Tube DIY Asylum

We split phase with a tube....Can we sum to mono with a tube?

76.174.175.12

Iczerman

I figure...
Using 12at7..
Paralleling cathodes..so cathode resistor is cut in half.
Left and right channels go to each grid with appropriate grid resistors.
Plate load resistors are calculated for one plate for each triode.
I'm thinking that I can join the two plates BEFORE the coupling capacitor.
Or...
Should I use 2 coupling capacitors and resistors to ground and join them at the grid of the power tube?

I know I'm crazy...but it's a matter of scale. ;)

Follow Ups:

Input isolation? - Triode_Kingdom 13:59:46 02/20/24 (0)
If the application doesn't require isolating the left and right signals from each other at the input of the combiner, just use a couple high value resistors like Chip647 suggested below. If it's necessary to prevent the right and left from mixing ahead of the stage, you could use a two-channel active mixer. Here's one from the RCA Receiving Tube Manual RC-21 (p. 460). Note that the 6EU7 is identical to a 12AX7, but with a different pinout. Change the two pots to fixed 100K resistors and use Input 1 and Input 2 for left and right:
- RCA RC-21 PDF (Open in New Window)
Just becase you can does not always mean you should - Chip647 12:04:53 02/20/24 (0)
Just use matched 1K to 10K resistors from each input to a common tube grid..
Then use the tube to buffer/amplify the mono signal.

You could use a twin triode and join the cathodes, then put one channel on one triode and the other on the other. Then you could take the common output from the joined cathode follower. It will be a worse solution compared to the resistor join though because matched resistors will have far less distortion on the summed signal than using tube sections for that function.
RE: We split phase with a tube....Can we sum to mono with a tube? - PakProtector 05:42:42 02/20/24 (0)
Try defining what exactly makes a stereo recording. Can you sum this signal like you suggest? I am going to bet 'NO'...

But it might help if you look up a tube summing amp circuit so as to give yourself a starting point.

Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
RE: We split phase with a tube....Can we sum to mono with a tube? - Cleantimestream 05:06:32 02/20/24 (0)
Is your aim to cut the plate impedance in half? Use a superior tube ....when we do it ourselves we are able to use rare superlative tubes ie. 8608 there are others as well.
I don't understand your rational/goal. Decouple? Reduce noise?
The Mind has No Firewall~ U.S. Army War College.

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