V1 split cathode

[Kee22]

Whats the benefits of a split cathode in V1 on a bassman micro variant?

[maxkracht]

Less interaction between channels and ability to bias each preamp differently and/or use different cathode bypass caps. If you do this, remember to double the cathode resistor value if you want everything to remain the same. Shared 820R = single 1640R, 1k5 being closest standard value.

[Kee22]

Can't get my head around this V1 seems like and odd solution. Pin 1 100k 0,022uf, pin 2 68k, pin 3 820 ohm 22uf.

[johnnyreece]

Sounds like pretty standard values. Pin 1, plate resistor and coupling cap; pin 2, grid resistor; pin 3, cathode bypass cap and resistor (although, since it's only 1/2 of the tube, I'd double the resistor to 1.5k-ish, as was mentioned earlier). The other triode is unused in this configuration.

[sluckey]

Can't get my head around this V1 seems like and odd solution. Pin 1 100k 0,022uf, pin 2 68k, pin 3 820 ohm 22uf.

Thousands of amps look exactly like that. Doesn't get any simpler. What don't you understand?

[Kee22]

The builder said (not me) it was a split cathode V1 but as was pointed out it only use one side. Just needed the confirmation.

[maxkracht]

The builder either didn't understand how it worked or purposely chose to bias that stage hotter. If there is only one channel, it's not necessary to use the other half of the tube.

[johnnyreece]

In the typical bassman micro, V1 is paralleled. Wouldn't be hard to implement that here. Just 3 little wires...

[Kee22]

Your right there's only 1 channel but why do you add this extra lead from pin 3? Ground wire? The lead to the left is from pin 3, resistor is 2,7K.The other picture is the old board from above. Still learning but making progress.

[maxkracht]

Looks like the cathode bypass cap is backwards, is there a picture of the complete build or are you still building it? Pin 3 is the cathode, if there's an extra lead maybe it is a shared cathode on another stage. Do you have a schematic/layout?

[Kee22]

The bypass cathode is correct because the leads are reversed. No I don't have any documents or schematic that's whats make it so hard to for me. I will continue to try and figure out the circuit. I know its based on a bassman with some tweaks. Fixed NFB, balanced bias, single channel, bass, middle, treble tonestack, bright switch, dual 6l6 output, diode rectifier.

[maxkracht]

I don't see any extra wires on your tube socket picture. Do you have photos of the completed amp or is it still in pieces? You should make a layout and/or ask whoever built it for details. If it's push pull 6L6 it's not micro. Take a 5F6A schematic/layout and annotate the differences.

[pdf64]

Rather than just isolted photos of just the board or V1 socket, it may be helpful to provide photos that add up to provide a complete picture of what you're got there.

Whatever, as only half of (what I assume is) the V1 socket has ever been wired up, it seems that it's a single channel amp, probably with only 1 or 2 input sockets.
As such, the split cathode thing for V1 doesn't apply, as only 1 of its triode cathodes is being used.

[Kee22]

The problem is that the amp is in pieces at the moment and its not possible to get in touch with the builder, I've tried. These fotos are from the original layout hope it helps. Any pointers you guys can give me is much appreciated.

[maxkracht]

Looks like the last guy mirrored an existing layout, might make more sense flipped upside down. Maybe it never worked properly and that's why it's in pieces?