Hey guys,
So i managed to fix all my problems except 1 (I got preamp Heaters at 10.6vdc stable, is that ok?).
1. Had low distortion (was a bad anode resistor, was shorting for whatever weird reason)
2. had no channel switching (jack was bad)
3. Had hardly any volume (was a shielded wire ground gone bad in the fx loop send)
amp was working fine, I came back the next day to play and I got very very low volume with some hum and fizziness inside the sound.
I Plug in the fx return, no sound at all, even with master full up, i checked the entire poweramp section (resistors/non electrolytic capacitors)
checked all preamp tubes and power amp tubes in a different amp, working fine.
so it's not tubes.
I do get very low volume with humming sound when i plug into input, but no sound in fx loop return, does that make sense ?
the last thing i did to the amp was replacing the shielded wire in the fx loop with a different shielded wire, checked for shortages and there are none, could it be that the jack is bad for whatever reason ?
how do i continue troublshooting ? really lost now
no sound from fx loop return
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Stevem
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Re: no sound from fx loop return
What amp are we taking about here?
It sounds like you still have a issue in the power supply as if the preamp tubes are powered with DC it needs to be at least 12 volts, not 10.6!
It sounds like you still have a issue in the power supply as if the preamp tubes are powered with DC it needs to be at least 12 volts, not 10.6!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
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Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: no sound from fx loop return
this is the fx loop
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Re: no sound from fx loop return
Ang3lus,
Let's get this working. I'll suggest a few quick trouble shooting tips that you can perform in less time than it took to type this. Generally, if the volume is faint, with hum there is a grid open somewhere - you are either hearing bleed through the power supply or capacitive coupling. Here is how I would suggest trouble shooting this fx loop.
First we will focus on the recovery stage of the fx loop, pins 6, 7 and 8.
1) Turn the master up after the fx loop.
2) Is there V+ available at the plate load resistor?
3) Is there ground at the cathode resistor
4) Is there a voltage drop across the plate load?
5) Is there a voltage "on top" of the cathode resistor?
6) Is the tube in a normal operating condition.
7) If you touch the grid with the probe of the DMM is there a pop or "disturbance"?
8 ) Is there a signal available at the grid if a signal is injected earlier in the preamp? What if a signal is injected into the fx return jack?
IF the above works as expected move to the next step IF not, fix the problems here first. Check all wiring, voltages again - including heater voltages. Also move closer to the power amp, touch the PI input with a DMM probe - is there a pop?
IF working:
9) Plug a known working patch cord into both fx jacks. What is the resistance from patch cord tip to ground? 70K?
10) Move to the first half of the tube, pins 1,2,and 3.
11) Repeat steps 2 through 8 on pins 1,2,and 3. Is there voltage, ground, is the tube in an operating condition, signal? Disturbance test?
IF both sides of the tube are in an operating condition and the patch cord measures approx 70k to ground and disturbance pops happen when the grid 2 is touched with a DMM, remove the patch cord and try the DMM disturbance on pin 2 again. Does it pop? IF not, then it is your jacks. IF it works, keep moving towards the input, stage by stage as detailed above.
Remember,
Check Voltage, ground, voltage drops, is the tube operating, is there signal... etc etc etc.
Just a guess, most likely when you added the shielded cable, either the shield shorted to the center conductor, the center conductor is broke, or the jacks / wiring is bad. I once had a solid core wire break inside the insulation and was intermittent - took a while to sus that one out.
I don't want to simplify things, but tube amps are simple IF taken stage by stage. Using a DMM alone (disturbance tests) or a scope, DMM and signal generator should take less than 5 minutes to find the problem.
Good luck.
Let's get this working. I'll suggest a few quick trouble shooting tips that you can perform in less time than it took to type this. Generally, if the volume is faint, with hum there is a grid open somewhere - you are either hearing bleed through the power supply or capacitive coupling. Here is how I would suggest trouble shooting this fx loop.
First we will focus on the recovery stage of the fx loop, pins 6, 7 and 8.
1) Turn the master up after the fx loop.
2) Is there V+ available at the plate load resistor?
3) Is there ground at the cathode resistor
4) Is there a voltage drop across the plate load?
5) Is there a voltage "on top" of the cathode resistor?
6) Is the tube in a normal operating condition.
7) If you touch the grid with the probe of the DMM is there a pop or "disturbance"?
8 ) Is there a signal available at the grid if a signal is injected earlier in the preamp? What if a signal is injected into the fx return jack?
IF the above works as expected move to the next step IF not, fix the problems here first. Check all wiring, voltages again - including heater voltages. Also move closer to the power amp, touch the PI input with a DMM probe - is there a pop?
IF working:
9) Plug a known working patch cord into both fx jacks. What is the resistance from patch cord tip to ground? 70K?
10) Move to the first half of the tube, pins 1,2,and 3.
11) Repeat steps 2 through 8 on pins 1,2,and 3. Is there voltage, ground, is the tube in an operating condition, signal? Disturbance test?
IF both sides of the tube are in an operating condition and the patch cord measures approx 70k to ground and disturbance pops happen when the grid 2 is touched with a DMM, remove the patch cord and try the DMM disturbance on pin 2 again. Does it pop? IF not, then it is your jacks. IF it works, keep moving towards the input, stage by stage as detailed above.
Remember,
Check Voltage, ground, voltage drops, is the tube operating, is there signal... etc etc etc.
Just a guess, most likely when you added the shielded cable, either the shield shorted to the center conductor, the center conductor is broke, or the jacks / wiring is bad. I once had a solid core wire break inside the insulation and was intermittent - took a while to sus that one out.
I don't want to simplify things, but tube amps are simple IF taken stage by stage. Using a DMM alone (disturbance tests) or a scope, DMM and signal generator should take less than 5 minutes to find the problem.
Good luck.
Re: no sound from fx loop return
WOW!!!!!!!
thanks for the awesome advice
i did most of what suggested, though you have some more notes that are really awesome for troublseshooting, i believe this post should be pinned for all people trying to trouble shoot and are running out of ideas.
I do have a question about the fx loop, I did the patch cord thing, and i did measure 70k, but I also measure it without the patch cord, does that mean the jack is shorting ?
also, no sound in the fx loop return and no popping when i touch any of the tubes, turned full up.
thanks for the awesome advice
i did most of what suggested, though you have some more notes that are really awesome for troublseshooting, i believe this post should be pinned for all people trying to trouble shoot and are running out of ideas.
I do have a question about the fx loop, I did the patch cord thing, and i did measure 70k, but I also measure it without the patch cord, does that mean the jack is shorting ?
also, no sound in the fx loop return and no popping when i touch any of the tubes, turned full up.
Re: no sound from fx loop return
Safety First, as above, some of the tests below are with power applied and in an operating condition, others must be with the amp off. Please be safe and very careful when probing around the power and preamp tubes and the power rail.
Regarding the fx loop resistance, 70k measured without the patch cord shows that the jacks are wired correctly. From the fx scheme, there is 100k on the send to ground and 56k and 180k on the return side. These are in parallel and equal approximately 70k to ground.
So, IF the fx loop tube is in operating condition - current is passing through, voltage drops across the resistors, the grids are connected etc - and when injecting a signal into the return jack there is no sound your troubles are most likely after the fx loop recovery stage.
Also check the grid to ground resistance, of the fx tube pin 7 the resistance should be approximately 47k, grid to ground (the same resistors as above are now "configured" differently as our test point has moved.
Moving forward, I would now approach it this way, start from the very end
Power amplifier stage.
Check speaker cable and jack output wiring.
Check the power amp:
Now we go into the same routine voltages, ground, signal
Measure power tubes:
Bias voltage - the most important voltage in the amp
Check Heater voltage
Measure Plate voltage
Measure Screen Voltage
Make sure there is ground at the power tube cathodes
Is the tube in an operational condition / state? You do have 1 ohm "bias" resistors right?
Is there a signal?
Faint Scratchy sound or pop when doing a disturbance test?
Is there continuity between the PI coupling caps and PA grids, grid leaks in place, no shorts to ground, no unintentional Post PI MV wiring errors?
Move to the PI
Components in place? Coupling caps? Pull on the wires to check for loose connections, broken conductor, bad solder joints? Check all shielded cables for a short to the conductor.
Same thing, Voltage, Ground, Signal. Like the post above is there a voltage drop across the plate resistors? Across the cathode resistor? Is the tube in an operating state? Perform the disturbance test, the pop should be a little louder. What happens if you inject a signal to the PI input cap?
Is there continuity back to the FX "master" volume. Does the resistance value on the signal line look appropriate? Does the resistance from the PI input cap (fx loop side) to ground change as the master is rotated?
And so on and so on until you find the problem or get to the input....
One additional note, from the power supply scheme, it looks as there are a number of relays - make sure that the signal is not being grounded there or a relay connection is "open". Your DMM is your friend.
Remember, voltage, ground, is the tube in operating condition, signal....
I hope that you can figure it out, it will take more time powering the amp on and off between tests than to find the problem. Use the tools that you have. Inject a signal at various points and grids, find out what works and what doesn't - injecting a signal or using the disturbance test is a very fast method - all of the grids can be tested in seconds.
Also, take a marker and follow the schematic coloring in the components and wires as you trouble shoot.
Good luck, be safe, take things in small steps, mark up the scheme and take notes. Remember once again, Voltage, Ground, operating condition, Signal (which includes continuity of wiring and not having shorts or "opens").
Regarding the fx loop resistance, 70k measured without the patch cord shows that the jacks are wired correctly. From the fx scheme, there is 100k on the send to ground and 56k and 180k on the return side. These are in parallel and equal approximately 70k to ground.
So, IF the fx loop tube is in operating condition - current is passing through, voltage drops across the resistors, the grids are connected etc - and when injecting a signal into the return jack there is no sound your troubles are most likely after the fx loop recovery stage.
Also check the grid to ground resistance, of the fx tube pin 7 the resistance should be approximately 47k, grid to ground (the same resistors as above are now "configured" differently as our test point has moved.
Moving forward, I would now approach it this way, start from the very end
Power amplifier stage.
Check speaker cable and jack output wiring.
Check the power amp:
Now we go into the same routine voltages, ground, signal
Measure power tubes:
Bias voltage - the most important voltage in the amp
Check Heater voltage
Measure Plate voltage
Measure Screen Voltage
Make sure there is ground at the power tube cathodes
Is the tube in an operational condition / state? You do have 1 ohm "bias" resistors right?
Is there a signal?
Faint Scratchy sound or pop when doing a disturbance test?
Is there continuity between the PI coupling caps and PA grids, grid leaks in place, no shorts to ground, no unintentional Post PI MV wiring errors?
Move to the PI
Components in place? Coupling caps? Pull on the wires to check for loose connections, broken conductor, bad solder joints? Check all shielded cables for a short to the conductor.
Same thing, Voltage, Ground, Signal. Like the post above is there a voltage drop across the plate resistors? Across the cathode resistor? Is the tube in an operating state? Perform the disturbance test, the pop should be a little louder. What happens if you inject a signal to the PI input cap?
Is there continuity back to the FX "master" volume. Does the resistance value on the signal line look appropriate? Does the resistance from the PI input cap (fx loop side) to ground change as the master is rotated?
And so on and so on until you find the problem or get to the input....
One additional note, from the power supply scheme, it looks as there are a number of relays - make sure that the signal is not being grounded there or a relay connection is "open". Your DMM is your friend.
Remember, voltage, ground, is the tube in operating condition, signal....
I hope that you can figure it out, it will take more time powering the amp on and off between tests than to find the problem. Use the tools that you have. Inject a signal at various points and grids, find out what works and what doesn't - injecting a signal or using the disturbance test is a very fast method - all of the grids can be tested in seconds.
Also, take a marker and follow the schematic coloring in the components and wires as you trouble shoot.
Good luck, be safe, take things in small steps, mark up the scheme and take notes. Remember once again, Voltage, Ground, operating condition, Signal (which includes continuity of wiring and not having shorts or "opens").
Last edited by John_P_WI on Sun Mar 08, 2015 12:23 am, edited 1 time in total.
Re: no sound from fx loop return
thanks for all the truly great advice!!!
i hope i will have some time thursday to check it all out
i hope i will have some time thursday to check it all out
Re: no sound from fx loop return
Good luck, Ang. Hope that you and others can gain a few tricks, that us older guys have picked up over the years through different disciplines, and help you learn how to troubleshoot problems in a few minutes.
Thanks for the comment Bob
John
Thanks for the comment Bob
John