Very sorry if this has been done before but... Heres one for the experienced members of the forum.
Looking for an INDIRECTLY heated power tube, Serioulsly is the 6AS7G the only Triode? Linear as a dogs rear leg - looks good when lit up though.
I'm looking for any alternative to the triode trapped KT88 / EL34 but, for reasons of PSU reality am not willing (yet) to go DHT (no 300B / 845's then)
any pointers? even a "dont be daft" would be appreciated at this point....
Andy
Looking for an INDIRECTLY heated power tube, Serioulsly is the 6AS7G the only Triode? Linear as a dogs rear leg - looks good when lit up though.
I'm looking for any alternative to the triode trapped KT88 / EL34 but, for reasons of PSU reality am not willing (yet) to go DHT (no 300B / 845's then)
any pointers? even a "dont be daft" would be appreciated at this point....
Andy
This is a thread with several recommendations for double triodes.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=87501&highlight=
http://www.diyaudio.com/forums/showthread.php?s=&threadid=87501&highlight=
threads
Greetings Erik
Another thread! thanks (searching for power triode was perhaps , erm "optimistic")
but I read it and I'm none the wiser....
7236 looks good if I could find enough to warrant getting excited about. Same with the 6528 (like rocking horse dung) but a fantastic tube I'll grant you! "Sadly" Mr Jones made them rightly famous before I came along - maybe a re-issue? <anybody! maybe a Chinese or Russian manufacturer can help us out?> if you were gonna pick a tube it would be that one
What about the 6c33c? good? in P-P? or are there issues with stability? - I heard it tends to wander...
Ok at this point its perhaps worth pointing out that I tend to look for alternatives, for everything. But if there is an alternative to the triode strapped KT88's I'm considering I want to know about it!
On the other hand the lack of alternatives is perhaps why people put up with the 300b - dealing with the main's and signal at the same time? can't be fun... OK heres where the fun starts, perhaps
with a side order of 
Andy
Greetings Erik
Another thread! thanks (searching for power triode was perhaps , erm "optimistic")
but I read it and I'm none the wiser....
7236 looks good if I could find enough to warrant getting excited about. Same with the 6528 (like rocking horse dung) but a fantastic tube I'll grant you! "Sadly" Mr Jones made them rightly famous before I came along - maybe a re-issue? <anybody! maybe a Chinese or Russian manufacturer can help us out?> if you were gonna pick a tube it would be that one
What about the 6c33c? good? in P-P? or are there issues with stability? - I heard it tends to wander...
Ok at this point its perhaps worth pointing out that I tend to look for alternatives, for everything. But if there is an alternative to the triode strapped KT88's I'm considering I want to know about it!
On the other hand the lack of alternatives is perhaps why people put up with the 300b - dealing with the main's and signal at the same time? can't be fun... OK heres where the fun starts, perhaps
with a side order of Andy
SY is right. When triode wired, the 6V6 and its close relatives give nothing away in the linearity dept. to the highly revered 6SN7.
Because the suppressor grid is brought out externally, the EL34 offers options. Both g2 and g3 can be tied to the plate or g2 tied to the plate and g3 tied to the cathode. Sonic differences have been reported between the 2 arrangements.
woooah missed a load of posts. (slow typing)
El84's??? Really? these have been buggin' my subconcious for a while. The only point against them is that you need a lot for some OOmpH - Although *my* recent experiments imply that 5-10 watts is more than plenty - perhaps the subject of a diatribe in the future - depends how annoyed I get with a certain UK Hi-fi suppliers insistance you need 1000w for hi-fi...
6L6? now I had thought that this was similar to the EL34? please excuse my ignorance if not. But the EL34 sounds grand as a 'triode strapped pentode' (actually I think its great as a triode)
Eli, You can see, I completely agree about the EL34, specifically because its got every grid bought out its got plenty of play time. I just dumped KT88's in favour of them on a SE amp, it just worked better.
My question is. does anyone know of a better NOT DHT tube than triode strapped pentodes? At the moment the KT66 to my mind has the MOST beutiful curves (yeah, and maybe the Chinese copies are somewhere close)
I'm musing here I'll grant you. It seems incredible that the few manufacturers that are still making tubes give us 'n' variations of the 6550 but no uber triodes like the 6528.. or whatever
Andy
El84's??? Really? these have been buggin' my subconcious for a while. The only point against them is that you need a lot for some OOmpH - Although *my* recent experiments imply that 5-10 watts is more than plenty - perhaps the subject of a diatribe in the future - depends how annoyed I get with a certain UK Hi-fi suppliers insistance you need 1000w for hi-fi...
6L6? now I had thought that this was similar to the EL34? please excuse my ignorance if not. But the EL34 sounds grand as a 'triode strapped pentode' (actually I think its great as a triode)
Eli, You can see, I completely agree about the EL34, specifically because its got every grid bought out its got plenty of play time. I just dumped KT88's in favour of them on a SE amp, it just worked better.
My question is. does anyone know of a better NOT DHT tube than triode strapped pentodes? At the moment the KT66 to my mind has the MOST beutiful curves (yeah, and maybe the Chinese copies are somewhere close)
I'm musing here I'll grant you. It seems incredible that the few manufacturers that are still making tubes give us 'n' variations of the 6550 but no uber triodes like the 6528.. or whatever
Andy
Sy, I'm churning through the data now....
Acording to to the TDSL the 6L6 is a beam tetrode more akin to the KT** series. I'll grant you NOT the same as the EL' whatevers
(at which point my PC decided to take a rest fom acrobat and will need to be bounced) If so though, they suffer from the same ineffiency as the KT* series?
OK so I WAS looking for the data now... need to restart both my PC (and me)
Dont get me wrong I LIKE the way the KT88 works. As a triode it should be pretty 'triodey' (?)
Meanwhile "AB2?" - to my shame I've given up on that. There are big numbers to be had there, but driving grid current is too much like hard work
cake and eating it, what at the SAME TIME?
Andy
Acording to to the TDSL the 6L6 is a beam tetrode more akin to the KT** series. I'll grant you NOT the same as the EL' whatevers
(at which point my PC decided to take a rest fom acrobat and will need to be bounced) If so though, they suffer from the same ineffiency as the KT* series?
OK so I WAS looking for the data now... need to restart both my PC (and me)
Dont get me wrong I LIKE the way the KT88 works. As a triode it should be pretty 'triodey' (?)
Meanwhile "AB2?" - to my shame I've given up on that. There are big numbers to be had there, but driving grid current is too much like hard work
cake and eating it, what at the SAME TIME?
Andy
Depending on how much power you need you might also want to consider the 6CK4.. Very inexpensive, very linear, about 10 - 12W in PP, and maybe 2W in SE. I've used them SE, PP and as drivers for 2A3, good ones sound a lot like the 45, are easier to drive due to their significantly higher mu..
Andy,
Power MOSFETs are your friends when grid current is in the picture. DIY member Tubelab has his power drive board. A favorite link of mine is MOSFET Follies. The IRFBC20 is (IMO) a part to consider. Take a look at the IRFBC20 data sheet. The low and stable reverse transfer capacitance is particularly interesting.
Ahhh I found an easy way to do this... Duncan Amps TDSL personal edition allows you to "search by type"
Initially I looked for tubes with more than 10w dissipation, but quickly decided on 20 watts for practicality, As it turns out there are quite a few options IF you could find the tubes 
Anyway...
To evaluate the different types of tubes I set about drawing an arbitrary loadline (4 x Ri) measuring the standard deviation between the curves on that loadline. (Operating point as described in the datasheet where possible)
Best 'so far' are the triode strapped EL34, 6v6, and the KT88
Without starting a bun fight. I was using as my reference the 300B, but I've come unstuck a bit there. The operating point used was Va=300v/60Ma/-61v If thats reasonable then it leads me to think that in this respect its only a little better than a triode strapped EL34
In fact the better ones are all around 3 - 4 devations (the 6AS7 comes in at 21 and I had to fudge the figures to get that...)
So I'm sticking with the EL34 or the KT* types for the time being, at least the iron is easy to get hold of. Or at least better iron ought to be.
Andy
Initially I looked for tubes with more than 10w dissipation, but quickly decided on 20 watts for practicality, As it turns out there are quite a few options IF you could find the tubes
Anyway...
To evaluate the different types of tubes I set about drawing an arbitrary loadline (4 x Ri) measuring the standard deviation between the curves on that loadline. (Operating point as described in the datasheet where possible)
Best 'so far' are the triode strapped EL34, 6v6, and the KT88
Without starting a bun fight. I was using as my reference the 300B, but I've come unstuck a bit there. The operating point used was Va=300v/60Ma/-61v If thats reasonable then it leads me to think that in this respect its only a little better than a triode strapped EL34
In fact the better ones are all around 3 - 4 devations (the 6AS7 comes in at 21 and I had to fudge the figures to get that...)
So I'm sticking with the EL34 or the KT* types for the time being, at least the iron is easy to get hold of. Or at least better iron ought to be.
Andy
Eli Duttman said:
Until recently I hadnt completely ruled out Mosfets as the output stage... they aren't so pretty though. (A great technical reason if ever there wasn't one)
Thanks for the link though I'm trying to get a list of "tube compatible" transistors. I'm quite keen on the use of solid state if it helps.
Andy
What Eli meant was using them as source followers to drive the output stage. There are a lot of good candidates to do that- the high-performance king for me so far is a DN2540 cascode source follower. The measly few dozen milliamps that my output tubes' grids need doesn't even make them break a sweat.
SY said:
Sy, would you kindly post a schematic.
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Andy, we use cascoded DN2540s as current sinks in "El Cheapo". The idea originates with Bandersnatch.
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