i hope you where running a resistor as a dummy load because you'd be hurting your output transformer otherwise!
Turk 182,
I did not use a dummy load however all of the pots were at their lowest position and there was no input attached to the amp. How do I determine if I have damaged the transformer?
I did connect the speakers to the amp to see if I could hear anything but all was quiet except for a slight scratchy sound when I flipped the switch for standby on and off. Not I still do not have any input yet. My son had his guitar cables stolen so I'm a little in the dark until he replaces them, should be early this week.
Should I be able to hear anything without a guitar attached? Is there something or somewhere I should check? How are the speaker wires supposed to be attached to the amp? I plugged the speaker cord into the 16-ohm output, attached the spade connectors to the positive side of the speakers and attached the short wire to each negative side. Does it matter?
Thanks again for your help.
Len
I did not use a dummy load however all of the pots were at their lowest position and there was no input attached to the amp. How do I determine if I have damaged the transformer?
I did connect the speakers to the amp to see if I could hear anything but all was quiet except for a slight scratchy sound when I flipped the switch for standby on and off. Not I still do not have any input yet. My son had his guitar cables stolen so I'm a little in the dark until he replaces them, should be early this week.
Should I be able to hear anything without a guitar attached? Is there something or somewhere I should check? How are the speaker wires supposed to be attached to the amp? I plugged the speaker cord into the 16-ohm output, attached the spade connectors to the positive side of the speakers and attached the short wire to each negative side. Does it matter?
Thanks again for your help.
Len
are you doing this on the "lamp limiter" or are you on "regular"AC?
if your on regular ac, the speakers are hooked up, it's on,the output tube plates aren't glowing orange, it's not popping fuses or breakers,there's no magic white smoke rising up! so far so good!
as far as your speaker wiring it does matter what goes where you don't want to hook them up out of phase! you did say you checked the speakers? without an input and all levels down you would have to get close to the speaker to see if you can detect any type of residual hum or background blow or hiss.
if your on regular ac, the speakers are hooked up, it's on,the output tube plates aren't glowing orange, it's not popping fuses or breakers,there's no magic white smoke rising up! so far so good!
as far as your speaker wiring it does matter what goes where you don't want to hook them up out of phase! you did say you checked the speakers? without an input and all levels down you would have to get close to the speaker to see if you can detect any type of residual hum or background blow or hiss.
what did Jack Darr call it the "circuit disturbance test" or "finger on the input jack"(only done after checking for any hazardous potentials at the input jack)
This was on "regular" AC, as you said, no drama, etc.
When I had the speakers attached I did play with the pots. There was no sound from the speakers. I have them, still attached to the speaker board, sitting on the bench next to the amp chassis, so within inches of my ear. I only heard the slight sounds as the switch was thrown.
As for the speakers what is considered "in-phase" for a guitar amp? I connected the outputs from the transformer (through the cord/plug/jack) to the positive points on the speakers and connected the short jumper to the negative tabs. I'm used to stereo speakers where each one has a connector output to connect to each speaker/box.
Thank you for your help and patience.
Len
When I had the speakers attached I did play with the pots. There was no sound from the speakers. I have them, still attached to the speaker board, sitting on the bench next to the amp chassis, so within inches of my ear. I only heard the slight sounds as the switch was thrown.
As for the speakers what is considered "in-phase" for a guitar amp? I connected the outputs from the transformer (through the cord/plug/jack) to the positive points on the speakers and connected the short jumper to the negative tabs. I'm used to stereo speakers where each one has a connector output to connect to each speaker/box.
Thank you for your help and patience.
Len
in phase simply mean that they're traveling in the same direction (if there not you'll loose bass response due to cancellation)
a quick test with a 1.5V battery will confirm that (try testing one speaker first; noting the polarity of the battery with respect to the driver terminals. a quick touch will make the speaker move either in or out depending on how you've hooked things up) in your case you can either wire your speakers in parallel or series either way this battery test will confirm that they're "in phase".
this applies to stereo speakers too wire either channel out of "polarity"or "phase" with the other you will notice if not turn off the stereo and open the scotch!
i guess my post about the "circuit disturbance test" warrants further explanation.
a quick test with a 1.5V battery will confirm that (try testing one speaker first; noting the polarity of the battery with respect to the driver terminals. a quick touch will make the speaker move either in or out depending on how you've hooked things up) in your case you can either wire your speakers in parallel or series either way this battery test will confirm that they're "in phase".
this applies to stereo speakers too wire either channel out of "polarity"or "phase" with the other you will notice if not turn off the stereo and open the scotch!
i guess my post about the "circuit disturbance test" warrants further explanation.
Yes, but unfortunately none good. I have been especially busy lately. My wife took a spill and hurt her back, nothing critical but she did slightly herniate a disk. She is on the mend so I'm hoping to get back to trouble shooting again this weekend.
I was tracing voltages and I'm getting slightly different readings than called out on the schematic. My -14 volt rail seems fine everywhere I check it but the -27 volt rail I'm only getting a little over 24-volts. I'm reading the voltage at R38 to ground. If I'm reading the schematic correctly this corresponds to the Vcc- pin on the RC4558, opamp, U1. I'm just not sure what is forcing the voltage down. Any suggestions?
Thank you very much for your continued interest in my problem.
Len
I was tracing voltages and I'm getting slightly different readings than called out on the schematic. My -14 volt rail seems fine everywhere I check it but the -27 volt rail I'm only getting a little over 24-volts. I'm reading the voltage at R38 to ground. If I'm reading the schematic correctly this corresponds to the Vcc- pin on the RC4558, opamp, U1. I'm just not sure what is forcing the voltage down. Any suggestions?
Thank you very much for your continued interest in my problem.
Len
Forcing? remember, this is a guitar amp, not a NASA space probe. Voltages are approximate. I sure would not concern myself over 24v versus 27v there. And as long as the 14v is more or less half of the supply, it will be OK too.
measure your -27 at the pair of 22 ohm resistors in the supply. But really, just close is fine. I see no trouble in your numbers.
Think of "-27" and "-14" more as names than test point voltages. Just as in the high voltage, they just name them B+ and B++ and no voltages given. If we don;t need to specify B+ voltages, we SURELY don't need to be precise for the reverb IC.
measure your -27 at the pair of 22 ohm resistors in the supply. But really, just close is fine. I see no trouble in your numbers.
Think of "-27" and "-14" more as names than test point voltages. Just as in the high voltage, they just name them B+ and B++ and no voltages given. If we don;t need to specify B+ voltages, we SURELY don't need to be precise for the reverb IC.
I'm rather limited in my testing abilities at the moment. I only have a DMM and now a dim bulb tester. I did try using the guitar to feed the amp and trace the signal with it powered off, but it was very difficult to strum, probe, and look at the meter at the same time. Not to mention at between 100-500 mV, I wasn't sure exactly of what I was reading. I was able to follow it to the first tube in the pre-amp section, but it is very hard to get the probes past the tubes while it is all installed in the chassis.
Will I be able to read the signal from the guitar through the tubes without the amp being powered? Can I use some kind of signal generator/probe to follow it?
Thanks again for your help.
Len
Will I be able to read the signal from the guitar through the tubes without the amp being powered? Can I use some kind of signal generator/probe to follow it?
Thanks again for your help.
Len
Hmmm. OK, you know the voltages in the amp can KILL YOU, so please be careful.
No, you cannot trace signal through the amp with the power off.
I only use the guitar when I am finished and want to verify it sounds GOOD. Otherwise I use a test signal, because as you said, it is hard to strum and work at the same time. A signal generator is fine, but not necessary. I have all manner of good signal generating equipment, but in general I just use music. I have a cheap stereo receiver on th bench just for the music. I run a cable from its output in the back (RECORD OUT it says) and tuned to a music station, my FM becomes a test signal. Other than when the DJ is talking, the music is a reasonably steady signal, and full range, so perfect as a test tone.
I think what turk182 meant was this: does sound come out the speaker when a signal in applied to the input?
For signal tracing, I use a scope, but lacking that, a AC voltmeter will follow a signal pretty well. A tube amp should have a substantial signal voltage after the first stage. If you are ever unsure if the voltage you are reading is signal, just turn the input off and see if it goes away.
A very useful thing that used to be standard equipment on an audio bench was the Signal Tracer. Google that and see all manner of examples. ALl it is is a amplifier with a probe at the input. You can probe something and hear what is there. I(t includes a DC blocking cap at the input. When you google it, some examples will include diodes. Those are for radio ffrequency listening. You do not need the diode version. REally, this is only maybe one step more complex than your bulb tester. So pretty simple.
No, you cannot trace signal through the amp with the power off.
I only use the guitar when I am finished and want to verify it sounds GOOD. Otherwise I use a test signal, because as you said, it is hard to strum and work at the same time. A signal generator is fine, but not necessary. I have all manner of good signal generating equipment, but in general I just use music. I have a cheap stereo receiver on th bench just for the music. I run a cable from its output in the back (RECORD OUT it says) and tuned to a music station, my FM becomes a test signal. Other than when the DJ is talking, the music is a reasonably steady signal, and full range, so perfect as a test tone.
I think what turk182 meant was this: does sound come out the speaker when a signal in applied to the input?
For signal tracing, I use a scope, but lacking that, a AC voltmeter will follow a signal pretty well. A tube amp should have a substantial signal voltage after the first stage. If you are ever unsure if the voltage you are reading is signal, just turn the input off and see if it goes away.
A very useful thing that used to be standard equipment on an audio bench was the Signal Tracer. Google that and see all manner of examples. ALl it is is a amplifier with a probe at the input. You can probe something and hear what is there. I(t includes a DC blocking cap at the input. When you google it, some examples will include diodes. Those are for radio ffrequency listening. You do not need the diode version. REally, this is only maybe one step more complex than your bulb tester. So pretty simple.
if your still accumulating test stuff it's time to get an assortment of alligator clips and j hooks to make connections to your device under test safe, probing randomly and trying to hold too many probes and strum a guitar is a recipe for disaster (in my neophyte days i destroyed or damaged probe tips with a quick slip or unintentional short to an adjacent pin)
even without a signal source you can still check that an amp is passing sound/signal by touching the tip of the jack cord without contacting ground if the amp is working you will/should hear a loud buzz honk from your speakers(the Jack Darr "circuit disturbance test")
so after checking that all connections i.e. board connector, wiring to jacks ( front and rear) and controls(pots) are at levels that should produce output what do you have, sound or not?
even without a signal source you can still check that an amp is passing sound/signal by touching the tip of the jack cord without contacting ground if the amp is working you will/should hear a loud buzz honk from your speakers(the Jack Darr "circuit disturbance test")
so after checking that all connections i.e. board connector, wiring to jacks ( front and rear) and controls(pots) are at levels that should produce output what do you have, sound or not?
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Thank you both for your input.
In answer to both; no, there is no sound coming from the speakers when a signal is applied to the input of the amp. I even tried the circuit disturbance test and still had no luck.
I have already invested in a set of 10-leads with alligator clips at each as well as a set of Cat. III probes and J-hooks. It still took more coordination than I could muster.
I took Enzo's advise and used the earphone output from an old boom-box and feed it into the input and tried to follow the signal. I was able to detect the signal, I think (I didn't note Enzo's advice to remove the signal to determine if it is the signal or not.), as far as the R1/C1 juncture. To get farther I will need to remove the board from the chassis. I'll be doing that tomorrow night.
As an aside, how do I determine if the ribbon cable connecting the 2-tube sections (J12-J47) are properly connected? I see no marking on the schematic or board as to which side the black stripe should be on each board. Since I fell prey to a misplaced jumper by someone previous to me, I just want to make sure this is correct as well. Any suggestions?
Thanks again for your patience and help.
Len
In answer to both; no, there is no sound coming from the speakers when a signal is applied to the input of the amp. I even tried the circuit disturbance test and still had no luck.
I have already invested in a set of 10-leads with alligator clips at each as well as a set of Cat. III probes and J-hooks. It still took more coordination than I could muster.
I took Enzo's advise and used the earphone output from an old boom-box and feed it into the input and tried to follow the signal. I was able to detect the signal, I think (I didn't note Enzo's advice to remove the signal to determine if it is the signal or not.), as far as the R1/C1 juncture. To get farther I will need to remove the board from the chassis. I'll be doing that tomorrow night.
As an aside, how do I determine if the ribbon cable connecting the 2-tube sections (J12-J47) are properly connected? I see no marking on the schematic or board as to which side the black stripe should be on each board. Since I fell prey to a misplaced jumper by someone previous to me, I just want to make sure this is correct as well. Any suggestions?
Thanks again for your patience and help.
Len
the ribbons are usually flat and should have no twists,the black strip normally corresponds to the lowest pin number as long as the cables have no twists(as in run flat from board to board)things should be ok.
a signal tracer or scope would make your life easier but it's not undoable!
rather than trace all the way through the preamp i'd try to inject signal at the phase inverter (V3B pin 7)to see if the output stage is working (being careful of the signal level it can get loud fast)once you know that's ok i'd continue tracing backwards through the preamp if you still have a problem
a signal tracer or scope would make your life easier but it's not undoable!
rather than trace all the way through the preamp i'd try to inject signal at the phase inverter (V3B pin 7)to see if the output stage is working (being careful of the signal level it can get loud fast)once you know that's ok i'd continue tracing backwards through the preamp if you still have a problem
Update - My efforts at tracing with my multimeter failed miserably, I was not able to accurately follow what I thought was the signal, so I broke down and have ordered an oscilloscope, a Rigol 1102E. It should be here later this week or early the next.
Until then the amp will sit.
Len
Until then the amp will sit.
Len
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