• 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.

tube question

5670, a very nice 5 Star tube.

Are you worried about the channel to channel separation degradation of a dual triode?
Then I hope you are using high separation signal sources, such as CD, etc. (and also only high channel separation recordings too).
Peel the outer layers off of the onion, before getting to the inside core.

Consider a lot of good phono cartridges, even when they are set up very accurately:
25dB - 30dB @ 1kHz
15dB @ 100Hz
15dB @ 5kHz

I designed and built a single ended stereo amplifier using type 45 output tubes.
There was only a single 6.3V filament winding, so I used series resistors on both legs of both filaments to get 2.5V.
But that also required a common self bias resistor (820 Ohms).
Two 25 Ohm resistors were connected to the parallel filaments, and the other ends to the 820 Ohm self bias resistor and 1000uF bypass cap.
That resulted in an Intrinsic channel separation of "only" 40dB across the 20Hz to 20kHz audio range.

What, only 40 dB of channel separation? What could be worse?
Oh, did I mention that nobody said anything about the "bad channel separation", and they all liked that amplifier that I played at work (with a pair of Usher S-520 speakers).

Just My Opinions, and Just My Experience

If you want to know a little bit about channel separation, please look at some of your CD recordings on an XY display.
If it does not spread and have "bloom", then there is very little channel separation (low channel separation looks like a thin line with only a little line width).
Warning: You might now be disappointed with some of your favorite recordings!

Lighten up a little, and "Enjoy The Music"!
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i am rebuilding my pc audio system (2.1ch) using an m audio 2496 hd card. i want a dual mono tube preamp to drive my rotel rb850 dual mono amp. found schematics for an amp that uses a single 5670 dual triode but wish to have completely separate channels after audio card. sub is driven by another rotel rb930 ax.the rotel rtc-850 that is the preamp now needs replacement