The Amp Garage

Here's a few more clips:

No nfb, no fizz cap: 82pF fizz cap, still no nfb: With fizz cap and nfb reconnected: I still hear buzzy distortion - particular on lower notes, and the raspy/gritty decay.

Here's acouple of zoom-ins on those tops.
Not sure which function shows it most correctly - "High-res" or "average":

High-res: Average: Will try reconnecting the nfb (wouldn't that bring back the pi distorting before the output tubes?)
and the fizz cap

ok, first I tried reversing the OT primaries - but that made the amp oscillate, so I put them back where they were. Then I disconnected the 47K feedback resistor. It did help with the waveforms, showing that the pi now distorts after the power tubes. However, the gritty raspy decay on notes are stil...

Actually the ppimv is/was all the way up for these measurements, so that shouldn't be the culprit.
Anyways, I'll see if I can't get around to messing with the output plate leads, and the nfb tail when I get home tonight.

I think it shows up at the same time

Here's a few more shots, turning up the gain.
Light blue is across OT secondary, dark blue and purple is power tube grids.

ok, with Rombergs instructions, I got some scope snapshots made. Yellow trace is signal generator Blue is across the OT secondary. First at clean, gain at noon: OT out - gain at noon - clean.png Second is gain at about 1 o clock: OT out - gain at 1 o clock.png Third is same setting - pink trace is f...

ok, small update: When looking at trying to put a 33k grid stopper on the 3rd stage, I started wondering why the 220k mentioned earlier seemed to actually be right there as a grid stopper.... oooh... I had put the 330k to ground "before" the 220k, instead of from the grid to ground. Fixed that - sta...

Thanks a lot for your continued input! :-) I think the cables are ok. They are about a year old - planet waves. About crossover distortion: Not really thinking a lot - I don't know too well how blocking and crossover distortion sounds, since most of what I find is other people's description by word....

I would stop all drive stages up to the PI with a 33k on each and see if that totally fixes it. Input stage included.. There's already a 33k on the input. The thirds stage has a 220k/330k voltage divider right in front of it - I assume that one doesn't need a stopper? That leaves only the second st...

I have to confess, I'm a little worried about loosing the "chime" I hear in Simons demo, but I'll try the stoppers and see.

I just put together a spreadsheet with my voltages, and the voltages that others have reported, in the package documents I recieved in here.
Here's a link for my spreadsheet:
https://www.dropbox.com/s/xeysvdeitkjr6 ... .xlsx?dl=0

Not sure I understand what that is - can you elaborate?

ok, tried putting a 10k stopper on the PI. (between the 1m, 220K/330K junction and the grid pin.)
Couldn't really tell the difference - the harsh raspy fade-out is still there.

Here's a quick noodling - hoping it shows what I mean. https://www.dropbox.com/s/wuq3tc6wu806tov/sound%20clip.wav?dl=0 Amp settings: Gain, treble, mid, presence: 1 o'clock Bass: 11 o'clock HiCut: between 2-3 o'clock. Biasing: 32,2 & 37,8 mA @ about 485V on the plates It's a strat type guitar, neck+m...

Gridstoppers on the powertubes are 820R, as in the schematic. Currently I'm using SED 6l6. I've tried various other tubes (JJel34, JJel34II, JJkt77, SED EL34, EH 6ca7), and all have the same problem, with the 6l6's being the least "offensive".
I'll see if I can make a clip tonight.