Congratulations
As of:
Like jumping with a parachute and having it open 10 feet above ground
Yes, it will "limit" your speed somewhat ... from 250 Mph to , say, 230 Mph
To put some numbers into it: crudely, it can be said that a bulb limits power available from mains to a sizable fraction of its rated power.
Pure guessing, but say it limits to 60% just to pick a number.
So a 40W to 100W bulb will let enough power through for troubleshooting , but stop *big* damage if you have a problem, while a 250W one will let as much through as the amp needs when going full blast, directly connected ... in practice not limiting.
Best it can do, though, is to protect your home wiring, but not the amp.
As of:
it was already answered: a too large bulb will allow so much current through that it's not doing its job, in practical terms "it's not limiting".
Like jumping with a parachute and having it open 10 feet above ground
Yes, it will "limit" your speed somewhat ... from 250 Mph to , say, 230 Mph
To put some numbers into it: crudely, it can be said that a bulb limits power available from mains to a sizable fraction of its rated power.
Pure guessing, but say it limits to 60% just to pick a number.
So a 40W to 100W bulb will let enough power through for troubleshooting , but stop *big* damage if you have a problem, while a 250W one will let as much through as the amp needs when going full blast, directly connected ... in practice not limiting.
Best it can do, though, is to protect your home wiring, but not the amp.
Hoi Victoriaguy,
Quote:
The original complaint was buzzing/humming?
But the first bunch of diagnoses seemed to focus on "DC on the outputs", which confused me.
Well I encounter daily similar complaints or descriptions of the amp symptoms.
It's hard for a non technical person or a beginner to exactly describe the problem.
I to have problems from time to time to express myself in decent English.
What I think or call it is therefore not what an English native speaker thinks or calls it.
If every body would like to speak and write Dutch, it would make my life a lot easier...
Any way, we still have the greatest bear in the world (not the size but the taste)
Cheers
Quote:
The original complaint was buzzing/humming?
But the first bunch of diagnoses seemed to focus on "DC on the outputs", which confused me.
Well I encounter daily similar complaints or descriptions of the amp symptoms.
It's hard for a non technical person or a beginner to exactly describe the problem.
I to have problems from time to time to express myself in decent English.
What I think or call it is therefore not what an English native speaker thinks or calls it.
If every body would like to speak and write Dutch, it would make my life a lot easier...
Any way, we still have the greatest bear in the world (not the size but the taste)
Cheers
Ahh, I happens more then you think. Even after years of repairing amps I sometimes overlook the reverb circuit or the speaker. Then I have to remove the chassis, the knobs, the nuts, etc, etc...
So welcome in the club.
A quick test is the following:
The reverb can seems to be ok.
1. Check with an ohm meter the cables going to and from the reverb can with the can disconnected.
2. Then switch the amp on and touch the tip of the red rca connector and set the reverb pot at 10. You should here a decent buzz. Another way is to wiggle the can with the red rca connector connected to the can. You should here the typical reverb spring noise.
3. Connect the tip of the black rca connector to a small speaker or through a potentiometer (say 10K and at mid position) and so to the tip of the red rca connector.
You should here your guitar getting through.
Now let's see what you find. (1, 2, 3)
So welcome in the club.
A quick test is the following:
The reverb can seems to be ok.
1. Check with an ohm meter the cables going to and from the reverb can with the can disconnected.
2. Then switch the amp on and touch the tip of the red rca connector and set the reverb pot at 10. You should here a decent buzz. Another way is to wiggle the can with the red rca connector connected to the can. You should here the typical reverb spring noise.
3. Connect the tip of the black rca connector to a small speaker or through a potentiometer (say 10K and at mid position) and so to the tip of the red rca connector.
You should here your guitar getting through.
Now let's see what you find. (1, 2, 3)
Results of performing tests on your list, Tarzan:
1. Check with an ohm meter the cables going to and from the reverb can with the can disconnected. They are fine.
2. Then switch the amp on and touch the tip of the red rca connector and set the reverb pot at 10. You should here a decent buzz. Another way is to wiggle the can with the red rca connector connected to the can. You should here the typical reverb spring noise. Nothing happens when I touch the tip of the red RCA connector (after disconnecting it from the "out" jack of the reverb pan. I also don't hear any spring sounds if I drop the pan. The reverb control was set at 10 for this test.
3. Connect the tip of the black rca connector to a small speaker or through a potentiometer (say 10K and at mid position) and so to the tip of the red rca connector.
You should here your guitar getting through. Can you explain a little more what this test looks like? I don't have a spare speaker or 10k pot.
1. Check with an ohm meter the cables going to and from the reverb can with the can disconnected. They are fine.
2. Then switch the amp on and touch the tip of the red rca connector and set the reverb pot at 10. You should here a decent buzz. Another way is to wiggle the can with the red rca connector connected to the can. You should here the typical reverb spring noise. Nothing happens when I touch the tip of the red RCA connector (after disconnecting it from the "out" jack of the reverb pan. I also don't hear any spring sounds if I drop the pan. The reverb control was set at 10 for this test.
3. Connect the tip of the black rca connector to a small speaker or through a potentiometer (say 10K and at mid position) and so to the tip of the red rca connector.
You should here your guitar getting through. Can you explain a little more what this test looks like? I don't have a spare speaker or 10k pot.
I tested the RCA cable by removing all 4 plugs from the circuit and using a multimeter to test continuity between the two tips and two jacks. Cleaned and jumped FX send/return jacks with a patch cable. I did hear a buzz when I plugged in the patch cable to the FX send jack, but still no buzz when touching the red RCA plug.
Took measurements at each side of R20 and R21 (the 180 ohm 3 watt resistors) on the preamp board. Voltages were measured with respect to chassis ground.
- PSU -VE: -34 and -24, measured at each side of R20
- PSU +VE: +33 and +17 VDC, measured at each side of R21
Should that +17 be closer to +24?
Took measurements at each side of R20 and R21 (the 180 ohm 3 watt resistors) on the preamp board. Voltages were measured with respect to chassis ground.
- PSU -VE: -34 and -24, measured at each side of R20
- PSU +VE: +33 and +17 VDC, measured at each side of R21
Should that +17 be closer to +24?
Cheeto333,
It seems that the receive side of your reverb circuit (IC1D) isn't working wel because the transducers on the pan measured ok.
But it can also be a power supply problem.
There fore you have to measure the supply voltages on the IC1, pin 4 and 7. - and + voltages towards ground. these should be very close to + and - 12V.
But I believe they are ok as the rest of the preamp seems to work and the IC's are fed from the same source.
So I suspect a broken IC1.
Although it's not proven yet.
Oh, can you do another quick test?
Touch pin 12 of IC1 with your finger (via a piece of wire) while you do not touch the chassis or whatever part of your amp. You will introduce hum and that should be audible through your amp. - Set reverb level at max.
If there is no hum, we will go through anther test, but first this step.
Slowly slowly we get there...
It seems that the receive side of your reverb circuit (IC1D) isn't working wel because the transducers on the pan measured ok.
But it can also be a power supply problem.
There fore you have to measure the supply voltages on the IC1, pin 4 and 7. - and + voltages towards ground. these should be very close to + and - 12V.
But I believe they are ok as the rest of the preamp seems to work and the IC's are fed from the same source.
So I suspect a broken IC1.
Although it's not proven yet.
Oh, can you do another quick test?
Touch pin 12 of IC1 with your finger (via a piece of wire) while you do not touch the chassis or whatever part of your amp. You will introduce hum and that should be audible through your amp. - Set reverb level at max.
If there is no hum, we will go through anther test, but first this step.
Slowly slowly we get there...
Ah were are getting closer.
So this proves the opamp IC1 is "working". Probably for a 100%.
You say that the cable to the red phono jack is ok.
What is between the cable and pin 12 of IC1:
C15 that's open. Try to insert some hum with the tip of a screwdriver at R25 where it comes together with C 14 and 15 the same way as explained in post 56.
C13 that's shorted. Measure if there is indeed a short to ground or a low resistance.
C14 that's open. A short on C13 will influence this test.
If there is no short on C13 touching the tip of the red rca connector would make some buzz audible. But that's already done in post #52.
I neither of these tests gives a result, then a broken track or bad solder joint on C14 and/or C15. Back to partially post #32. Inspect the pcb foil and redo the solder joints of said caps.
If still no buz (after mouting everything back in to the chasis) replace C15 and C14.
It has to work now.
Unless... There is a problem at the solder joints and pcb track of PH2.
Check that one to before replacing the caps.
So this proves the opamp IC1 is "working". Probably for a 100%.
You say that the cable to the red phono jack is ok.
What is between the cable and pin 12 of IC1:
C15 that's open. Try to insert some hum with the tip of a screwdriver at R25 where it comes together with C 14 and 15 the same way as explained in post 56.
C13 that's shorted. Measure if there is indeed a short to ground or a low resistance.
C14 that's open. A short on C13 will influence this test.
If there is no short on C13 touching the tip of the red rca connector would make some buzz audible. But that's already done in post #52.
I neither of these tests gives a result, then a broken track or bad solder joint on C14 and/or C15. Back to partially post #32. Inspect the pcb foil and redo the solder joints of said caps.
If still no buz (after mouting everything back in to the chasis) replace C15 and C14.
It has to work now.
Unless... There is a problem at the solder joints and pcb track of PH2.
Check that one to before replacing the caps.
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