Singe Channel Plexi pre

[johndandry]

If I'm going for a single channel plexi style pre, what needs to be done with the mixing resistors. Do I keep the volume control- 470k- next tube grid? Or do I need to add a 470k to ground where the old channel would have connected?

Also on V1, would it be possible to do a single input with a common plate and grid but split the cathode and have on with the standard Marshall 2.7k/.68uf and the other an 820ohm/100uf to get closer to the sound of linking channels?I know there is also the coupling cap and cap across the mixing resistor that contributes to the difference in the channels but maybe some advantage to this parallel input stage.
Thanks!!!!

[statorvane]

I don't get it. How are you going to have both bright and normal CkRk on one cathode? Are you going to switch between the two? That is certainly possible. Mixing the two simultaneously - you'd have the equivalent of 630R and 100.68 uF.

[Reeltarded]

Yes on the mixer.

What is it you are after, exactly?

[10thTx]

The original Marshall was a copy of the 5F6-A Fender Bassman. So, it had this large cap on V1-3 cathode for the bass guitar.

Anything above 22uf on V1-3 is pretty useless for guitar (vs. bass) and is just going to add "mud" to the tone, IMO.

So, you could do this idea parallel 2.7k & 1.2k = 830R
................. and parallel .68 & 22uf = 22.68

Just use a spdt switch.

You could consider paralleling V1 for 30% gain and NO increase in floor/idle noise. To do that, just half the 100k plate value and use 56k (close enough). Just an idea to consider.

With respect, 10thtx

[Roe]

If I'm going for a single channel plexi style pre, what needs to be done with the mixing resistors. Do I keep the volume control- 470k- next tube grid? Or do I need to add a 470k to ground where the old channel would have connected?

yes, add a resistor to ground. just add a voltage divider with 270k resistors or 470k resistors (and 500pf cap). Connect a 1m pot if you want to.

[xtian]

I found that keeping the normal and bright channels but jumpering them internally, and reducing the number of input jacks to two (or even one, because I never use the "Low" input) to be a great solution. The mix of normal and bright channels (by simply adjusting their respective volume knobs) provides so much tonal variation that I rarely move any of the tone stack controls away from noon!

See my builds: https://tubeamparchive.com/viewtopic.php?t=19042

[guitardude57]

That is what I have done, internal jump, one input then a volume for each side of the tube. You could there for, pick how each half of V1 is configured to have 2 different preamp sounds... then separate or blended.

I definitely like Jeff's idea paralleling V1 too.

[statorvane]

Sorry, I misread your note - I thought you were referring to V1A only. I see you want to parallel then mix them internally.

Others have good suggestions for the biasing. For mixing, I'd keep separate gain controls. It really gives you a ton of versatility - like xtian said he fiddles more with the gains than the tone controls. I know exactly what he means.

[johndandry]

Thanks for the replies guys! I'll mess around with the cathode and see what I like. I will probably have some more questions soon.