6au6 line stage a bad idea?

[ryuji]

Ill be rebuilding my amplifier getting rid of all of my 12au7's and 12at7's. I have addressed my gain stages for my main 5 audio channels however my LFE channel still remains to be thought out/designed.

Since im using an silicon style amplifier for my LFE channel i do not need large amounts of gain but i do need a way to balance the magnitude of the channel with my others. Im considering a cathode follower arrangement but have not found many documented cases of using a pentode as an cathode follower. Is there a reason why its not frequently done?

I intend to tune my channels such that 100% at my source is just barely touching clipping on main channels, thus with a matched subwoofer preamp i would only need to adjust master volume on my sound card and not have to fiddle with sub volume level like i do now(nonlinear at the moment with current topology)

Expectations for the b+ is 450 not 500 volts, compensated by different anode resistor choice. This circuit was tested as a single channel and shown to be superior to previous solution:
http://ryujiwarui.com/upload/Pentode-Rev4B.png

[DF96]

I can't see a cathode follower; the 6AU6 stage is a degenerated grounded cathode circuit.

You can use a pentode as CF, just think about g2 AC grounding. It is probably not often done because twin triodes are so convenient.

[SY]

Originally Posted by ryuji

Im considering a cathode follower arrangement but have not found many documented cases of using a pentode as an cathode follower. Is there a reason why its not frequently done?

Generally, the pentode offers a gain closer to unity, but do you really care if it's 0.99 instead of 0.97? Other than that, there's no real performance advantage.

[Eli Duttman]

There's nothing wrong with a pentode cathode follower. The tricky part is that g2 must be tied by a cap. to the cathode.

Read Kimmel's μ stage dissertation. A μ stage is a μ follower with a pentode CF "upstairs".

[ryuji]

Sorry for any confusion but I linked my complete circuit for high frequency channels only for background Information. I have not designed my subwoofer preamp circuit yet. My idea was that with identical tubes matching the channels would become easier.

[DF96]

As any CF has a gain just below 1, any CF will be a reasonable gain match to any other CF whatever valve is used.

[Original Burnedfingers]

There is an Aikido 6au6/5687 line stage. I made one and it sounds nice.

[ryuji]

Originally Posted by DF96

As any CF has a gain just below 1, any CF will be a reasonable gain match to any other CF whatever valve is used.

I did not plan on using a cathode follower on my other channels, however i do still intend/need the preamp on my LFE channel.

Using the same grounded cathode topology and then attenuating it back down to line voltage is a poor choice, So a cathode follower in theory would accomplish my goals?

From a implentation point of view is it as simple as taking my 28~33k resistor in the anode of my other preamp design and bringing it down to after the cathode bias resistor, and changing the 1 meg to join in after the cathode bias resistor? or is that a poor way to design my cathode follower?

As such i would think any nonlinearities would match up with my other tubes, just need an log taper on the input to adjust the balance to where i want (the power amp will not have any kind of volume controls after the preamp)

i would have to also elevate my heaters about 100v to compensate