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Re: Maybe use both?

4/17/2004 5:11 PM
Re: Maybe use both?
To get ride of the noise, use a single triode for the first gain stage and leave the second one unused. Elevate the heater voltage or go DC on the first tube.  
6sl7s in my experience are noisy in LTP Pi's but silent in concertina Pi. This is purely my experience, no theory involved.  
I have 20 red base 5691´s and all are dead quiet with the above setup.  
4/19/2004 5:49 AM
Preamp ideas, Dr. KT88?
I've been playing around with 6sl7s as well and (through experimentation) came to the same conclusion as you; for the first stage you can only use one 1/2 of a 6sl7 and leave the second one unused.  
Could you give us any addt'l ideas regarding the R&C values you used for your preamp and voltages. I am not a theory guy, just a trial-and-error type and it has been quite a battle with these tubes as I have not found many schems to my liking.  
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4/19/2004 7:30 AM

Power rail:  
300-0-300 into a GZ34-47uf-4k7-47uf-5k-22uf-47k-22uf  
47uf to the power tube anodes  
47uf o the screen grids  
22uf to the PI  
22uf to the Pre Amp  
100k plate Resistors for the preAMP  
1k2 Cathode Resistors  
47K for the PI anode and cathodes, 1M to ground for the grid of PI plus 2M2 paul C mod.  
0.047uf to the volume, everything else like normal 5E3.  
not a vintage 5E3, but tweaked to my guitar.  
try a 5h choke instead of the 4K7.
4/20/2004 12:01 PM
Rocket Why ?
Why do the tubes become noisy if both triodes are used?  
Can the second triode be used for a second input stage? Or "later" in the amp (3rd, 4th Stage, PI).  
Is it any use to connect the triodes in parallel?  
What about cathodyne input stages, using both triodes?  
And at last: what about the 6SN7 - same problems?  
I was thinking of 4 low gain stages with 6SN7s followed by a 6SL7 PI and 2 6V6 PP powertubes.
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