single ended silvertone clone attempt has bad background hum

[Helmholtz]

i never checked the power supply ripple. because i dont knownhownto use my oscilloscope to test over 300 volts...im not proficient with it yet....

No need to scope HV points.
After repairing the amp just scope the speaker output for the hum signal.
Hum frequency and waveshape can tell a lot.

if just the final 5uf preamp cap went bad, would i be able to eliminate that hum with the tone control which grounds the signal between the two stages of the preamp????

Most probably yes, as the input triode is the most sensitive to hum or ripple.

See if adding another 10µ/400V cap across existing filter caps lowers the hum.

[georage]

ok it will probably be a while before a get back to providing new info...i disconnected the power supply board and tested it by connecting the pt center tap to the capacitor ground and disconnecting all other grounds...with the 6x4 hooked up and dialed in the scope...it showed ripple free dc power on all caps.....
i might have discovered a ground loop on that power board as my main pcb board grounded to the power board, but also grounded though the pots at various points( will move the main board ground to the star ground).

other that that i'll start over will all your advice in mind.

my wire nut ground is solid, i trust it. i install wirenuts for a living, but i can solder the ground. dont wanna miss an obvious mistake.

im pretty sure i killed the cathode resistor with the soldering iron...

[georage]

one more thing that is challenging me is that the schematic states that the plate voltage on the 12ax7 should be 75 volts....however with the tremelo cut out the plate voltage is way high! i increased the resistor to get the voltage down to 250v but until the heaters warm up, the plates are seeing 300+ volts. im not sure how to deal with that as the 6v6 wants 320v and the 12ax7 wants 75v with one power supply.

[Helmholtz]

First of all, the value of the plate voltage has nothing to do with your hum problem.

Look at he schematic.
With the tremolo circuit in place R20 (100k) is shared by the plate currents of the input triode and the tremolo modulator tube.
So the voltage drop across R20 is caused by the sum of 2 plate currents.
With tremolo removed R20 drops less voltage, so the plate voltage of the input tube rises
That's not a bad thing at all, might even improve performance as 75V is very low for an input tube.

As said, I would make the junction of R20 and R5 another power supply node by adding a filter cap to ground here.
This will significantly lower any residual ripple for the input tube.

BTW, if you scoped your power supply without a load, there won't be any ripple because ripple is the consequence of a load current discharging the filter caps..

[georage]

Helmoltz! i did not realize that without a load, the power supply would not produce a ripple. thank you for pointing that out. i would have never figured that out not sure how i tested that, but it was probably under load....the amp is in a heap now...time to start over.

[sparkies]

Just because I didn't see it (nor I noticed anybody mentioned it) . Make sure C10 is not installed.