[Niteshade]

6SN7's: TungSol- new and old, RCA, GE, Sylvania and various other vintage brands such as KenRad

The suffix can be GT, GTA, GTB

Matching: Not necessary as sets or per triode within the tube

6L6's: 6P3S-E(Russian 5881), JJ/Tesla 6L6GC, 6L6WXT+, Metal 6L6's

I typically do not recommend expensive 6L6's. The new 6L6's mentioned work perfectly and rolling them is easy with Tunable Biasing.

Favorite upgrade #1: 6L6WXT+ and new issue TungSol 6SN7's. A great compliment to the NS-40.

Favorite upgrade #2: Current issue TungSol 6550's and 6SN7's for the NS-60

Power tubes should be purchased as matched quads.

Preamp upgrade: Current issue TungSol 6SN7's (TBA on web site soon.)

[ProCast99]

Hi Blair:

I realize this is a bit tangential, but I wonder why the two 6SN7s do not need to be matched - what function do they play in the circuit? Do the strengths of the individual triodes make no difference in the signal that goes to the power tubes?

Thanks!

Stuart

[Niteshade]

The 6SN7's do not have to produce allot of power and are loaded lightly. Good, healthy tubes always work perfectly because of the no stress situation. There is not enough of a variation between in-spec tubes to make any difference.

In my amplifiers, the 6SN7 is used as a voltage amplifier and phase splitter (there is no phase splitter in single ended designs). The voltage amplifier increases signal strength from the input RCA's to a level acceptable to the splitter, which has no gain.

A sine wave has a positive and negative side. A sine wave travels 360 degrees total, including a crossover point where the voltage is zero. The phase splitter is designed to split the 360 degree waveform into two 180 degree sections. One half goes to one power tube while the other half goes to the one beside it. This is called push-pull amplification.

[ProCast99]

Thanks for the great explanation Blair - may I ask one follow-up question, then - if the 6SN7s are working as both voltage amplifier and phase splitter, is one tube doing the amplification, the other the phase-splitting (i.e. they are working in series?) ?

If so, I'm guessing one triode in the 6SN7 takes one phase, the other takes the other - and do they pass them onto one pair of power tubes per triode (I have an NS-30)?

Have I understood correctly, or is there something else going on?

Thanks!

Stuart

[Niteshade]

A 6SN7 is a dual triode. Both triodes are completely independent. For each channel, 1/2 of a 6SN7 acts as a voltage amp while the other half is working as a splitter.