Cathode Follower ideas please.....

[losacco]

Looking for a 6SN7 cathode follower line stage. Need power section also.
Thanks.....

[SY]

Why 6SN7? That's not a super tube for CF service. What's the application?

[Miles Prower]

What is it, exactly, you want the cathode follower to do? Do you need to source some serious current to deal with the capacitance of long cable runs? Is it more impedance matching?

Depending on what it is you're doing, 6SN7s will work just fine for cathode follower duty. I've used these myself to make grid drivers for the finals. since these designs were Class AB1 pentodes, capacitance and grid current demands weren't severe, as pentodes tend to be quite easy loads. Otherwise, the 6SN7 has a rather high dynamic plate resistance (~6.0K) and that can put a limit on drive capability.

As for possible designs, you can go with either a passive tail load, or an active load. The latter will definitely help with distortion reduction and maximizing output swing.

Finally, never forget that the main purpose for a cathode follower is to present a Lo-Z source to a Hi-Z load. Just because it has a Zo= 300R, for example, doesn't mean it can drive a 300R load.

[DF96]

6SN7 have too low a transconductance to make a good CF - they work best as CF in situations where you don't really need a CF, such as a 'tube buffer'.

[bigwill]

The best CF is a MOSFET source follower, you even get to save a tube!

[Brit01]

The best CF is a MOSFET source follower, you even get to save a tube!

But where's the fun in that?

I just built a nice little CF as a buffer between my cdp and power amp.

Direct connection just sounds bland.

I'm using a tube power suppy and a 6H6P with a bootstrap config.
Alps 10K pot and Auricap coupling caps.

I'm happy to say the least.