salas said:
I was thinking about this one: http://www.diyaudio.com/forums/showthread.php?postid=1690784#post1690784
But reading more, I think you are correct about his purpose. I'd be surprised, however, if it didn't change the spatial impression, as well as even out bass response.
Sheldon
rjhanauer said:Hi i am very interested in this Thread and ordered 4x 1J6G
Tubes so i can Judge for myself
Has anybody got the Circuit for this Tube
Thanks RUDI
1J6G:
http://www.mif.pg.gda.pl/homepages/frank/sheets/084/1/1J6G.pdf
This is a draft version from a colleague, used in single ended mode. My own is balanced and has the stepped attenuator and 7.5k resistor directly soldered to the grid of the 1J6. My own version doesn't have the glow tube, but has an AZ1 mesh, 2uF cap polypropylene, 10H choke and 50uF polyprppylene cap. - andy
Attachments
Couple of other things - in my version the stepped attenuator is 12 step 47k in shunt between the two grids, so there's an input resistor to earth before the 7.5k in series - 250k or whatever you fancy.
The 1J6G should have matched halves to eliminate DC in the 124b. You really need a tube tester or something like that to match the halves. In my stash of 1J6G about one third were pretty good matches, and less than that were really good matches. They're not terribly expensive like the usual DHTs. I used it because I wanted a balanced input, so a double triode with common cathode was a good choice and meant a less complex filament supply. For that I used 6-0 6-0 toroid, SChottky diodes, 15,ooouF cap, LM1086 as current source with 5.2 ohms resistor, 1 watt, connected between adjust and out, with positive output from adjust pin.
andy
The 1J6G should have matched halves to eliminate DC in the 124b. You really need a tube tester or something like that to match the halves. In my stash of 1J6G about one third were pretty good matches, and less than that were really good matches. They're not terribly expensive like the usual DHTs. I used it because I wanted a balanced input, so a double triode with common cathode was a good choice and meant a less complex filament supply. For that I used 6-0 6-0 toroid, SChottky diodes, 15,ooouF cap, LM1086 as current source with 5.2 ohms resistor, 1 watt, connected between adjust and out, with positive output from adjust pin.
andy
Gents,
I find the whole argument pretty much pointless if the source is an op-amp laden CD player. 99% of systems have enough poweramp/speaker gain not to need a preamp when hit with 2 VRMS, so it is there as a flavour additive in most cases.
Now if you are building a REAL preamp, one that is intended to amplify a phono cartridge or a tape head, then we can really start discussing things of importance.
I for one am not willing to do a DHT phono stage, but I have heard one or two and they are pretty good, but normally have far more iron than I like to use.
Regards, Allen (Vacuum State)
I find the whole argument pretty much pointless if the source is an op-amp laden CD player. 99% of systems have enough poweramp/speaker gain not to need a preamp when hit with 2 VRMS, so it is there as a flavour additive in most cases.
Now if you are building a REAL preamp, one that is intended to amplify a phono cartridge or a tape head, then we can really start discussing things of importance.
I for one am not willing to do a DHT phono stage, but I have heard one or two and they are pretty good, but normally have far more iron than I like to use.
Regards, Allen (Vacuum State)
Gordy said:
Similar u (about 15) and transconductance, but lower power in a 7 pin bottle. Also inexpensive: http://www.mif.pg.gda.pl/homepages/frank/sheets/049/3/3A5.pdf
Sheldon
Allen Wright said:
http://www.geocities.com/dmitrynizh/3a5-phono.htm
Check out the plate curves.
Sheldon
Gents,
I find the whole argument pretty much pointless if the source is an op-amp laden CD player. 99% of systems have enough poweramp/speaker gain not to need a preamp when hit with 2 VRMS, so it is there as a flavour additive in most cases.>>>
To Allen Wright - I should have said this, but preceding my preamp is a RAKK DAC - this is a low output DAC since it's current output and the i/v resistors from each leg to earth are 75 ohms. There's no op-amps after the DAC - the output with DC on it goes straight into the grids of the 1J6G. This then gets equalised in the biasing of the 1J6G. So really for "preamp" you could substitute "DAC tube output stage". That's true of the last bunch of preamps I've built - they all work straight out of a RAKK board.
But as others have said - a preamp is nothing but an amplification stage, whatever comes before it. I don't know if you'd call mine a "real" preamp - it has to bring the voltage up from about half a volt to a bit under two volts if you include the stepdown in the output transformer. I can see that a commercial designer like Allen, or indeed Kevin with the RAKK would not want to build with extinct tubes, against which it could be said that there a plenty of stocks of some of the DHTs like 26 and 01A. Transformers add money - OK for Kevin as an importer at least. And I know that in his own systems Kevin uses 01A, 26 and no doubt many more. So you may want to play around with some DHTs, Allen, even if they don't go into products.
Other points - the 3a5 is another good double DHT - I've used that for preamps as well. I think the 1J6g is probably better.
The 6J6 comparison eluded me - I was thinking 6J7. I don't think there's much of a comparison, certainly not in terms of sound - they're worlds apart.
As for headphones - I don't have any good ones. It's a very interesting point. I should see if I can borrow some.
andy
I find the whole argument pretty much pointless if the source is an op-amp laden CD player. 99% of systems have enough poweramp/speaker gain not to need a preamp when hit with 2 VRMS, so it is there as a flavour additive in most cases.>>>
To Allen Wright - I should have said this, but preceding my preamp is a RAKK DAC - this is a low output DAC since it's current output and the i/v resistors from each leg to earth are 75 ohms. There's no op-amps after the DAC - the output with DC on it goes straight into the grids of the 1J6G. This then gets equalised in the biasing of the 1J6G. So really for "preamp" you could substitute "DAC tube output stage". That's true of the last bunch of preamps I've built - they all work straight out of a RAKK board.
But as others have said - a preamp is nothing but an amplification stage, whatever comes before it. I don't know if you'd call mine a "real" preamp - it has to bring the voltage up from about half a volt to a bit under two volts if you include the stepdown in the output transformer. I can see that a commercial designer like Allen, or indeed Kevin with the RAKK would not want to build with extinct tubes, against which it could be said that there a plenty of stocks of some of the DHTs like 26 and 01A. Transformers add money - OK for Kevin as an importer at least. And I know that in his own systems Kevin uses 01A, 26 and no doubt many more. So you may want to play around with some DHTs, Allen, even if they don't go into products.
Other points - the 3a5 is another good double DHT - I've used that for preamps as well. I think the 1J6g is probably better.
The 6J6 comparison eluded me - I was thinking 6J7. I don't think there's much of a comparison, certainly not in terms of sound - they're worlds apart.
As for headphones - I don't have any good ones. It's a very interesting point. I should see if I can borrow some.
andy
Thanks for publishing this interesting circuit Andy. A couple of offtopic questions:
Is the 124B really good enough to do justice to a Vishayed Shallco? What can you compare it to? Would it have any bass with demanding music?
Worst case input impedance seems quite low. Was it primarily intended for use with digital sources?
Thanks.
Is the 124B really good enough to do justice to a Vishayed Shallco? What can you compare it to? Would it have any bass with demanding music?
Worst case input impedance seems quite low. Was it primarily intended for use with digital sources?
Thanks.
Thanks Gordy and Andy for your replays
Not only in PriAmps i build PSE EL34 and 6550 PSE
Power Amps den came PSE 300B and i fond the same
as Andy derwas more realistic Music with real People
singing and as Andy says Timbre of Instruments
sounds more true IMHO and most People who listen
to my setup this is why i like to build DHT Pri Amp to judge
if i get same result as with Power Amps.
In the meantime i read this interesting Debate
Rudi
Not only in PriAmps i build PSE EL34 and 6550 PSE
Power Amps den came PSE 300B and i fond the same
as Andy derwas more realistic Music with real People
singing and as Andy says Timbre of Instruments
sounds more true IMHO and most People who listen
to my setup this is why i like to build DHT Pri Amp to judge
if i get same result as with Power Amps.
In the meantime i read this interesting Debate
Rudi
Andy,
AOK on your RAKK CD player. Great to hear this!
Then my point is irrelevant WRT to you, but not in the other 99% of people posting here with weird amp designs, all played through a opamped CD player.
Better dig out those 1Q5's I started my whole elctronics trip on, used in one valve regenerative radios...48 long years ago.
Regards, Allen (vacuum State)
AOK on your RAKK CD player. Great to hear this!
Then my point is irrelevant WRT to you, but not in the other 99% of people posting here with weird amp designs, all played through a opamped CD player.
Better dig out those 1Q5's I started my whole elctronics trip on, used in one valve regenerative radios...48 long years ago.
Regards, Allen (vacuum State)
Hi Andy,
Have read your threads with great interest. So now I must have a try as hearing is believing
.
One can look at both 1J6G and the dirt-cheap DCC90/3A5 as dual plate DHTs and use one /channel. This halves Ri and doubles Gm. 3A5 being interesting due to the possibility to use a 1,5V-cell for heating. Of course the triodes have to be selected with matched halves.
Below is how I am going to do it. My friend Hoktuna has almost the same circuit with 417A/5842 so I think it will be an interesting challenge......
Have read your threads with great interest. So now I must have a try as hearing is believing
. One can look at both 1J6G and the dirt-cheap DCC90/3A5 as dual plate DHTs and use one /channel. This halves Ri and doubles Gm. 3A5 being interesting due to the possibility to use a 1,5V-cell for heating. Of course the triodes have to be selected with matched halves.
Below is how I am going to do it. My friend Hoktuna has almost the same circuit with 417A/5842 so I think it will be an interesting challenge......
Attachments
There are a few cheap DHTs you can experiment with. 1J6G and 3a5 are good in the double triodes - didn't have much luck with the 3B7 - anyone like that one?
And a few good cheap single triodes. The 31 is a favourite - very musical. 01A is superb, so is 26. Both plentiful and perfectly fine in the ST shape.
Plenty to get started with. If you haven't tried any of these - push the boat out and have a go! I started with a bench power supply for the heaters before learning to build filament circuits, which actually is dead easy when you've done it.
Andy
And a few good cheap single triodes. The 31 is a favourite - very musical. 01A is superb, so is 26. Both plentiful and perfectly fine in the ST shape.
Plenty to get started with. If you haven't tried any of these - push the boat out and have a go! I started with a bench power supply for the heaters before learning to build filament circuits, which actually is dead easy when you've done it.
Andy
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