• 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.

Stereo class A 6+6W - 2x 6L6G 1 x 6N2P

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#22
Corrected schematic:

note: I increased anode resistor of 6N2P from 47k to 56k (small gain adjustment) but if feedback is used I'd suggest to increase it up to 100k.

comple15.jpg


partic10.jpg
 
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#24
With UL in this setup, what would the effect be of changing the value of the screen resistors? Is dropping the screens below the plates the major consideration? Is it merely a tradeoff between power and safety? I ask because I think I've generally seen lower screen resistor values on UL and I'm ignorant on UL's considerations.
 
#25
jjman said:
With UL in this setup, what would the effect be of changing the value of the screen resistors? Is dropping the screens below the plates the major consideration? Is it merely a tradeoff between power and safety? I ask because I think I've generally seen lower screen resistor values on UL and I'm ignorant on UL's considerations.
Click to expand...

6L6 screen grid should not exceed 250V, this circuit has 290V plate voltage, the screen resistor is calculated for 50V voltage drop.
 
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#28
jjman said:
With UL in this setup, what would the effect be of changing the value of the screen resistors? Is dropping the screens below the plates the major consideration? Is it merely a tradeoff between power and safety? I ask because I think I've generally seen lower screen resistor values on UL and I'm ignorant on UL's considerations.
Click to expand...

pilovis said:
6L6 screen grid should not exceed 250V, this circuit has 290V plate voltage, the screen resistor is calculated for 50V voltage drop.
Click to expand...

270V is the max screen grid voltage for old 6L6 types, like the original metal can ones, or 6L6G, 6L6GA (from RCA Tube Manual).

The Tung-Sol 6L6WGB was rated for 300V on the screen grid (grid #2).

6L6GC can take 500V (!) on the screens "in push pull circuits where the screen of each tube is connected to a tap on the plate winding on the output transformer." (From GE Tube Manual)

So, with screen voltages above 300V, use a 6L6GC.

The screen grid resistor in a UL connection is a "screen stopper," is it not? It's not a decoupling resistor with a filter capacitor. The screen stopper goes from the screen grid to the 40% tap on the OPT. 2k2 is a large value in this spot, but I don't think it does any harm for it to be a large value. You could try the more usual 470R and see if it makes any difference at all.


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