1-Tube Reverb question

[Lectroid]

I starting digging into the voltages on the 12DW7 1-tube reverb on my 18 watt amp. The reverb works well, considering it has one tube, and a short tank.  But my understanding of reverb drivers is weak and I'm hoping for a sanity check.

The driver tube's cathode voltage measure at 11.4 volts at idle. The driver circuit looks like a basic triode gain stage, but a load line using the DCR of 1090 ohms would be nearly vertical; I don't understand how that would work, either.  So I tried Ohm's Law. 

Assume: B-node is 316V, V2a plate voltage is 308V, the cathode resistor is 1500R, and using the DCR as the plate load value.

That gives a voltage drop of 8 volts.  (?)

    ( 8V / 1090 ) = .0071A,  7.34 mA, of plate current. 

Then expected current across the cathode resistor becomes:

    (1500R * .00734A)  =  11.0V

If that's right, the calculated value of 11.0V is fairly close to the measured 11.4V, and I can assume the reverb is fine?  Should I reduce / increase the cathode voltage by adjusting the cathode resistor?

What would be the parameters to draw a load line for this triode in this circuit? 

[Merlin]

You are correct in everything, except the load for AC signals is not simply the DCR but the reflected primary impedance. There was a thread about this recently.
https://el34world.com/Forum/index.php?topic=31734.msg349501#msg349501
Anyway it sounds like your reverb is working normally.

[Lectroid]

Thanks for the reality check.  And the readings. Never built a single-ended amp but I have more understanding now.

[stratomaster]

The cutoff for the filter into the driver triode is pretty low, about 160 Hz.  Do you find the reverb tone dark and the dwell a bit odd on the lower notes? 

I personally find limiting the reverb signal bandwidth to ~350Hz - 3.5kHz allows me to be a bit more radical with the effect without mudding up the dry signal. I accomplish this by shrinking the coupling cap into the driver triode, and a bypass cap of about 470pF up to 680pF on the recovery triode plate resistor.   This can clean up some hash in the tone too. You can also shrink the coupler to the reverb pot as it's currently full bandwidth, and leave the coupler into the driver relatively large to help move the springs.

Making some tasteful choices in frequency filtering could help overcome the shortcomings of the one tube reverb. 

[Lectroid]

Stratocaster,

Thank you.  Sorry I missed this last week.

That was short but full of ideas.  Especially the overall lesson to consider an entire circuit path as a tone-shaping unit, not just one filter at a time.  It's a skill I need to learn.   Thanks again.