Phono stage design considerations part 1: choosing 1st stage tube

[SY]

That's an exceedingly odd reading of my post. I wouldn't be as annoyed by this if it weren't for the fact that Allen was a friend with whom I enjoyed quite a few really excellent technical and personal discussions, and whom I miss greatly.

What I did take away from that shootout was that this was an exceedingly poor way to come to any conclusions about electronics. That was also Broskie's take, and he was amusingly sarcastic about it.

 

[TonyTecson]

@ OP, please post the final schematic when you come to it, after all this is a DIY forum....

 

[Joshua_G]

I will. It will take a while.
I may consult in the forum here about few things before finalizing the schematic.

 

[Hilmar53]

Thanks a lot Joshua and Thomas
for your hints about HF-oscillation.
I will try all what you say.
Maybe i get my LCR running.
Thanks,
Hilmar

 

[Adams_Leo]

18ma plate current. It is very high on the list of my favourite tubes for this application, only topped by EC8020 or WE437. I prefer it over E810F, E55L.
I used it with Lundahl LL1692A

Hi Thomas,thanks for you sharing this information,I would like to know which step-down model for the LL1692A to drive the 600 ohm RIAA? I check the LL1692A datasheet,it should be set as SE Line Output 3.5 : 1 /21ma Model,but anyway you suggestion will be great appreciate. thanks

BR
Leo

 

[Adams_Leo]

Hi,
I decided to follow Thomas' suggestion: D3a transformer loaded -> 600R LCR -> D3a.
I've finished considering options for 1^st tube.

Hi Joshua, have you finished this topology LCR phono preamp?would you please share the schematic?thanks

BR
Leo

 

[Joshua_G]

Hi Leo,
No, I didn’t continue this project. I may do it in the future, or I may not - I’m undecided yet.

 

[Adams_Leo]

Thanks Jushua

 

[stocktrader200]

lowest noise transistor you can find then feed a 2 stage 6922 or 12AX7. 6922 easily drives the output. even at 80v p-p driving 25k load 6922 sounds great.

 

[VT52com]

psst, that was 2.5 years ago

 

[mashaffer]

I realize that this is an obsolete thread but it does raise a question about the 6GK5. IIRC it is a semi remote cut-off tube which begs the question how much voltage can we swing before the variable characteristic becomes objectionable.

 

[TheGimp]

I don't see anything in the datasheet about being semi remote cut-off. It is a frame grid tube though.

https://frank.pocnet.net/sheets/049/6/6GK5.pdf

It looks like Mu flattens out between -1Vgk and -.5Vgk (sheet 4). For a small signal amp, that might be a good bias region.

6FQ5 is equivalent, and it does state Semi remote cutoff.

 

[cogsncogs]

I don't see anything in the datasheet about being semi remote cut-off. It is a frame grid tube though.

From Tung-Sol data sheet: https://frank.pocnet.net/sheets/127/6/6GK5.pdf

 

[Johan Potgieter]

R.f. is not my main field, but I do not know of a frame grid tube being remote cut-off. Anyway as said, for a pre-amp it is used as the phono input tube, strictly a small signal application. (To my knowledge the remote cut-off feature only applies for larger signals; at low bias the Vg-Ia slopes are virtually the same for remote and sharp cut-off types.)

 

[cogsncogs]

R.f. is not my main field, but I do not know of a frame grid tube being remote cut-off.

As another example, the 6ER5 is a semi-remote cutoff frame grid triode.

Anyway as said, for a pre-amp it is used as the phono input tube, strictly a small signal application. (To my knowledge the remote cut-off feature only applies for larger signals; at low bias the Vg-Ia slopes are virtually the same for remote and sharp cut-off types.)

Yes.

 

[smoking-amp]

The GE datasheet for 6GK5 gives a good set of curves. Clearly gain controlled or semi-remote cutoff. Looks OK for small signals if you keep it up at 10 mA.

There is the 5JK6 7 pin frame grid pentode with internal Mu of 70, gm 18000. (there is a 6JK6, but those are very expensive and may be polluted with 6JL6 semi remote tubes, there is no 5JL6 fortunately)
The 5JK6 was on the $1 list a while back. I see one for $0.99 on Ebay.

Then there is the 6JC6 9 pin frame grid pentode with internal mu of 60 and gm 16000 which is still on the $1 list.

There is also the 6F12P, gm 19000, Mu 100 for T or P side, 9 pin.