Input tube

[Mats]

Im looking at the input of an 5E3.
12AY7 tube, 820 Ohm cathode and 100k for each plate.
What would happen if there is common cathode, lets say 1k- 1k5 Ohm and dissimilar plate
resistors, lets say 100k and 220k ?
For Tone ?
Or is it a bad thing to hook up this way ?
Followed by the same volume and tone for 5E3.

I have looked at tube in parallel, as anode mixer with dissimilar cathode circuits.

[tubenit]

OK, let's say a 1.5k  cathode resistor that is shared. 

That would be like having a 100k plate resistor and a 3k cathode resistor.  Somewhat cooler and less gain.

And then having a 220k plate resistor and a 3k cathode resistor.  Somewhat warmer and more gain.

With respect, Tubenit

[Mats]

Hi
and thanks for answer.
So then it will be like test and listen.
Different values for cathode and the two plates.
Once again thanks from a, for the moment, sunny Sweden.

[tubenit]

Here is simply an idea to consider.

Would be like 2.4k cathode & 100k plate  ............. &  2.4k & 180k.   Might be able to dial in some nice clean to mean tones.

You could dial the clean (2.4k/100k) up or down ............ and dial the mean (2.4k/180k) up or down.

We could call this the "Deluxe Clean to Mean" mod.  

With respect, Tubenit

* On the idea with the bright switch,  I probably would add a 4.7M resistor to ground between the .02 off the plate and the SPDT.

[Mats]

Hi
Thanks for answer.
I notice that one Vol-pot is wired, "the other way around" to a 5E3.
I think I have seen this wiring somewhere else, perhaps it was at Wattkins.
In this schematic here, one is wired like 5E3 and the other like a voltage divider to next stage.
Is there any special purpose ?

[tubeswell]

I notice that one Vol-pot is wired, "the other way around" to a 5E3.
I think I have seen this wiring somewhere else, perhaps it was at Wattkins.
In this schematic here, one is wired like 5E3 and the other like a voltage divider to next stage.
Is there any special purpose ?

Its just the way they're drawn in the schematics. Both vol pots and the tone pot are wired the same.

[tubeswell]

As to what happens load-line-wise (and assuming a HT voltage of 280V at the 5E3 V1 supply node), the following charts give you an idea (the 'readings' are ballpark, but that doesn't really matter):

1) with 100k plate resistor and a shared 820R cathode resistor, each triode looks like its seeing 100k plate load and ~1k5 cathode resistor (more or less), so you get a pretty much centre-biased load line a reasonable amount of harmonic (non-linear) distortion on the plate. The overall voltage gain, if fully bypassed, is about 55 hence:





2) with the same 100k plate load and a shared 1k5 cathode resistor, each triode looks like its seeing 100k plate load and 3k cathode resistor, so the bias is colder and the operating point slides down the load line towards where the grid curves get more bunched up, and the amount of harmonic (non-linear) distortion decreases for small signals, but increases for larger signals. The overall voltage gain, if fully bypassed, is still about 55 hence:





3) with a 220k plate load and a shared 820R cathode resistor, each triode looks like its seeing 220k plate load and 1k5 cathode resistor, so the bias is warmish and the operating point slides up the load line so that +1V swing on the grid will put you at the 0V grid curve, and the stage will go into grid-current-limit clipping with just 2Vp-p input signal, but there is not too much harmonic (non-linear) distortion. The overall voltage gain, if fully bypassed, is about 68 hence:





4) with a 220k plate load and a shared 1k5 cathode resistor, each triode looks like its seeing 220k plate load and 3k cathode resistor, so the bias is cooler than '3' above, and the operating point slides back down the load line so that it can take a bigger signal on the grid without clipping, but there is slightly less harmonic (non-linear) distortion than '3' above for small input signals. The overall voltage gain, if fully bypassed, is about 68 hence.

[HotBluePlates]

Im looking at the input of an 5E3. 12AY7 tube ... What would happen if there is common cathode, lets say 1k- 1k5 Ohm and dissimilar plate
resistors, lets say 100k and 220k ? ...

... you get a pretty much centre-biased load line a reasonable amount of harmonic (non-linear) distortion on the plate. ...

You should see these examples assume a 1v peak signal, which is ~5-10 times what you'll have at the input tube. So the distortion at the input stage should be low no matter what values you choose (unless you really, really mis-bias the tube to saturation or cutoff, but then you have trouble getting any clean tones).

That said, you should still see how the large plate load setups still give more voltage amplification, and are therefore more likely to push the 2nd gain stage into distortion.