Filament buss question

I don't what we did, maybe the 100k resistors, maybe I've just listened so much anything sounds good. The sweep on the depth pot still seems lacking, to me. But 100% is pretty good, as these clips will show. At 50% it's still quite faint, to my ear. I'll record that next and let you guys decide.

One without reverb:


And one with reverb:

 

Thanks, Keith. That's my '71 Super with the magical CTS alnicos . I'm on the vibrato channel, but verb is on zero, and trem is disabled (no footswitch).

 

I'll measure the grids again, before rolling tubes.

I'll also attempt to measure C30 and R45 (cathode pair).

I'll take stock of my low-value half-watt resistors, for potential tweaking. Might not have much on hand.

That C26 .0047 cap... The one I pulled was closer to 4.2nf, and the replacement (orange drop 715p 600v, not Mallory) was closer to 4.7nf.


Let me know what you think, when you get a chance to listen. In the meantime, I'll roll some tubes through V4 - I have a bunch.

Yeah! Really interesting, though I'm a bit past my limit of comprehension.

I was reading the patent application last night, and there are enough differences in Leo's original treatment of what we call V4 that I'm confused how much different the 6G12 (and ours) is from the patent.

The hi/lo filters are handled differently, with splitting into hi and wide band, then reducing the latter to bass only with negative feedback. Huh?

But then he takes GREAT care to describe that cathode arrangement. In particular:

"The high-value cathode resistor 67 [in his schematic] has been found to be extremely important in creating greater tremolo (differential amplification) action in the triodes, so that tremolo-frequency waves need only have relatively small amplitudes."

He goes on to describe how the high value of the resistor causes (if I understand correctly) the cathode voltage to fluctuate with the grid voltage - ever-changing due to the tremolo frequencies applied to the grid. He's saying this special feature enhances the whole warbly thing, I think. Is he saying that this is unique because the input signal and cathode work together to continually rebias each triode, 180 degrees apart? Or am I totally lost (again)...

Thing is, he recommends a 15k cathode resistor. Interesting...

Here's the document once more, worth a link.

 

Listen to my clips back-to-back with @Snfoilhat's latest, after he fixed the missing capacitor in his build. Now his is the five-triode, not four, but they share the same output section, where the guitar signal comes in.

I hear more *apparent* pitch modulation in his clip, than I do in mine. In other words, his sounds better, to me. What do y'all think?

 

Here are a couple of quick recordings at 50% depth.

 

Sad to see your empty room. We need a new video once you're settled again.

Clip sounded great! I'm making headway, but not quite there yet.

 

Rolled a bunch of tubes, they all sound the same to me. Nothing more chewy at 50%, for instance.

Before doing that, I clocked the grids and cathode.

Order: V4a, V4b, and Cathode.

Depth 100%:

No signal: 1.48 vpp, 2.04 vpp, and 3.56 max
100 hz: 1.48, 2.36, and 3.60
5k hz: 1.7, 2.08, and 3.56


Depth 50%:

No signal: 360 mvpp, 120 mvpp, and 3.2 vmax
100 hz: 290 mv, 620 mv, and 2.54 vmax
5k hz: 464 mv, 392 mv, and 708 mv max



Also, the cathode resistor and cap measure 4.71 k, and 2.242 uf.


I'll be online tomorrow (Tues), but won't available for testing until evening. Infusion day.

I have a few smallish resistors on hand, but no trimpot. I'm going to order a selection tomorrow morning, and get them shipping.

 

Thanks! Yours is really sounding good!

Good to know about your pot sweep. While it would be nice to have a full useable sweep, I really just need it to go a bit deeper, I think. As you say, it's most 'harmonic' above 8.

I see that Doug Hoffman also sells the pot. He actually calls it the ReVibe pot. Mine from Weber is nearly 11M, and it's just not made very well. I was thinking of getting a replacement, since they could be difficult to source.

So, higher max value means more depth, right? If the output triodes' cathode is so sensitive, as @clintj feels, it seems the depth would be another moving part in that equation. Wonder what adding a 2M resistor to that pot would sound like?

 

But that's not what I found. I posted earlier about this. Both this and the 3mra speed pot are only reversed taper, not overall. So resistance is highest on 10, but they roll back 'slow', retaining well over half their value at the 50% mark.