• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6V6 line preamp

diyAudio Chief Moderator
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It was 28mA with ducking B+ already. Those old Ruskies bias strong and near together, good. So, check if it really was something wrong, and push it again by 5mA steps if not. In case its just the JFET IDSS in the reg that can't give more than 300V while you get more CCS after a point, it can be remedied and not a real problem right now. All we need to know is where the valves bias and allow 20mA plus on total.
 
so I'll try from 60mA to see if I can get 340V .. then 65mA .. and so on ?

I think I'll do this tomorrow Nick, already a bit sleepy and HV isnt a piece of cake for me ,

I'll get a nice sleep and tomorrow i'll check again all joints/grounds, maybe I'll change those output caps with some K75 that I've got ... and see what happens .....
 
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I want to try the 6V6 line preamp but I have SS power amps with low input impedance so first to make the preamp I have several questions:

-Input impedance
-Output impedance
-Gain
-If needed what specs have to have the output transformer
-Cathode resistor bypassed with cap can be replaced with LED, if yes wich value in volts?
-If used the mod for B+ 300V and plate resistor 7K5, have I to change the cathode resistor & the cap value?
 
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-If used TVC at the output after the output tx, what input impedance will remain?
-If I use output tx no need the output cap, right?
-Wich secondary value for output tx 600 ohms or other value for a SS amp? wich power in mA have to be rated? wich kind of material? suggested brands? or better order a special tx with the necessary specs?
-Can I use only one power transformer fopr B+ & heaters?
 
diyAudio Chief Moderator
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Good luck.
 

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diyAudio Chief Moderator
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It will take a 50W metal body plate resistor on proper sink with good thermal paste and ventilation so to take 18.6W well in the long term. With such B+ and high ohmic load the linearity kicks up of course. About minus -78dB second harmonic to dB full scale.

P.S. The 6V6 itself will dissipate just 7W.