Help troubleshoot first build. More info was added (updated again)

[hesamadman]

Hey guys.

Heres what happened.

2204 50 watt
Triode Electronics Layout
Hammond Transformers


Finished the build. Plugged it in. HEard slight pop. Thought maybe it wasd the speaker since the power and standby was both flipped in. Anyway. I checked plate voltages. When I was checking this my lead slipped and arced something. Was a small arc and a small pop. I proceeded to bias amp. adjusted bias to 38MV. Tubes were still lighting up after arc. Bias was set. Thought I would plug in guitar and try it. Speaker was humming like it should so I thought it was going to work. Guitar plugged into one input I got a little volume. When it was plugged into the other input I didnt get any volume.

Output tube voltages-
1-
2- 2.7 vAC I know this should be 1.15. not sure of the tolerance and my meter may be bad.)
3- 442vDC
4- 434 vDC
5- -30vDC
6- 439 vDC
7- 2.9vAC
8- 38 mV DC

Bias pot-
located on opposite side of chassis.








***************** I went through and checked all resistors. I ordered a capacitor meter also but not here yet. The image Im uploading is the layout. The THREE components with a green rectangle over them are the ones that are not reading correct. I have a 1m on the high gain thats bad. That might be why im not getting input there. I also have a 470k on the low gain that is only reading 320k. And a 100k thats bad.

Is this a result of the arc? Or maybe were they bad? or maybe did I burn them up during soldering? Are all possibilities?

[hesamadman]

Weird.

The 100k resistor will not read 100k while its installed. It only reads about 9k. But when I removed it from the board and tested...it was fine. I replaced it anyway.

[sluckey]

Weird.

The 100k resistor will not read 100k while its installed. It only reads about 9k. But when I removed it from the board and tested...it was fine. I replaced it anyway.

Not weird at all. I bet the new resistor reads just like the old one when in circuit. There is stuff that parallels that 100K when in circuit. The only way to accurately measure a resistor in circuit is to analyze the circuit to see if anything parallels the resistor. If so, you must disconnect one end of the resistor to make the measurement.

[hesamadman]

Weird.

The 100k resistor will not read 100k while its installed. It only reads about 9k. But when I removed it from the board and tested...it was fine. I replaced it anyway.

Not weird at all. I bet the new resistor reads just like the old one when in circuit. There is stuff that parallels that 100K when in circuit. The only way to accurately measure a resistor in circuit is to analyze the circuit to see if anything parallels the resistor. If so, you must disconnect one end of the resistor to make the measurement.
[/quote

MAKES PERFECT SENSE!! Thank you so much!!

[Ed_Chambley]

It would help a lot to get voltages of all your tubes, not just the power tubes.  Like this;
v1 pin 1-180vdc
pin 2-
pin 3-
4&5 Heaters
pin 6-
pin 7-
pin 8-
pin 9 heater

Do this with all of your tubes.  For instance if you were to have 20vdc on pin 1 of v3 or 45 volts in pin 6 of v3, then we can narrow down some problems.  For instance, if your signal prior to the Power tubes is lacking because of an incorrect resistor, this will tell where you need to check.

[hesamadman]

It would help a lot to get voltages of all your tubes, not just the power tubes.  Like this;
v1 pin 1-180vdc
pin 2-
pin 3-
4&5 Heaters
pin 6-
pin 7-
pin 8-
pin 9 heater

Do this with all of your tubes.  For instance if you were to have 20vdc on pin 1 of v3 or 45 volts in pin 6 of v3, then we can narrow down some problems.  For instance, if your signal prior to the Power tubes is lacking because of an incorrect resistor, this will tell where you need to check.

Can I check these voltages by pulling the tube and putting my lead in the top of tube socket? My hands are so shakey its hard to touch the lead inside the chassis.

[sluckey]

The tubes must be in the sockets for the voltage readings to be meaningful. Most problems with new builds will be a wiring error or incorrect value component. Compare your layout and schematic to the actual amp.

[hesamadman]

It would help a lot to get voltages of all your tubes, not just the power tubes.  Like this;
v1 pin 1-180vdc
pin 2-
pin 3-
4&5 Heaters
pin 6-
pin 7-
pin 8-
pin 9 heater

Do this with all of your tubes.  For instance if you were to have 20vdc on pin 1 of v3 or 45 volts in pin 6 of v3, then we can narrow down some problems.  For instance, if your signal prior to the Power tubes is lacking because of an incorrect resistor, this will tell where you need to check.

1st preamp tube-

pin 1- 260 vDC
pin 2-
pin 3-
pin 4 and 5- 2.7 vAC
pin 6- 220vDC
pin 7-
pin 8-
pin 9 around 2.7 ACROSS BOTH pin 9 AND pin 4/5 I GET ABOUT 5.9 vAC

2nd preamp tube-

pin 1- 170 vDC when my lead touches this I hear a noise in the amp.
pin 2-
pin 3- around 2-3 vDC
pin 4 and 5- 2.7 vAC
pin 6- 319vDC
pin 7-
pin 8-
pin 9 around 2.7 ACROSS BOTH pin 9 AND pin 4/5 I GET ABOUT 5.9 vAC

3rd preamp tube-

pin 1- 234 vDC when my lead touches this I hear a noise in the amp.
pin 2-
pin 3-
pin 4 and 5- 2.7 vAC
pin 6- 220 vDC
pin 7-
pin 8-
pin 9 around 2.7 ACROSS BOTH pin 9 AND pin 4/5 I GET ABOUT 5.9 vAC

 

[sluckey]

Need voltages for pins 1,2,3,6,7,8 for all little tubes.

[hesamadman]

Need voltages for pins 1,2,3,6,7,8 for all little tubes.

should they all be DC except the heaters?

[hesamadman]

Need voltages for pins 1,2,3,6,7,8 for all little tubes.

guessing third preamp tube isnt getting what it needs?

1st preamp tube-

pin 1- 260 vDC
pin 2- ~0
pin 3- 2.9
pin 4 and 5- 2.7 vAC
pin 6- 220vDC
pin 7- ~0
pin 8- 2.04
pin 9 around 2.7 ACROSS BOTH pin 9 AND pin 4/5 I GET ABOUT 5.9 vAC

2nd preamp tube-

pin 1- 170 vDC when my lead touches this I hear a noise in the amp.
pin 2- ~0
pin 3- 1.6
pin 4 and 5- 2.7 vAC
pin 6- 319vDC
pin 7- 170
pin 8- 180
pin 9 around 2.7 ACROSS BOTH pin 9 AND pin 4/5 I GET ABOUT 5.9 vAC

3rd preamp tube-

pin 1- 234 vDC when my lead touches this I hear a noise in the amp.
pin 2- 12 is this low?
pin 3- 41
pin 4 and 5- 2.7 vAC
pin 6- 220 vDC
pin 7- 13
pin 8- 12
pin 9 around 2.7 ACROSS BOTH pin 9 AND pin 4/5 I GET ABOUT 5.9 vAC

[SILVERGUN]

Minimally,,,,pins 3+8 on preamp tube #3 (not actually a preamp tube,,, it's your phase inverter) are a shared cathode connection, and should be the same reading, unless there is a wiring error....
Pins 2,3,7,8 on that same tube should all normally be around 40 vdc....with 2 + 7 being approx 1v less than pins 3+8

when my lead touches this I hear a noise in the amp

I'm assuming you mean that you hear a sound out of your speakers..
that is normal and OK, and indicates that your signal is (at least partially) getting through to your speakers...
Keep the amp turned down so as not to damage your speakers...

If your meter probe ever arcs again, make sure you are not connected to read current on your meter (on a standard Fluke, make sure that you dont have one of your leads plugged into the red receptacle marked "A")

[hesamadman]

Minimally,,,,pins 3+8 on preamp tube #3 (not actually a preamp tube,,, it's your phase inverter) are a shared cathode connection, and should be the same reading, unless there is a wiring error....
Pins 2,3,7,8 on that same tube should all normally be around 40 vdc....with 2 + 7 being approx 1v less than pins 3+8

when my lead touches this I hear a noise in the amp

I'm assuming you mean that you hear a sound out of your speakers..
that is normal and OK, and indicates that your signal is (at least partially) getting through to your speakers...
Keep the amp turned down so as not to damage your speakers...

If your meter probe ever arcs again, make sure you are not connected to read current on your meter (on a standard Fluke, make sure that you dont have one of your leads plugged into the red receptacle marked "A")

ok. well it seems as iff tube 3 has a problem. I am not getting no where near the voltages necessary in that 3rd preamp tube. Any suggestions why?

[SILVERGUN]

ok. well it seems as iff tube 3 has a problem. I am not getting no where near the voltages necessary in that 3rd preamp tube. Any suggestions why?

Trace your wiring to that tube and double check it against the layout....double check your resistor values
Does your wiring match the layout 100%?....i.e.- did you just jumper pins 3+8 on the tube socket? (if so, why the different voltage reading?)

Another very simple troubleshooting approach would involve you touching the meter to each "down-stream" signal point until you don't hear anything out of your speakers (just like you listed on pin #1 of tube #2 + #3.........what do you hear if you touch pins 1 or 6 on tube #1?).....that will help you narrow down the point where you are losing the signal

If you get a chance, give us a close up hi-res pic of your input jacks and volume control.....it doesn't appear that you have that vol. control wired to the ground buss as it is in the layout, and that is a very critical area,,,,,and,,cliff jacks have been known to get the best of some guys...

Good luck and stay with it,,,,we've all been through this 

[hesamadman]

ok. well it seems as iff tube 3 has a problem. I am not getting no where near the voltages necessary in that 3rd preamp tube. Any suggestions why?

Trace your wiring to that tube and double check it against the layout....double check your resistor values
Does your wiring match the layout 100%?....i.e.- did you just jumper pins 3+8 on the tube socket? (if so, why the different voltage reading?)

Another very simple troubleshooting approach would involve you touching the meter to each "down-stream" signal point until you don't hear anything out of your speakers (just like you listed on pin #1 of tube #2 + #3.........what do you hear if you touch pins 1 or 6 on tube #1?).....that will help you narrow down the point where you are losing the signal

If you get a chance, give us a close up hi-res pic of your input jacks and volume control.....it doesn't appear that you have that vol. control wired to the ground buss as it is in the layout, and that is a very critical area,,,,,and,,cliff jacks have been known to get the best of some guys...

Good luck and stay with it,,,,we've all been through this 

Ive gone over this amp over and over again since 9 am. Ive got nothing. I havent found a single mistake. The shielded wire from pin 2 to volume control is grounded to ground bus

[SILVERGUN]

Did you find any reason why you listed the voltages on pins #3+8 on tube #3 as two different voltages, when they should be connected, and reading the same voltage?

That could be where (some of) your problem is......

I'm about done for today, but we've gotten some good info out of this, and bigger fish will come along,,,,,and probably tell us why we're both wrong   

Do the probe testing I described earlier and find out where in the stream you are losing your signal......look at the schematic and follow the signal path, you WILL find it

[Willabe]

Can I check these voltages by pulling the tube and putting my lead in the top of tube socket? My hands are so shakey its hard to touch the lead inside the chassis.

Use the insulated (rubber boot) alligator spring clip that goes on the end of your meter prob. You should have gotten a pair of those when you bought your meter. If not then buy a pair. Rat shack has them as do all the major electronics supply houses.

Turn the amp off, clip the probe on the tube pin, turn the amp back on and take your reading. It will slow you down but so what? I use them a lot.

You're going to fix what's wrong, don't worry.

                  Brad      

[Ed_Chambley]

Hang in there.  I have been absolutely sure I had everything correct before, but it was not the case when I finally found the problem.  There is one true fact and I do not mean this harshly.

If it were all correct, it would be working correctly.

I can tell already you have some problems.  Hang in there and the guys will help get you going.  If Willabe says so, it is true.

[hesamadman]

Hang in there.  I have been absolutely sure I had everything correct before, but it was not the case when I finally found the problem.  There is one true fact and I do not mean this harshly.

If it were all correct, it would be working correctly.

I can tell already you have some problems.  Hang in there and the guys will help get you going.  If Willabe says so, it is true.

Look what I did now....


Well, I was testing voltages..... SAME DAMN THING. Same location too. Arced on power tube pin 6 and 7. This time it popped HT fuse. Replaced it. Fuse held.
NOW....no bias voltage. Was reading about this and the guys problem was his bad tubes. I bet my whole problem from the first arc was messing up first tube...and then second arc...same thing causing no bias voltage. Some of my other voltages were a lot higher after the second arc.

Any thoughts?

[hesamadman]

ive been working on this amp since 9 am....ha ha jesus

[Ed_Chambley]

Well, I was testing voltages..... SAME DAMN THING. Same location too. Arced on power tube pin 6 and 7. This time it popped HT fuse. Replaced it. Fuse held.
NOW....no bias voltage. Was reading about this and the guys problem was his bad tubes. I bet my whole problem from the first arc was messing up first tube...and then second arc...same thing causing no bias voltage. Some of my other voltages were a lot higher after the second arc.

Any thoughts?

[/quote]
Keep going.  Bad tubes normally will not cause the voltages you have checked.  I can see where you have some problems.  Take a break if you need to.  Keep in mind that this is part of the fun and great learning process.

Not sure how you could have lost your negative bias voltage.  Check it again coming off the leg of your adjustment pot.  See if you have DC there.

[hesamadman]

Literally cut every component off the board... removed all wiring. starting 100 percent over. Still say I ruined my tubes though

[eleventeen]

Ehhhh, that's not the good approach IMHO. What we humans do is to make an oversight error and continuously repeat it. "Starting over" does not in any way prevent you from making the same mistake again.

For example....it's very common for newbs to mentally number the pins on the tube sockets (or a connector) backwards. They realize their mistake...and proceed to rewire the thing EXACTLY THE SAME as it was the first time. Or...the classic one...is to be wiring a connector where you have to put the shell of the connector on BEFORE you make the connections. You put it together, then you realize you didn't put the shell on first. (I*&#^*$)((^_*( so you take it apart, cut off the end (and by the way, the more end preparation is needed, in other words you have to unravel a shield and get the wire lengths just right so that the jacketing ends up inside the shell...the more likely you are to repeat your error. AND YOU WIRE IT AGAIN and AGAIN forget to put the shell on before soldering. Hopefully you realize this before you make 11 connections, but only three.

There are several techniques, but what you want to do is to subdivide the circuit into power supply - preamp(s) - power amps. A listening amp (eg; signal tracer) could be useful testing out the preamps. For the power amp, you need to get the power supply (both B+ and bias) stable.

Another technique, not mutually exclusive, is to get a schematic and highlight-marker (the bright yellow or green type) out each wire as the connections are made. THIS IS DIFFERENT from doing the very same thing on a LAYOUT diagram. And it can be a little tricky because wiring to a layout diagram is A LOT different than wiring to a schematic! It is the most common thing I have seen on this forum to have a "layout" diagram have some sort of discrepancy from the schematic. Which one is right? I trust the schematic more because it is VERY EASY to mis-translate a schem into a parts-board dwg.

To do this, you MUST have the schematic on a clipboard or on some hard surface so that you don't have to drop everything (and thus lose your concentration) to drop your tool(s), pick up the piece of paper, pick up your magic-marker & make your mark. It has to be one-handed.

And while you're at it PUT A PIECE OF WIRE INSULATION ON YOUR DAMN METER PROBE, OK?

[Ed_Chambley]

Another technique, not mutually exclusive, is to get a schematic and highlight-marker (the bright yellow or green type) out each wire as the connections are made. THIS IS DIFFERENT from doing the very same thing on a LAYOUT diagram. And it can be a little tricky because wiring to a layout diagram is A LOT different than wiring to a schematic!

To do this, you MUST have the schematic on a clipboard or on some hard surface so that you don't have to drop everything (and thus lose your concentration) to drop your tool(s), pick up the piece of paper, pick up your magic-marker & make your mark. It has to be one-handed.

[/quote]
Great Comments.  Highlighting schematics (when I was coerced into doing it) has been the greatest troubleshooting thing I have learned.  Also, it is a grand way to understand the different components and what they do.  After doing it a couple of times, I began to understand how amps work.  Using a layout is fine, but it is like painting by numbers so not as much thought involved.

BUT, the biggest thing it has done for me after using them and taking notes is I can see a layout by looking at the schematic.  Lets face it, there are 2 ways.  Tubes up (my preference, but difficult on combos) or tubes down.  I dont build combos much at all.  To many benefits in using a head box.

[hesamadman]

Another technique, not mutually exclusive, is to get a schematic and highlight-marker (the bright yellow or green type) out each wire as the connections are made. THIS IS DIFFERENT from doing the very same thing on a LAYOUT diagram. And it can be a little tricky because wiring to a layout diagram is A LOT different than wiring to a schematic!

To do this, you MUST have the schematic on a clipboard or on some hard surface so that you don't have to drop everything (and thus lose your concentration) to drop your tool(s), pick up the piece of paper, pick up your magic-marker & make your mark. It has to be one-handed.

Great Comments.  Highlighting schematics (when I was coerced into doing it) has been the greatest troubleshooting thing I have learned.  Also, it is a grand way to understand the different components and what they do.  After doing it a couple of times, I began to understand how amps work.  Using a layout is fine, but it is like painting by numbers so not as much thought involved.

BUT, the biggest thing it has done for me after using them and taking notes is I can see a layout by looking at the schematic.  Lets face it, there are 2 ways.  Tubes up (my preference, but difficult on combos) or tubes down.  I dont build combos much at all.  To many benefits in using a head box.


[/quote]



There were just too many things I couldn't let be. The messy wiring. Messy soldering joints. My soldering iron broke in half so I was using a taped together iron that was floppy. Turret lugs were too small to fit some components. I bought crappy tube sockets. I just ordered a new soldering iron ($150 later. My old one costed 12) I'm re doing the entire board. Only things I didn't re order were the filter caps, pots, transformers, switches, and fuse holders. I mean, my bias pot was rigged up on the other side of the chassis. The ground bus looked like crap. I just said to hell with it. But I HAD to have damaged something when I touched pin 6 and 7 together on my el34 socket. I really believe it was the tube. I did it twice for god sake. Ha. Oh well. At least I didn't throw any of it across the room.

[Glennjeff]

You need to slow down inside your head. The shorting out and sparking with meter probes is a sure sign that your out of sync with the here and now of it all. HERE and NOW, one small, well calculated step at a time.

Take it really slow, rebuild it as a Zen Master would, plan 10 steps ahead as a Chess Master would.

Got the vibe.

Everyone here wants your success. If you need our help after the rebuild, try to take each piece of information the board members give slowly and thoroughly, do your best to get an intimate and organic understanding of what they are saying. It's foreplay man, don't rush it or you'll miss the best part.

All the best.

[hesamadman]

You need to slow down inside your head.

Take it really slow, rebuild it as a Zen Master would, plan 10 steps ahead as a Chess Master would.

Got the vibe.

Everyone here wants your success. If you need our help after the rebuild, try to take each piece of information the board members give slowly and thoroughly, do your best to get an intimate and organic understanding of what they are saying. It's foreplay man, don't rush it or you'll miss the best part.

All the best.

Thanks man. There were too many mistakes in the beginning. I want to fix them all. I would really like to understand more as to where the power amp starts and the pre amp starts. Any good reading that you can suggest?

[sluckey]

But I HAD to have damaged something when I touched pin 6 and 7 together on my el34 socket. I really believe it was the tube.

That's possible. You shorted the B+ screen supply to the filament. Does the EL34 filament still light up? With the tube out of the socket measure resistance between pins 2 and 7. How much?

[sluckey]

I would really like to understand more as to where the power amp starts and the pre amp starts.

The two 12AX7s on the right side of your layout make up the preamp. All the other tubes are the power amp.

[hesamadman]

But I HAD to have damaged something when I touched pin 6 and 7 together on my el34 socket. I really believe it was the tube.

That's possible. You shorted the B+ screen supply to the filament. Does the EL34 filament still light up? With the tube out of the socket measure resistance between pins 2 and 7. How much?

They did light up. And are at 1.7 ohms

[hesamadman]

I would really like to understand more as to where the power amp starts and the pre amp starts.

The two 12AX7s on the right side of your layout make up the preamp. All the other tubes are the power amp.

I understand the 12ax7s are the pre and the el34 are the ouput. I mean more along the lines on the circuit board I guess.

[eleventeen]

"Take it really slow, rebuild it as a Zen Master would, plan 10 steps ahead as a Chess Master would."

Dunno if newbs can do that. It takes a lot of builds before you can anticipate interferences with *any* degree of anything....and even then you get snarked sometimes.

"Everyone here wants your success. If you need our help after the rebuild, try to take each piece of information the board members give slowly and thoroughly, do your best to get an intimate and organic understanding of what they are saying. It's foreplay man, don't rush it or you'll miss the best part."

Heartily agree. The marking off of the schematic in and of itself imposes that discipline, IMHO. And that, therefore, is the item of process-control I believe is the best guarantee of success. The layout is a great thing to have but it gives you essentially ZERO understanding of the circuit. Of course the BIG trouble comes when you have a layout and populate your parts board from it. Check, check, check, cool, that's 35-40 things. Now, you go to the schematic for the connections to the tube sockets and THEN you find some weirdness. That pretty much forces you to stop and regroup.

[sluckey]

I understand the 12ax7s are the pre and the el34 are the ouput. I mean more along the lines on the circuit board I guess.

See pic...

[hesamadman]

I understand the 12ax7s are the pre and the el34 are the ouput. I mean more along the lines on the circuit board I guess.

See pic...

I had no idea the presence knob would have been part of power amp

[hesamadman]

I understand the 12ax7s are the pre and the el34 are the ouput. I mean more along the lines on the circuit board I guess.

See pic...

Oh damn....or that last 12ax7.

[sluckey]

This kind of stuff is much easier to see on a schematic. Learning to read a schematic requires some study and experience. Reading/Understanding a schematic leads to a better understanding of how a circuit works. And being able to relate a schematic to a layout or the actual amp is crucial to logical troubleshooting. It all takes time.

[eleventeen]

Nice dwg, Steve!

[hesamadman]

This kind of stuff is much easier to see on a schematic. Learning to read a schematic requires some study and experience. Reading/Understanding a schematic leads to a better understanding of how a circuit works. And being able to relate a schematic to a layout or the actual amp is crucial to logical troubleshooting. It all takes time.

happen to have a schematic of this amp?

Can you explain why the 12ax7 is part of power. I had no idea these were ever used there.

[alerich]

I just built a 2204 a few months ago. This is the schematic I worked from:

http://mhuss.com/MyJCM/JCM800_2204.gif

I crammed my amp into a small solid state combo chassis so it is all point to point (very little wiring) and I had to sorta lay it out as I went. I cannot over stress the importance of using a schematic and a highlighter. I think it's a crucial part of building an amp and/or troubleshooting that build.

Also. Check, check and recheck the value of components before you solder them in. My first "build" years ago was a rebuild of a Fender Vibro Champ that someone had hacked up. I replaced everything but the PT, OT, rectifier socket and chassis. I soldered in a 2K2 resistor at the grid of the 6V6. It is supposed to be 220K. I looked over that amp until I was cross eyed - probably a day and a half - before I found it. Check, check and recheck.

Just take your time and enjoy the build process. It's a tried and true design and it will work if wired properly.

[hesamadman]

I just built a 2204 a few months ago. This is the schematic I worked from:

http://mhuss.com/MyJCM/JCM800_2204.gif

I crammed my amp into a small solid state combo chassis so it is all point to point (very little wiring) and I had to sorta lay it out as I went. I cannot over stress the importance of using a schematic and a highlighter. I think it's a crucial part of building an amp and/or troubleshooting that build.

Also. Check, check and recheck the value of components before you solder them in. My first "build" years ago was a rebuild of a Fender Vibro Champ that someone had hacked up. I replaced everything but the PT, OT, rectifier socket and chassis. I soldered in a 2K2 resistor at the grid of the 6V6. It is supposed to be 220K. I looked over that amp until I was cross eyed - probably a day and a half - before I found it. Check, check and recheck.

Just take your time and enjoy the build process. It's a tried and true design and it will work if wired properly.

  thanks for the schematic and advice!

[alerich]

thanks for the schematic and advice!

You are very welcome. I did not compare that schematic I linked component for component to the layout diagram that you posted. They should be very close but sometimes one layout/schematic differs slightly from another. The differences (if any) are usually in the power supply in the form of slightly different cap values or dropping resistor values. The preamp and power amp portions should be the same. Just be cognizant of this. The schematic I posted was drawn from an actual Marshall JCM800 50 watt head so it's the real deal.

I suck at reading layout diagrams almost as much as I suck at reading tablature. My hats off to anyone who can build an amp that works the first time from a layout diagram.

[eleventeen]

And....have the schematic on a clipboard so you can just pick up the "marker" with one hand. Ideal would to have it on a music stand, at an angle, off to the side. It does little good to have it a: taped to the wall, or b: as a loose piece of paper on your bench. You want to be able to mark it up (and of course you are doing this in a spare copy) with ONE HAND, so you don't break your focus.

And...I will revise the suggestion to using a (red) colored pencil instead of a highlighter. Because you can erase a colored pencil but not a highlighter. And a highlighter with cap left off will dry out. What you want here is to have NO lines crossed out, and if you make a mistake with the highlighter (and you will) you can't effectively cross out your overshoot. You really want to get the feel of having your wiring progress sync with your drawing progress, all matching the schematic. That is very satisfying in an OCD way. And yet, it cannot be done in a solder-joint-by-solder-joint fashion, because some connections...go nowhere until the NEXT connection...and terminal strips do not show on schematics!

When you do this...you have to think, in advance, exactly how you are going to represent a wire that goes to a component. Do you....just color UP TO the component? Color HALF the component? Whatever way...you should be consistent.

And, another small conceptual challenge is, when you place a wire to a terminal strip, say, and have not yet connected it to anything else...what is that, in terms of your drawing? Is it a nothing or is it a something?

[Willabe]

This kind of stuff is much easier to see on a schematic. Learning to read a schematic requires some study and experience. Reading/Understanding a schematic leads to a better understanding of how a circuit works. And being able to relate a schematic to a layout or the actual amp is crucial to logical troubleshooting. It all takes time.

What Sluckey said here is very important and it does take time, but it's worth it. It will save you time and headaches in the long run.

Can you explain why the 12ax7 is part of power. I had no idea these were ever used there.

Look at the schematic. That tube is the phase inverter (PI) for the push/pull (PP) output power amp.

It splits the signal into 2 parts, the positive (+) phase and the negative (-) phase. The + phase goes to 1 power tube grid (push) through a coupling cap and the - phase goes to the other (pull) power tube grid again through a coupling cap. The coupling caps block the DC PI plate voltage from the output tubes grids so the DCV doesn't mess up the output tubes bias. It doesn't matter if the power tubes are grid or cathode bias, you still need them there. (Coupling caps are sometimes called blocking caps and are found anywhere in an amp where you need to block DCV from getting on the grid of a tube or any thing else, because a cap won't pass DCV only ACV.) The output transformer (OT) combines the 2 phases back together and sends the combined (AC) signal to the speakers.

The PI also drives the power tubes. The power tubes need to see enough signal fed to their grids so the output tubes plates can deliver enough AC signal voltage to the OT for the output wattage (power) the amp curcuit is designed for. The OT then transforms the power tubes high (AC signal) voltage/low (AC signal) current output signal into high current/low voltage signal to drive the speaker(s). It also blocks the high DC B+ voltage for the power tubes plates that's on the OT's primary from the OT's secondary that feeds/drives the speaker(s).  

I had no idea the presence knob would have been part of power amp.

Look at the schematic. What is the presence control wired too/fed from?

The presence control is wired to the OT secondary/speaker and is fed back to the PI. It's part of the negative feedback loop. It disables the negative feedback (-FB) as you turn the presence knob at the frequency roll off point set by the presence controls cap value. The -FB is shunted to ground through the presence cap.


              Brad      

[Willabe]

Here's the link to our host Doug's tube amp library of information. There's a ton of great reading in there.

(It can be found on the forums main page.)

 

http://www.el34world.com/schematics.htm



                   Brad      

[Willabe]

And forgot to say, that was not bad for a first build at all.  

Most guys build a little Champ single ended (SE) amp or a 5E3 tweed Deluxe for a 1st build. I went with the 5E3. The amp you picked for a first build was more complicated.

I still think you would have gottin that amp fixed.


              Brad    

[dude]

I've been where you're at a few times. You have the best advice here that you can get.

Do all the things mentioned, especially the insulated clips on your meter like Willabe  mentioned.

I did all my first few builds using a lay out, they were easier builds, like a 5E3. I got lucky the first time and the amp played great. I though, boy this is easy till the next build I had problems like you're having now. So this is normal.

If you don't understand the schematic and can't relate to the wiring by looking at the schematic, use the layout. And by all means double check every connection (and resistor value with your meter) just before before soldering, it will be slow but worth it. Once soldered make the mark on your layout and on the bd. a dot with a sharpie (non-permanent). This will help make sure your not making mistakes.

Another thing is the tendency to wire things backwards, like pots. So position your layout next to the build exactly the same and follow.

Now when your done and if the amp doesn't have the correct voltages don't start over. Go slow and recheck everything. It's hard to check the values of resistors wired in a circuit, so do what Sluckey recommended, measure the resistor before you solder it in place.

You could be having "cold solder joints or burning up components, don't leave the tip on a connection more than five seconds (hope you have the right tip). Heat both the lead and turret at the same time for about three/four seconds and then apply the solder to the lead not the tip, it should flow and be shinny when first done.

I still have some problems reading some schematics but I find I can now better repair or build an amp by the schematic than a layout.

Believe me you'll get it going, and remember you're dealing with high voltage that can hurt you so be careful.

Just the other day, I put a 7591 power tube NOS, in the 5Y3 rectifier socket and turned on the amp. I mixed the two tubes. After a few minutes trying to find out why I had no sound I saw the problem. But I fired a perfectly match NOS Westinghouse 7591.  We all still make mistakes, I'm still leaning.

Go slow, and keep posting.

al

 

[Ed_Chambley]

The big fish have arrived.  Think of this as learning.  If you build this amp with understanding of what you are doing, that will translate to many other designs.   Also, if down the road something happens, you will have a good idea of what is causing it.

[hesamadman]

Knowledge is the most important thing from this build.  

I appreciate it very much.

One thing in the schematic that I dont understand is the pots. They look just like regular resistors. But pots have three leads. So how do you know where things go?

EDIT: Oh i see it literally points to the center of the symbol for the center lead. :EDIT

[alerich]

Here's what happened.
Finished the build. Plugged it in. Heard slight pop.

Going back and re-reading your first post... do you have a light bulb limiter?

http://i23.photobucket.com/albums/b392/Structo/Lightbulb_Limiter.jpg

You should use one any time you fire up an amp during a build or after repair/maintenance to the power supply. It's easy to build if you don't have one. All you really need is an extension cord and a light bulb socket. The socket is wired in series on one side of the cord. The filament of the bulb (you must use an old school incandescent bulb - not the new fangled fluorescent type) acts as a current limiter. You can make fancier ones (mine has an outlet box and is mounted on a piece of 1x4 wood) but that is not necessary.

Under normal conditions when you switch the amp on plugged into the limiter the bulb will light up a bit and then dim down as the filter caps charge. If the light gets very bright and stays there you have a short circuit somewhere. The limiter can save you lots of trouble and costly repairs. After you test and things are okay you can unplug the amp from the limiter and plug it straight into the wall.

This is not just a handy tool to have. It is a "must have" item for your bench and you should always use it every time.

[Willabe]

Going back and re-reading your first post... do you have a light bulb limiter?

Yes, very good point, it is a must have tool.


               Brad