motor boating on a twin

[Curranproducer]

I just ordered a new set of F&T's for this fucker, I need it to work, it is killing me!!!

[Curranproducer]

there are the 1k5's going to pin 5 on each tube and the 470R going to pin4

[Curranproducer]

those are the original CC resistors as well

[Stevem]

Look closely at those 1.5Ks as many times they are cracked and or arced over on the bottom and you can not even see it, in fact I if the amp will be a player and not a piece of art I just replace those flame prone carbon types with a metal film type!

[Curranproducer]

I am jumping into that tonight, I bought 1watt 1k5's and 5watt 470R's to clean this mess up, I hope I cna get it right sooner rather than later. I also popped a 47pf silver mica across the plates (pins 1, and 6) of the PI to no avail

[Firestorm]

Both channels rules out reverb issues (most times). Is the PI input cap 001 or 01? Are the PI plate resistors 82K/100K or 47K/47K? Actually, in either case, I wonder if this might not be an unusual blocking distortion symptom. Maybe try taking the coupling caps from the PI down:. 047 or even . 022.

[Curranproducer]

re-did the resistors sets 1K5's, and the 470R with no success. I switched the resistors in the PI to the 100k/82k version for the blackface mods. All the caps have been changed to new orange drops in the PI I will check the values again so I will post later today

[Stevem]

Small caps like you added to the output tubes are at the other end of the frequency spectrum from your motor boating issue , so I would remove them!

One change you can try / do is to move the ground wire from the power supply filter node that feeds the output tube screens (pin 4 ) from the brass strip at the lower front of the amp over to the main red/ yellow wire that is the B+ ground over by the PT, as that is where it should have been in the first place!
You will likely need to extend and or replace that ground wire to go that distance!

[Curranproducer]

I didn't add any caps to the power tubes, that 47pf silver mica is on the phase inverter plates(pin1, and 6) I redid the resistors on the power section sockets

[Curranproducer]

I recapped the power section with the F&T's with no change I will now go and and reduce the PI coupling caps!

here is a link of pic's for the amp, maybe someone can see what the hell I am doing wrong

https://www.dropbox.com/sh/l80qkpfho5jk ... miY7a?dl=0

[Stevem]

Do not reduce those caps as you will just be treating the symptom and not the root cause of the issue and the amp will still be liable to not sound right even though it does not motor boat any more!

Did you move that ground wire yet that posted about, if not you should !

[Curranproducer]

I am reviewing the layout and the schematic and do not understand where this ground wire is on the amp? I will be fine with moving it but I need to find it 1st. is it coming off of the 100uf caps and going to a brass plate on the front of the amp or is it coming off of the power tube sockets?

[Stevem]

It's the ground wire that is on the power supply filter ( second filter node ) that is after the choke, this filter is 20 uf if it's value is still stock.

[Curranproducer]

Ok moved the ground wire from both of the filter nodes to the B+ spot. No change the orange drop going into pin 2 of the PI is a .001 the three orange drops after that are .1's from pin 7 and too pin 1 and 6

[Stevem]

If you lift the feedback wire coming off the speaker Jack does the issue get worse, better, or no change?