Calculating plate load resistance & voltage for load line use

[Tonewood]

I would like to draw a load line for the first stage of V2 of the attached Sears amp. I'm not sure what voltage and resistance values to use.
Maybe (220k +330k) || 100k = R , V = 235 ?

Any idea why R2 is in this circuit? Also, I notice the V3 grid circuit is 10x higher than the 0.5M max value listed in the data sheets. (treble needs to be turned up to sound good) What problems might this cause?
Thanks!

[uneumann]

I would like to draw a load line for the first stage of V2 of the attached Sears amp. I'm not sure what voltage and resistance values to use.
Maybe (220k +330k) || 100k = R , V = 235 ?

Any idea why R2 is in this circuit? Also, I notice the V3 grid circuit is 10x higher than the 0.5M max value listed in the data sheets. (treble needs to be turned up to sound good) What problems might this cause?
Thanks!

OK - I'll bite - interesting circuit for a small amp. If you ignore R2 everything is pretty straightforward. First stage has a 100K dc load and a 100k//220k ac load. Put R3 back in and it provide NFB for the second stage AND adds to the load on the first stage. R2 has the be driven by the first stage and it's tied to the second stage output. Since the second stage has a gain of 16x (from the drawing), R2 is effectively 330k/16 =~20k. That swamps the 100k and 220k loads - you can ignore them. That's why the first stage only has a gain of 7 (again from the drawing).

You could also infer the first stage effective load since the fist stage is unbypassed. In that case, the stage gain is ~ the ratio of plate load to anode load. If the stage gain is 7, Plate load must be ~7x cathode load (or 7 x 1.5k) or ~21k.

I'll leave the tone control issues aside.

[J M Fahey]

Agree and add:
Unusual circuit in such an amp, but guess they had way too much gain for what they wanted (as in: 1 triode not enough; 2 triodes too much) so they went for 2 triodes and padded gain down for some NFB.

Can't think any other reason for that.

[Chuck H]

Agree and add:
Unusual circuit in such an amp, but guess they had way too much gain for what they wanted (as in: 1 triode not enough; 2 triodes too much) so they went for 2 triodes and padded gain down for some NFB.

Can't think any other reason for that.

In other words... Snip out R2 for more gain

I agree about the grid load for V3. I don't think changing R19 to a 500k pot (and a corresponding change of C11 to something like .022uf) would hurt a thing.

You could also replace R16 with a 250k pot and feed the V2 grid from the wiper (maybe add a "bright cap too). That would give you a more proper "volume" control. Which you might want if you increase gain.

Sorry, I'm no good with load lines.

[Tonewood]

Thanks everyone! All useful replies.
It's not my amp but if I have my way I will Snip R2, move the volume pot & change the tone ckt.
Dang, just noticed the ps canned caps are way close to (at) the limits with our area high line voltage. Maybe I will up those and lower the R22 1k dropper that's ahead of the OT for a bit more voltage/headroom.
Thanks again.