Hi
I hope you are all well.
There are quite a few DHT preamps/schematics, and many of them use Gyrator anode load for DHT, like the one i have attached.
I was wondering if vacuum tube-like another triode/pentode could be used in place of gyrator to build some kind of MU stage for DHT tube?,
I haven't come across such a thing anywhere, perhaps not possible or make no sense, please let me know if any of you have ever built such a thing?
best.
Kr.
I hope you are all well.
There are quite a few DHT preamps/schematics, and many of them use Gyrator anode load for DHT, like the one i have attached.
I was wondering if vacuum tube-like another triode/pentode could be used in place of gyrator to build some kind of MU stage for DHT tube?,
I haven't come across such a thing anywhere, perhaps not possible or make no sense, please let me know if any of you have ever built such a thing?
best.
Kr.
Member
Joined 2009
Paid Member
thank you.
I'm looking but not seeing anything that I'm after, the Tram 2 looks more like it.
looking at the Tram2 schematics,
there is 6as7 triode used on top of DHT anode and CCS as well, I'm wondering if anyone can help with that CCS circuit as it's not described well in the TRAM2 pdf, or is there a way to get rid of that CCS (FET) and built just pure tube active anode load?
please let me know if you have any or can provide any schematics of it.
thank you.
Kr.
there is 6as7 triode used on top of DHT anode and CCS as well, I'm wondering if anyone can help with that CCS circuit as it's not described well in the TRAM2 pdf, or is there a way to get rid of that CCS (FET) and built just pure tube active anode load?
please let me know if you have any or can provide any schematics of it.
thank you.
Kr.
Attachments
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The CCS looks like it makes a constant-current cathode bias for the 6AS7, which acts as the current source for the 45. It's kind of hard to say exactly what's going on because there's no schematic for the "DIY HFS CCS PCB".
I know and that's a shame, unless someone here has or had Tram2 preamp and can provide schematics for the pcb?, that would be fantastic.
Why not DIY a 45 preamp with a mu follower?
Does this project have to be the best line preamp with gain ever made? Or would 'really good' be good enough?
The power supply would likely be at least as important to the sound as the audio circuit. Maida Done Right regulator? Morgan Jones Statistical Regulator? Salas shunt reg? Other?
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PS - I don't see the advantage of having a low-mu pass tube like 6AS7 in the CCS. Perhaps the DIY HFS CCS was not able to deliver the current needed for the 45 so the 6AS7 takes the heat? A DN2540 MOSFET can deliver the necessary current by itself, given an adequate heat sink.
Does this project have to be the best line preamp with gain ever made? Or would 'really good' be good enough?
The power supply would likely be at least as important to the sound as the audio circuit. Maida Done Right regulator? Morgan Jones Statistical Regulator? Salas shunt reg? Other?
--
PS - I don't see the advantage of having a low-mu pass tube like 6AS7 in the CCS. Perhaps the DIY HFS CCS was not able to deliver the current needed for the 45 so the 6AS7 takes the heat? A DN2540 MOSFET can deliver the necessary current by itself, given an adequate heat sink.
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45 preamp with MU follower sound like a way to go as well...really good is good enough.
...can you provide any schematics or it?
thank you.
The diyhifisupply CCS manual suggests it is a IXP10M45S, the manual also has the circuit diagram
I read an article years ago from Thorsten L saying the design of the Tram 2 was inspired by a design he saw which used a choke instead of the CCS. I did track it down at the time but I cant find either now unfortunately
Lost track of the original question...
Yes, you can make a textbook mu follower with a twin-triode and use that for a line stage, one twin-triode per channel.
However, the whole point behind a mu follower is that it maximizes the gain from the tube, and you don't need much gain at all in a line stage (2X to 3X is usually plenty).
A 6SN7 would be a good candidate, but would require something like a +400V DC plate supply, and its mu is approximately 20. That would result in a line stage with about 18X gain, or 25dB.
6N6P or ECC99 work with lower plate voltages, so could be used with something like a +300V DC supply. 6N6P has a mu of 16, so expect gain of about 14X. That's 23dB gain. Again, that's over the top.
So, as always, the first question is 'how much gain do you need?'
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Yes, you can make a textbook mu follower with a twin-triode and use that for a line stage, one twin-triode per channel.
However, the whole point behind a mu follower is that it maximizes the gain from the tube, and you don't need much gain at all in a line stage (2X to 3X is usually plenty).
A 6SN7 would be a good candidate, but would require something like a +400V DC plate supply, and its mu is approximately 20. That would result in a line stage with about 18X gain, or 25dB.
6N6P or ECC99 work with lower plate voltages, so could be used with something like a +300V DC supply. 6N6P has a mu of 16, so expect gain of about 14X. That's 23dB gain. Again, that's over the top.
So, as always, the first question is 'how much gain do you need?'
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45 with a triode as the plate load for mu follower configuration? That can certainly be done. Explanation of mu follower:
The Valve Wizard -Mu Follower
The problem with using a 45 as a line stage is hum from the filament. That's because the 45's cathode and heater are one and the same (the 'filament'). Will you be using something like a Rod Coleman filament regulator? Filamentary bias?
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yes, you are right, x14 gain is over the top but I can try it for a dac output instead, or give it a go as a preamp.
sounds very interesting with ecc99 as mu and 45 under, I have those tubes on hand in fact and 300v anode voltage is great too.
would be kind enough to provide any schematics of it?, I would really appreciate it. 🙂
thank you.
Is this the DIYHiFiSupply CCS in question?
CCS (Constant Current Source. Super low noise based on 10M45S.) – DIY Hifi Supply
That is a basic single-MOSFET CCS, nothing more.
Makes me wonder what the 6AS7 was for in that 45 preamp posted earlier.
PS - Found it! Tram2 preamp thread, right here on diyAudio:
DHT OTL Linestage - Tram 2
"The current design will grow one more tube, a 6AS7. This will allow us to expand the range of DHT that can be used without major circuit changes. As seen here we can change 2A3 and 45 on the fly."
Not necessary unless you want to start swapping tube types in and out of the thing.
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exactly, thats why i would rather eliminate that CCS, and keep the triode above to do the MU job.
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A 6AS7 would not do a good job as the plate load in a mu follower. You want that to present an infinitely high plate resistance (load) to the lower tube (the 45). The 6AS7 is a low mu triode, so it will present a limited resistance load to the 45.
Getting rid of the 6AS7 and using the 10M45S as the plate load would work better, because the MOSFET has extremely high gain, which is what we want there.
If you want, I can simulate the two alternatives and send you the results. That might take me a little while because the day is starting here...
Getting rid of the 6AS7 and using the 10M45S as the plate load would work better, because the MOSFET has extremely high gain, which is what we want there.
If you want, I can simulate the two alternatives and send you the results. That might take me a little while because the day is starting here...