@Ale, I tried 1:7 line output transformer amorphous core but don't liked: could be I use grid leak resistor of 110K, can be the guilty of the poor SQ? Do you use the AVC between the zobel & the 330R grid resistor? It's necessary grid resistor for the 26 in this configuration?
TIA
Felipe
TIA
Felipe
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@Andy, sorry for a lot of OT, I open other thread about input step-up transformers
Cheers
Felipe
Cheers
Felipe
Thanks Felipe - I think another thread is better if you want to explore step-up transformers on the input. Of course, it's an issue with this thread as well, but you could go into more detail in another thread.
Meanwhile I think I've taken a nice step forward. I'm now listening to 10Y with a LL1660/18 used just as a plate choke with FT-2 coupling cap. This is just a provisional arrangement and I only have 14mA going through the 10Y. This is driving EL12n outputs into a LL1664 (3K). So nothing is optimised, but it's all working. I've just heard 8 tracks so far, Some Steely Dan, Herbie Hancock, Wagner and Janacek opera arias and some of Brahms Symphony 2.
Sound is nice, and I think this is quite a good result. Very promising. Very detailed and clean. And definitely a DHT type of sound. I'm a little wary of brightness with the EL12n, but here it's clean rather than bright. I'm just about comfortable with this. I really go for smoothness without any grain or edge, and the sound here stays just inside the ballpark. It needs a lot more listening and playing around with the plate choke, OPT and operating points, but I can tell that there's the makings of a good sound in there.
So here's one solution - drop the 300b and keep the DHT driver. I'm getting enough gain for my system with an output tube of around mu=20. No need for any step-up on the input. There are a few choices to explore here besides the EL12n, either in SE or PSE with a pair of tubes. I intend to go further with this solution - I rate it as very promising. Rod is probably sceptical of an output tube with a mu of 20, but it's been done in a few other amps, some with the EL12n. It's an interesting "wrong way around" concept, where the most gain is in the output tube. But here you get a real DHT sound.
So I can now pull out all my DHT drivers again. Next will be 26. Maybe 46 again. At some point I should try 4P1L and some others since 10Y and 46 aren't cheap options unlike the EL12n outputs. Early days but first impressions are that I'm feeling good about this solution - it works. It may even be the case that the best 300b amp isn't a 300b amp at all.
Meanwhile I think I've taken a nice step forward. I'm now listening to 10Y with a LL1660/18 used just as a plate choke with FT-2 coupling cap. This is just a provisional arrangement and I only have 14mA going through the 10Y. This is driving EL12n outputs into a LL1664 (3K). So nothing is optimised, but it's all working. I've just heard 8 tracks so far, Some Steely Dan, Herbie Hancock, Wagner and Janacek opera arias and some of Brahms Symphony 2.
Sound is nice, and I think this is quite a good result. Very promising. Very detailed and clean. And definitely a DHT type of sound. I'm a little wary of brightness with the EL12n, but here it's clean rather than bright. I'm just about comfortable with this. I really go for smoothness without any grain or edge, and the sound here stays just inside the ballpark. It needs a lot more listening and playing around with the plate choke, OPT and operating points, but I can tell that there's the makings of a good sound in there.
So here's one solution - drop the 300b and keep the DHT driver. I'm getting enough gain for my system with an output tube of around mu=20. No need for any step-up on the input. There are a few choices to explore here besides the EL12n, either in SE or PSE with a pair of tubes. I intend to go further with this solution - I rate it as very promising. Rod is probably sceptical of an output tube with a mu of 20, but it's been done in a few other amps, some with the EL12n. It's an interesting "wrong way around" concept, where the most gain is in the output tube. But here you get a real DHT sound.
So I can now pull out all my DHT drivers again. Next will be 26. Maybe 46 again. At some point I should try 4P1L and some others since 10Y and 46 aren't cheap options unlike the EL12n outputs. Early days but first impressions are that I'm feeling good about this solution - it works. It may even be the case that the best 300b amp isn't a 300b amp at all.
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Hi Andy, unfortunately it won’t fit. We’d need to create a new PCB for the LL1554, it takes time to design and figure out the jumper logic for flexible setup. If I get the gap at some point I’ll let you know.
Thanks
Ale
Interesting feedback Andy. Definitely by adding a DHT driver in your system will make a big impact in sound providing is well design and overall e2e system is optimal.
I will be building a simple RL12P35 (German pentode) with CFB and likely add a DHT driver, possibly the 801a.
I’m also WIP an 845/813 amp when the monster OPTs arrive. This will work really well with my new OB (Liionidas) speakers. I’m very happy with the change on the speakers and sounds amazing. The 300B can drive them in my small listening room, however they need a tad more power when you want to listen to at high levels
Cheers
Ale
I will be building a simple RL12P35 (German pentode) with CFB and likely add a DHT driver, possibly the 801a.
I’m also WIP an 845/813 amp when the monster OPTs arrive. This will work really well with my new OB (Liionidas) speakers. I’m very happy with the change on the speakers and sounds amazing. The 300B can drive them in my small listening room, however they need a tad more power when you want to listen to at high levels
Cheers
Ale
Hello Ale
Thanks for the information. A 300b amp is still on my radar with a good IDHT driver.
For now though, I've gone off in another direction with RSD EL12n outputs and a DHT driver, so no need for a step-up. Even in my very basic first 10Y version of this, which I'm sure I can improve on, I'm really enjoying the sound. So much in fact that I listened to the whole of Wagner's Die Meistersinger from beginning to end yesterday because I couldn't stop listening!
So my focus now has shifted to trying out DHT drivers again. Familiar territory for the last 15 years and I have modules ready to connect up. I'm a bit excited about this, even. Given a moderately high mu output stage, it works.
I see you have some new plans as well. Keep us in the loop!
Thanks for the information. A 300b amp is still on my radar with a good IDHT driver.
For now though, I've gone off in another direction with RSD EL12n outputs and a DHT driver, so no need for a step-up. Even in my very basic first 10Y version of this, which I'm sure I can improve on, I'm really enjoying the sound. So much in fact that I listened to the whole of Wagner's Die Meistersinger from beginning to end yesterday because I couldn't stop listening!
So my focus now has shifted to trying out DHT drivers again. Familiar territory for the last 15 years and I have modules ready to connect up. I'm a bit excited about this, even. Given a moderately high mu output stage, it works.
I see you have some new plans as well. Keep us in the loop!
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SV811-10, gives you a mu of 10 for the output, a DHT that was designed specifically for audio. There are NOS examples still out there on ePay etc. If you don't insist on max possible power output and are prepared for 800V of B+ you don't need A2, you can get decent output in A1.
I've heard it in A2 driven via IT with a high gm IDHT driver (6C45P) at 300B kinds of voltages and it sounded just fine.
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Keep in mind with DHTs that if you opt for higher mu, that will also tend to come with higher Rp.
I had all kinds of good tubes at one time, which I stupidly sold because I wasn't using them at the time. Like quite a few EL50, 4654, and indeed some SV811-10. I'm not keen on building with voltages much higher than 300v, something I avoid. But you're absolutely right to bring it up as an option. 211 likewise.
Speaking of 211, higher mu may well come with higher Ri though there are exceptions which make a medium mu output tube possible. I don't know the actual figure for the EL12n I'm using but it sounds fine at my higher current/lower a-k voltage operating point. I'm also going to try out some tubes in parallel, which will halve the Ri. It can all be done, and I think done well. Your point is well taken, though, and it could be an issue with tubes requiring higher primaries in the OPT.
Incidentally, while Rp is very usual for describing plate resistance, a few European data sheets differentiate between Ra = anode load, and Ri which is internal "plate resistance". It can be a bit unclear at times.
Speaking of 211, higher mu may well come with higher Ri though there are exceptions which make a medium mu output tube possible. I don't know the actual figure for the EL12n I'm using but it sounds fine at my higher current/lower a-k voltage operating point. I'm also going to try out some tubes in parallel, which will halve the Ri. It can all be done, and I think done well. Your point is well taken, though, and it could be an issue with tubes requiring higher primaries in the OPT.
Incidentally, while Rp is very usual for describing plate resistance, a few European data sheets differentiate between Ra = anode load, and Ri which is internal "plate resistance". It can be a bit unclear at times.
If the plate impedance isn't clear, look for mu and gm at a given operating point and calculate it, or head to the curves to double check!
I still say you should take the time to properly use a 4P1L as a pentode to drive a 300B.
I still say you should take the time to properly use a 4P1L as a pentode to drive a 300B.
No - I'm perfectly familiar with the theory. I was just saying that European data sheets distinguish between Ra (load) and Ri (internal) as you may have noticed. The American expression Rp is usually taken to be the European Ri.
I rigged up a 4P1L in pentode but never got it right, so I never got any good sounds out of it. I could go back to it as an option and try and get it to work.
I rigged up a 4P1L in pentode but never got it right, so I never got any good sounds out of it. I could go back to it as an option and try and get it to work.
There's also a DHT with a mu of 160 that would more than happily drive a 300B. 300B Miller capacitance will be a little bit of a problem, but not the end of the world. Grid current could be problematic though.
Here's the curves for a triode strapped EL12N. Let me know if you would have preferred a different tracer setup.
That's great - so useful!!
Is it possible to have a wider image with more grid voltages? Like each 2v or something?
Is it possible to have a wider image with more grid voltages? Like each 2v or something?
Here's the curves with 2V steps. Unfortunately I am not sure how to modify the image aspect ratio. I can't even get the eTracer window to go full screen. I'll try to figure it out as is has been bothering me anyways.
The report has gm, mu and Rp values on page 2. If you haven't seen it have a look. I believe that was a question somewhere earlier in the thread.
The report has gm, mu and Rp values on page 2. If you haven't seen it have a look. I believe that was a question somewhere earlier in the thread.
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Ah! That's nice, very nice indeed. Thank you!
It seems the Ri is just under 1K at the operating point. That explains why it's sounding nice into my 3K OPT. That's a much lower Ri than I was expecting.
It seems the Ri is just under 1K at the operating point. That explains why it's sounding nice into my 3K OPT. That's a much lower Ri than I was expecting.