5f2 build problem

[shay]

Hi all
I have built a 5f2 clone thats pretty much stock ,except for a switchable feedback loop, single input and star-grounding.
I have used triode electronics champ transformer bundle
The problem is that I am getting an ugly distortion and some crazy waveforms on my scope at any volume except at full or near it when the sound clears up and looks ok on my scope.
I've checked the wiring and layout and everything seems fine according to the fender circuit diagram.
Any suggestions are welcome

[loudthud]

Does the switchable feedback have any effect on the waveforms?

[shay]

No, except to do what i would expect it to do when i can see a clean signal

[Enzo]

There should be a 220k from pin 5 of the power tube to ground. is it present, and is it the correct value? A good idea is to measure resistance right from pin 5 to ground - that tests the resistor and the wiring. Likewise, is the cathode resistor proper and near value. When operating, what DC voltage is present on the cathode of the power tube - pin 8? close to schematic? And is ther any DC voltage on pin 5? Should not be any.

[shay]

There is a 220k resistor at pin 5 on the power tube and its ok and going to ground there is no dc volts on pin five and both the resistor and the voltage at pin 8 match the circuit

[MWJB]

Post a pic of the build, especially pot wiring.

What are your dc voltages for power tube & preamp tube?

[shay]

Sorry about the delay in replying,
here are the DC voltages on the valves, do they sound about right?

12a7x
pin 1 219v
pin 2 zero
pin 3 1.5v
pin 6 221v
pin 7 zero
pin 8 1.6v

6v6
pin 3 358v
pin 4 378v
pin 5 zero
pin 8 23v

I need to tidy up what was once a tidy build but after days of ripping apart does not look good anymore so as soon as thats done I'll send pictures.
I notice that with nothing plugged in and the volume up i'm getting hissing and some hi freq whistling , with the volume down everything is quiet

[MWJB]

voltages look good, no indicator of anything untoward there. Describe your gounding scheme, how have you grounded the components, e.g. where to and were they soldered (if so to what) or bolted?

What kind of chassis did you use?

[shay]

The Chassis and project are being shoehorned into one of those epiphone 5w
valve combos.I have run all grounds back to a bolt in the chassis and ensured there is good contact between the pots and the chassis and their cases are grounded. I was starting to think that the o/p transformer may be interfering with the pre amp as it is very close , Is this a runner??

[MWJB]

It's a good idea to have the preamp grounds separated from the power amp grounds, e.g. 12AX7 cathodes & filter cap can go to the input jack ground reference.

Main & screen filter caps, 6V6 cathode resistor & grid load resistor can go to a PT bolt ground.

The EVJ has the power tube & preamp tube situated very close to each other, it's possible that your layout subsequently has an issue...I think we really need some pics to move forward.

[shay]

I will try splitting the grounds and a general tidy up and see what happens
Cheers

[shay]

Success at last!!! , I changed the grounding layout as suggested by MWJB but this didn't improve matters so out came the scope . I had high frequency oscillations on the output with no input and the volume anywhere but full on,
So I went back to my layout/ lead dress one more time and there it was, I'd run the primary wires of the o/p transformer way too close to 100k resistor going to volume pot. Changed the run and I have one cool sounding little tweed clone.
Thanks again for all your help