/sheets/128/e/EL156.pdf
..are able to turn 45W plate power into heat.
And finally , these fine tube is one of the made-to-last high reliable output tube in the world. The original Tfk has a specified mtbf of abt. 10000 operating hours. I own some of them which have already a runtime of 15000hrs on the clock and all their parameters are still in specs. What a tube!!
73
Wolfgang
So the china fire cracker may be what else but not an EL156.
73
Wolfgang
So they put a socket on it that people actually use.
The aim is to sell them. Since the vast majority of pentode amps out there have international octal sockets, I consider that a smart move.
There are octal '2A3' valves out there too.
Drawback of the IO socket is the proximity of the anode pin to the heater pin. According to Mullard, the EL34 could handle 800V as well, but most sockets can not.
Long time ago (end of the '90s I guess) I compared my high power octal based valves in the amp I used at that time. Turn up the current until there is a faint red glow on the anode in a dark room. Worst were the Russian 6550's/KT88's: more than 25W and most of them would be red. The Chinese ones arrived till 28-30W. My vintage RCA (Tung-Sol) 6550's came close to 35W, but slightly red still. These are not anode dissipations, but anode + g2.
The Valve Art KT100 (octal-EL156) I could NOT get to glow. My amp didn't give me more than about 100mA each @ 480V (PP-UL). Not bad.
In this specific amp, I found the sound more triode like than my reference, the RCA/TS 6550.
I have 5 brand new NOS EL156 Real Telefunken in box , i bought them about 20 years ago, and waiting for me to do something with them. Didnt do an Amp yet because the high cost of the transformers, and i heard that this tubes can last for 50.000 hours or even more !!! maybe one of this days i put them for sale, i know i can get good money for the 5.
i'm not gonna tell you how to run them...
class a or ab both sound awesome with tubes
if your running small stuff a
if your running bigger stuff ab
tube wattige is different so i don't know why you need ab to run them thats a lot of power
anyway just wanted to say when you build it try droping the voltige on the power supply
not as much power but at a 100% all the time they will burn out quick
run them at 50 or a 100 volts below they'll last a lot longer
just remember a tubes and light bulbs are the same in that reaspect
class a or ab both sound awesome with tubes
if your running small stuff a
if your running bigger stuff ab
tube wattige is different so i don't know why you need ab to run them thats a lot of power
anyway just wanted to say when you build it try droping the voltige on the power supply
not as much power but at a 100% all the time they will burn out quick
run them at 50 or a 100 volts below they'll last a lot longer
just remember a tubes and light bulbs are the same in that reaspect
So you're saying the KT100 and the octal EL156 are the same tubes? Sorry, I can't follow you!
Best regards!
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