5f2 build problem

shay · 09-29-2009, 10:07 PM

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 · 09-29-2009, 10:46 PM

Does the switchable feedback have any effect on the waveforms?

shay · 09-30-2009, 07:53 AM

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

Enzo · 09-30-2009, 09:16 AM

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 · 09-30-2009, 09:11 PM

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 · 10-01-2009, 11:57 AM

Post a pic of the build, especially pot wiring.

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

shay · 10-05-2009, 09:21 PM

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 · 10-06-2009, 09:06 AM

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 · 10-06-2009, 10:44 AM

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 · 10-06-2009, 10:57 AM

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 · 10-06-2009, 12:26 PM

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

shay · 10-20-2009, 09:07 PM

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

09-29-2009, 10:07 PM	#1
shay Junior Member Join Date: Sep 2009 Posts: 14	5f2 build problem 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

09-29-2009, 10:46 PM	#2
loudthud Supporting Member Join Date: May 2006 Location: Texas USA Posts: 918	Does the switchable feedback have any effect on the waveforms? __________________ WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personel.

09-30-2009, 09:16 AM	#4
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 10,287	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. __________________ Education is what you're left with after you have forgotten what you have learned.

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09-30-2009, 07:53 AM	#3
shay Junior Member Join Date: Sep 2009 Posts: 14	No, except to do what i would expect it to do when i can see a clean signal

09-30-2009, 09:11 PM	#5
shay Junior Member Join Date: Sep 2009 Posts: 14	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

10-01-2009, 11:57 AM	#6
MWJB Old Timer Join Date: Jun 2006 Posts: 1,920	Post a pic of the build, especially pot wiring. What are your dc voltages for power tube & preamp tube?

10-05-2009, 09:21 PM	#7
shay Junior Member Join Date: Sep 2009 Posts: 14	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

10-06-2009, 09:06 AM	#8
MWJB Old Timer Join Date: Jun 2006 Posts: 1,920	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?

10-06-2009, 10:44 AM	#9
shay Junior Member Join Date: Sep 2009 Posts: 14	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??

10-06-2009, 10:57 AM	#10
MWJB Old Timer Join Date: Jun 2006 Posts: 1,920	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.

10-06-2009, 12:26 PM	#11
shay Junior Member Join Date: Sep 2009 Posts: 14	I will try splitting the grounds and a general tidy up and see what happens Cheers

10-20-2009, 09:07 PM	#12
shay Junior Member Join Date: Sep 2009 Posts: 14	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

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