But why do you want to drop 20V? 4V is enough to put the E81L in the 10mA area with a grounded grid resistor. You could run the output stage at 10mA with 400 ohms total DCr, which is just adding 60 ohms in the cathode.Replacing parafeed choke with SE Trafo. A resistor in series with the transfomer mimicks higher dcr. Right. If we look at the v74 it has a 45H choke, dcr ca. 1k in the line stage. If a add a 670ohm resistor i series with the LL1671 (total cdr 1k) it will drop 20v at 20ma.
I re-read your earlier post and I get what you mean, the choke can swing negativeBut why do you want to drop 20V? 4V is enough to put the E81L in the 10mA area with a grounded grid resistor. You could run the output stage at 10mA with 400 ohms total DCr, which is just adding 60 ohms in the cathode.
Yep I missread u I like your simple solutionBut why do you want to drop 20V? 4V is enough to put the E81L in the 10mA area with a grounded grid resistor. You could run the output stage at 10mA with 400 ohms total DCr, which is just adding 60 ohms in the
great to hearI rebuilt a small guitar combo a while ago and used an output stage exactly like you have drawn right now, albeit with a russian 6E5P output tube. I actually had to apply some positive bias to the grid because the output transformer's DCR put it too far negative. Just wanted to affirm you in your plans, it should work out just fine .
Why? You don't need voltage across a xfmr for it to work. You need current. In what is it different than putting the same xfmr in the anode?
I agree you need some DCR for cathode-bias to work. The datasheet shows perfect adequacy.
Yep this little planar tubes really got some super power and I think its the combination. Low noise and microphonics combined with very high gain and voltage headroom. They were build to survive the enviroment of rocket noise con... But Glen Miller made them turn down the trebleTheres a kind of a cross polination in several recent preamp threads going on , its no reason for appologies and its all good food for thought at the end of the day .
Disc seal RF triodes Ive long wondered about usage in audio , I see now the high gain naturally means 'Miller effect' becomes an issue at high frequencies .
Grounded grid /fet driven cathode looks good though.
Could the 6C45Pi be the native compatriot to a 6s17k-v front end ?
Im liking the power hungry and costly iron pre topologies that have come into the convo of late , you only need a channel or two for vocals and lead acoustic instruments in an overdub situation either way , its not the end of the world if you throw away a few extra watts off the anode ,
now were suckin' diesel
The main 'problem' with the cascode is that the top tube represents a much lower impedance load to the bottom tube than the usual plate resistor. The voltage gain of the bottom tube is therefore very low, which is why Mr. Miller is not a problem, but this lower than usual load is also what creates the distortion.
Hi Winston, I agree those distortion figures are not bad at al and as you say very triode like. Can you remember which tube this was? Was this unloaded?
Interesting circuit. Reminds me a lot of Rupert's tube pre with an EF86 first stage followed by a CF which drive the EF86 screen grid in almost exactly the way you derive to cascode top grid voltage.
I am pleased you were trying to encourage me too try a cascode. I admit I have not built any but I have simulated one to find out how good the distortion is and it was not very good. But I will check it out again.