Alembic F2B build 6N1P

[Matador]

I'm assuming you just misnumbered? As it stands, you have cathodes connected to B+ and plates to the 1.5K cathode resistors...

Also there is strangeness in the final tube, as it looks like you have the cathode of one stage driving the plate of the next.

The 100nF leading to the unbalanced out isn't needed in the first diagram.

 

[Spencerleehorton]

Yes I didn’t think that 100nf was needed but did see it as an option in another schematic, got mixed up.
And yes I misnamed the tube numbers!!
The cathode to the plate connection I though was weird but I’m sure it’s like that on the schematic?

 

[Spencerleehorton]

You can see here the cathode pin 8 connected to plate pin 1
This is how I’ve got it wired at the moment!!!

 

[Spencerleehorton]

Hopefully this looks a bit better!!

The other schematic I posted before this could be some errors, taken from another site about a Alembic f2b build.

 

[Matador]

That wiring in post #43 is non-sensical. The one on the noisemikers site makes sense but is different:

 

[Matador]

Oh.....disregard. The way that schematic is drawn makes my head hurt. It looks like maybe they added a WCF stage to drive the transformer.

 

[Spencerleehorton]

Oh.....disregard. The way that schematic is drawn makes my head hurt. It looks like maybe they added a WCF stage to drive the transformer.

yes to me it looks a bit of a muddle and i want to simplify, does my CF drawing look ok and will 100nf cap after it be ok for a step down txf of about 5:1 or 6:1?

 

[Spencerleehorton]

Ah i see now, white cathode follower, better for low impedance, more efficient and cleaner waveform.
i'll leave it how it is and move the master volume to the correct place.

 

[Spencerleehorton]

I did wonder about the value of the end cap 2.2uf into the 5:1 transformer as on other layouts of WCF it specifies much higher caps?
I have some caps here where I could get 30uf as it asks for?

 

[Matador]

Ultimately the cap size depends on the input impedance you want to drive and what pole you want in the filter response. 1K will look like 25K to the output (with a 5:1), so 2.2u into 25K passes over 2Hz which seems like a good level for something intended as a bass preamp. Even a vintage 600ohm input looks like 15K which is ~5Hz which seems ok as well.

 

[Spencerleehorton]

Thank you Matador, I think I’m good now with this.

 

[Matador]

Also note the "ground lift" in post #43 is incorrect: it is mixing pin 1 shield with audio 0V, which is (potentially) injecting a pin 1 problem unnecessarily. Pin 1 should go directly to the chassis: full stop. The only reason to possibly lift this connection to the chassis would be if this would end up driving an unbalanced input (but then why even use a balanced output, given you already have an unbalanced output?).

Chassis can connect to audio 0V, in only one place, and is best done right at the input jack.