Questions on JE Labs transformer coupled line stage

[Glowbug]

So I'm thinking about building the JE Labs transformer-coupled design with a single 6SN7 instead of the 76s.

An externally hosted image should be here but it was not working when we last tested it.

I found this thread on here, http://www.diyaudio.com/forums/tubes-valves/92610-transformer-coupled-linestage.html...I've heard good things about James OPTs, so I'm tempted to try them for this project. Problem is, I can't find JS-3004Ns anywhere.

TC Tubes - specializing in vintage vacuum tubes that place has some of the James line, but not the preamp coupling ones. I'd like to get an idea how much they cost, so I know if this project is in my budget or not - $250 a pair is OK, $400 is not

Are there any other brands that would be recommended? One Electron, Magnequest, Lundahl? I saw some Lundahl ones at K&K Audio's page, but it was hard deciphering what the primary/secondaries were...

I have more questions, but that's all for now Thanks.

 

[kevinkr]

I can recommend both Magnequest, and Electra-Print for their plate to line transformers.. Another good option could be the UTC A-25 (eBay) as long as you keep current in the 6mA region.

The 6SN7 (consider 6C5/6J5 as well) will give you more gain than the 76.

 

[Glowbug]

Thanks.

Is there a significant difference between the "regular" and nickel-core Magnequest ones?

 

[dsavitsk]

Is there a significant difference between the "regular" and nickel-core Magnequest ones?

Nickel is generally higher permeability and lower distortion. It is definitly better when there is no DC on the core. But, with DC it will saturate more easily requiring a larger core, eliminating some or all of the benefit of higher permeability. Some people still like it better (Magnequest), and some think it a waste in this application (Electra Print).

FWIW, I think the rp of the 6sn7/6j5 is a little high for transformer coupling. I think I'd use a 6H30, 5687, 6922, ecc99, d3a, etc. instead.

 

[Glowbug]

Good to know, thanks

I think I'd use a 6H30, 5687, 6922, ecc99, d3a, etc. instead.

If I went with the 6922, how would that change the other circuit components?

 

[mwiebe]

Jim,
I’m listening to a pre-amp like you’ve drawn (without the bypass cap and 600 ohm cathode resistor) through an Electra Print L3500 (10K/600--you can order headphone taps if that appeals). A pair will set you back $212 if the website is up to date. 10K is not what I would pick for a 6SN7 but in practice it works just fine. I have plug and play power supplies, 250V, 150V, 30V battery, and lots of different tubes, subminiatures and 7- and 9-pins wired to octal plugs, so I’m a tube rolling fool. Just build what you plan and have fun.
Matt

 

[revintage]

Hey Jim,
If you go for 6922 you will need a 4:1 transformer with at least 100H primary. You could run it at ca 10mA/150V Ia/Ua.

Why not let Dave Slagle at intact audio design and customwind a pair for you?

 

[ourvacuumtube]

So I'm thinking about building the JE Labs transformer-coupled design with a single 6SN7 instead of the 76s.

An externally hosted image should be here but it was not working when we last tested it.

I found this thread on here, http://www.diyaudio.com/forums/tubes-valves/92610-transformer-coupled-linestage.html...I've heard good things about James OPTs, so I'm tempted to try them for this project. Problem is, I can't find JS-3004Ns anywhere.

TC Tubes - specializing in vintage vacuum tubes that place has some of the James line, but not the preamp coupling ones. I'd like to get an idea how much they cost, so I know if this project is in my budget or not - $250 a pair is OK, $400 is not

Are there any other brands that would be recommended? One Electron, Magnequest, Lundahl? I saw some Lundahl ones at K&K Audio's page, but it was hard deciphering what the primary/secondaries were...

I have more questions, but that's all for now Thanks.

Hi, I have 15K to 600 plate to line but Plate current is limited to 6-8mA (UTC A-25)
Is this schematic OK with my line transformer ? How if I apply fixed bias at Vp=180V and -5/-6 at Vg

Anyone can help ? Any comment wuld appreciated

ThANK YOU
jj

 

[lt cdr data]

hi glowbug, obviously, I would stick with tx's that are home grown, simply as they are heavy, and will be expensive to ship from abroad.

unless its a mega project, I wouldn't spend a fortune and go with decent tx's apart from hi end ones, try hammond groan, or from abroad, pat turner from australia who's amazing. sowter's, silks, also if you wish to import, and also holland's AE are very good, but best home grown considering price really. james are good. tbh I think commercially, all are ok myself, have tried cheap and dearer and don't think dearer are worth cash reallyl. chinese were fine for me. obviously custom wound better tho' as bespoke.

lundahl's, yes but again, I find them impossibly complex. perhasp stick with edcor/ james/ slagle/ one electron