Progress of the Gretsch 6150 build

[hesamadman]

Ok guys. I started the build today. Just assembled the board. Since I didn't get any feedback on how I laid my board out before I assembled it, fingers are crossed that the changes I made will be sufficient for the build. I installed a 14 gauge solid piece of copper as my ground bus. I was going to ground each end of the bus to the chassis. Each component that goes to ground should shoot straight up to the ground buss. I assembled my layout in order like suggested. Input to power supply. I just installed 2 diodes like someone suggested instead of 4 like I originally had. First time using radial caps for my filtering. Hope this goes well because holy moly what a price break. I stuck with carbon comp resistors like the original amp and I used orange drops because I wanted to try them. I have not started to solder this layout yet. Im going to wait until some of my good pals on here say "go ahead man!!" 

Here is the board and layout.

[g-man]

Deleted

[hesamadman]

The only thing I noticed is the 470k is going to the wrong turret? Looks like a good start.

Yikes! Thanks for finding that, when I bent my bare wire around some of the turrets that are meant to be joined, I had some components pop out. I need to pay attention to where I put them back. ha

[g-man]

Deleted

[hesamadman]

Actually looking at it more closely, are the filter caps backwards?

I think so actually. Most definitely backwards.

[John]

I was going to ground each end of the bus to the chassis.

You only want to ground one end to the chassis, preferably right at the input jack. Merlin has a great article about grounding and what causes ground loops.

[eleventeen]

Actually looking at it more closely, are the filter caps backwards?

I think so actually. Most definitely backwards.

POP!!!

I used to work in a factory that assembled little CRT monitors...OEM things, like for ATM machines, those little ones for cash registers.

My job was to fix the bad ones. Sometimes the gals on the ass'y line would put in all their diodes backwards and I could fix 50 of the things a day. Unsolder, unsolder, flip, flip, solder, solder, done.

Anyway, about 50 feet away from me were two older women whose job it was to apply power and "smoke test" stuff right off the assembly line. Above them was a bare industrial ceiling, with foil-backed insulation. The foil was perforated with exploding cap holes punched through it, as if someone fired a shotgun upwards into it.

[HotBluePlates]

I guess you deleted the othe thread where you asked for input on your layout. I don't suppose this would materially change your end results, but attached is how I would do your layout.

It moves 3 parts off the board and to the input jacks, moves the 2.2kΩ grid stopper off the board and to the tube socket (where it really should be), adjusts the position of some resistors and caps so the signal doesn't cross over itself so much. Some of these have an atypical positioning of parts to minimize grid wire length. Also, the pots are rotated to sit the way they actually would be in your amp (lugs facing the open side).

[hesamadman]

I guess you deleted the othe thread where you asked for input on your layout. I don't suppose this would materially change your end results, but attached is how I would do your layout.

It moves 3 parts off the board and to the input jacks, moves the 2.2kΩ grid stopper off the board and to the tube socket (where it really should be), adjusts the position of some resistors and caps so the signal doesn't cross over itself so much. Some of these have an atypical positioning of parts to minimize grid wire length. Also, the pots are rotated to sit the way they actually would be in your amp (lugs facing the open side).

Holy crap dude. That's amaZing. How the heck did you do that so fast?

[HotBluePlates]

Several hours of drawing is actually taking a "long time" compared to others with more practice.

The drawing was done in Visio. Most of the shapes were already done by others & made available. I started to try to edit your drawing in MS Paint, but realized rearranging parts and making it look neat were incompatible.

[hesamadman]

Several hours of drawing is actually taking a "long time" compared to others with more practice.

The drawing was done in Visio. Most of the shapes were already done by others & made available. I started to try to edit your drawing in MS Paint, but realized rearranging parts and making it look neat were incompatible.

Its taken me many hours to get my layout. I appreciate your time. Thats awesome. After comparing the two I can understand why things you did make more sense. Im reading up on the grounding now. The article that was suggested has already proven to be informative.

[hesamadman]

Actually looking at it more closely, are the filter caps backwards?

I think so actually. Most definitely backwards.

POP!!!

I used to work in a factory that assembled little CRT monitors...OEM things, like for ATM machines, those little ones for cash registers.

My job was to fix the bad ones. Sometimes the gals on the ass'y line would put in all their diodes backwards and I could fix 50 of the things a day. Unsolder, unsolder, flip, flip, solder, solder, done.

Anyway, about 50 feet away from me were two older women whose job it was to apply power and "smoke test" stuff right off the assembly line. Above them was a bare industrial ceiling, with foil-backed insulation. The foil was perforated with exploding cap holes punched through it, as if someone fired a shotgun upwards into it.

Ha man I bet those women had many mini heart attacks

[Willabe]

Holy crap dude. That's amaZing. How the heck did you do that so fast?

The drawing was done in Visio. Most of the shapes were already done by others & made available.

Sluckey told you this in another thread you started.

And yes HBP is good at drawing/figuring out a layout but that's not his 1st rodeo.   

It takes practice, you'll get better but you also need to use a different program.


                 Brad      

[HotBluePlates]

Oh yeah... I should clarify the color scheme, as I didn't include dots to draw attention to solder joints.

The horizontal orange line is the ground buss, which you'll connect to the chassis over at the end closest to the power transformer. The green wires are ground wires that get soldered to the ground buss. Yellow wires are plate connections, blue wires are cathode connections. Red wires are grid wires, except for the dashed red wire, which is an underboard connection to B+. Black wires run from caps to the controls.

There is not a ground wire drawn from the jacks to the ground buss. If you use un-isolated Switchcraft jacks, the ground is already made to the chassis. If you use Cliff-style jacks (or isolate your Switchcraft jacks), you'll need to run a wire from the black wire at the jacks (connecting the ground lugs and switch lug) over to the ground buss at the preamp end.

The black wire on the Tone control is drawn as indicated on the schematic. Although the d.c. path is broken by the cap to ground, I don't really like that it is at an elevated d.c. voltage relative to the chassis. If it were my amp, I might add a cap between the board and the connection to the pot, or move the connection to the other side of the 0.01uF cap (to block all d.c. from the pot).

Also, the components at the jack are spread out to allow you to see the connections made. During an actual build, you'd bolt those jacks to a piece of material with holes spaced as they will sit in your chassis, orient the jacks as shown (relative to each other), and run the leg of the 1MΩ resistor through the 2 lugs on the Regular jack and 1 lug on the Treble jack. This resistor would point straight at you as you solder an end of the 100kΩ and 0.005uF/5000pF/0.0047uF/4700pF cap to their respective lugs. Then all 3 parts' free ends get twisted with the end of a wire, soldered, and heatshrink covering the joint.

Those parts should be light enough to stand each other up, but if you prefer, you can find insulated standoffs which have a single turret or lug to use instead. Likewise, the 2.2kΩ at the input stage grid can likely support itself, though you can use a standoff there too if you prefer.

The drawing doesn't depict the OT connecting to the 6V6 plate at pin 3, but I assume you know to make that connection, and from the other end of the OT to the 20uF filter cap.

[eleventeen]

Ha man I bet those women had many mini heart attacks

You would think, but they were 15-20 year veterans of caps blowing off.

I think it just made them meaner, LOL.

[hesamadman]

Oh yeah... I should clarify the color scheme, as I didn't include dots to draw attention to solder joints.

The horizontal orange line is the ground buss, which you'll connect to the chassis over at the end closest to the power transformer. The green wires are ground wires that get soldered to the ground buss. Yellow wires are plate connections, blue wires are cathode connections. Red wires are grid wires, except for the dashed red wire, which is an underboard connection to B+. Black wires run from caps to the controls.

There is not a ground wire drawn from the jacks to the ground buss. If you use un-isolated Switchcraft jacks, the ground is already made to the chassis. If you use Cliff-style jacks (or isolate your Switchcraft jacks), you'll need to run a wire from the black wire at the jacks (connecting the ground lugs and switch lug) over to the ground buss at the preamp end.

The black wire on the Tone control is drawn as indicated on the schematic. Although the d.c. path is broken by the cap to ground, I don't really like that it is at an elevated d.c. voltage relative to the chassis. If it were my amp, I might add a cap between the board and the connection to the pot, or move the connection to the other side of the 0.01uF cap (to block all d.c. from the pot).

Also, the components at the jack are spread out to allow you to see the connections made. During an actual build, you'd bolt those jacks to a piece of material with holes spaced as they will sit in your chassis, orient the jacks as shown (relative to each other), and run the leg of the 1MΩ resistor through the 2 lugs on the Regular jack and 1 lug on the Treble jack. This resistor would point straight at you as you solder an end of the 100kΩ and 0.005uF/5000pF/0.0047uF/4700pF cap to their respective lugs. Then all 3 parts' free ends get twisted with the end of a wire, soldered, and heatshrink covering the joint.

Those parts should be light enough to stand each other up, but if you prefer, you can find insulated standoffs which have a single turret or lug to use instead. Likewise, the 2.2kΩ at the input stage grid can likely support itself, though you can use a standoff there too if you prefer.

The drawing doesn't depict the OT connecting to the 6V6 plate at pin 3, but I assume you know to make that connection, and from the other end of the OT to the 20uF filter cap.

This is very thorough. I appreciate it very much. Can you explain to me the necessity of the regular jack being different from the treble jack?

[HotBluePlates]

Can you explain to me the necessity of the regular jack being different from the treble jack?

Well, it's what is shown in the Gretsch 6151 schematic you were working from.

The schematic shows a switched contact on the Regular jack, which is connected to ground.
The question you didn't ask was, "How do the jacks work?"

If you are not plugged into either jack, the grounded & switched contact on the Regular jack shorts its tip to ground. That also puts the input tube grid at ground potential through the 100kΩ and 2.2kΩ resistors, which prevents hum and background noise.

If you plug into the Regular jack, the tip is moved away from the grounded switched contact, and the path to ground is opened. The input signal sees a series 100kΩ and a 1MΩ to ground, which reduces the input signal to 91% its original strength. The 0.005uF cap is physically present but has one end not connected to anything in the circuit, so it does nothing when you're plugged into the Regular jack.

• The 2.2kΩ resistor is a series grid stopper which interacts with the input capacitance of the tube (along with the ~91kΩ of the parallel 100kΩ and 1MΩ) to roll off extreme high end, and mostly RF. This prevents your amp from picking up AM radio stations when you're in the city.

If you plug into the Treble jack, the guitar signal sees the 0.005uF cap first. After this is a 1MΩ to ground, but also the 100kΩ resistor at the Regular jack, which is a parallel path to ground by virtue of the closed switch contact on that jack. The 0.005uF cap and 91kΩ of total resistance to ground form a high-pass filter which is -3dB at ~350Hz which is mighty close to the 1st fret F on your high E string. Obviously, that is a string bass roll-off.

• The 2.2kΩ resistor still performs the same job as a series grid stopper, interacting with the same input capacitance of the tube and the ~91kΩ of the parallel 100kΩ and 1MΩ. Exact tube Miller capacitance depends on its gain at the chosen operating point, but if we estimate the total capacitance as around 100pF, it is a low-pass filter that's -3dB at ~17kHz and more loss above that.

So switched and non-switched jacks ae used so that each performs its proper function. Of note, speaker output jacks on Fender amps generally include 1 switched and 1 non-switched jack, again because each has a slightly different function.

[hesamadman]

Well guys…..heres how far I am on the Gretsch. Big chassis I know…….

[John]

Not a thing wrong with having more room than you need.

And besides, if the chassis/cabinet is bigger, people will think it's louder. 

[Willabe]

Looks pretty good overall but you have the pilot light where the input jack should be.


            Brad   

[HotBluePlates]

Looks pretty good overall but you have the pilot light where the input jack should be.

Agreed.

You might get lucky and not have hum. However, heater wiring is relatively big current compared to preamp signal wiring. Big a.c. (as measured by the number of amperes) creates a larger electromagnetic field around the wires than small a.c. If you have large electromagnetic or electrostatic fields around high impedance circuits (say couple-hundred kilohms to megohm range, like grid resistors), you risk inducing the a.c. signal into the high impedance circuit.

In other words, keep heater wiring away from anything in the input area, and keep large a.c. signals (or heater currents) away from much-lower level preamp stuff.

All this said, you could get lucky and have no hum. Or you might build 5 of these and the 5th one hums... You tear the amp apart to find out the pilot light by the input wiring caused hum in your 5th amp but not in the others. Good layout practices are mostly about not tempting fate... 

[hesamadman]

Hey everyone. Got the amp all hooked up………nothing. My 6.3v light comes on  

So I started at the beginning. Put my leads on the transformer. 530vac. Good to go there. So then I put my leads on the opposite sides of the diodes Because I noticed there wasn't a lot of voltage in my filter caps after I turned the amp off. Well….I wasn't getting much at all on the opposite end of the rectifier. Maybe under 10 vdc. I checked my diodes with my tester and both read the same. And I have them installed correctly. What in z world?!?!?!

EDIT….REFCTIFICATION IS FINE BUT FILTER CAPS ONLY HAVE ABOUT 25VDC IN THEM AFTRE AMP IS OFF>

[hesamadman]

OK I lied….rectification is good. Still no sound….I SHALL RETURN!!!

EDIT….REFCTIFICATION IS FINE BUT FILTER CAPS ONLY HAVE ABOUT 25VDC IN THEM AFTRE AMP IS OFF>

[HotBluePlates]

RECTIFICATION IS FINE BUT FILTER CAPS ONLY HAVE ABOUT 25VDC IN THEM AFTRE AMP IS OFF>

Lack of dc volts mean rectification is "not fine."

But that's okay. I'll tell you what I see in your pictures: You have a heavy copper wire for your ground buss on the board. You have 2 red wires from your PT to the rectifier diodes on the board. The red/yellow wire is bolted to the chassis. But I don't see a wire from the board's ground buss to the chassis.

The diodes won't rectify without a connection from the red/yellow wire to the - end of the filter caps and the board ground buss. That "connection can be a wire from the chassis to the ground buss, since you have the red/yellow wire attached to the chassis.

I also don't see any wiring to/from your controls, and don't know if you've done wiring since the pictures were taken.

[hesamadman]

RECTIFICATION IS FINE BUT FILTER CAPS ONLY HAVE ABOUT 25VDC IN THEM AFTRE AMP IS OFF>

Lack of dc volts mean rectification is "not fine."

But that's okay. I'll tell you what I see in your pictures: You have a heavy copper wire for your ground buss on the board. You have 2 red wires from your PT to the rectifier diodes on the board. The red/yellow wire is bolted to the chassis. But I don't see a wire from the board's ground buss to the chassis.

The diodes won't rectify without a connection from the red/yellow wire to the - end of the filter caps and the board ground buss. That "connection can be a wire from the chassis to the ground buss, since you have the red/yellow wire attached to the chassis.

I also don't see any wiring to/from your controls, and don't know if you've done wiring since the pictures were taken.

Sorry I should have updated the photo. I haven't yet. But I do have ground bus grounded to chassis. All controls are wired now. I was actually getting correct voltage on DC side of rectification as I checked again. What am I looking at as far as how much the filter caps will store. I know with my 50  watt amp they can store hundreds but this being a 5 watt amp, about how much should I be looking at. I always check their voltages before and after I drain them so I can be sure and the mid 20's is as high as the filter caps have been.

[HotBluePlates]

Put my leads on the transformer. 530vac.

... I was actually getting correct voltage on DC side of rectification as I checked again. What am I looking at as far as how much the filter caps will store. ...

I read 530vac as 265v-0-265v, which rectifies to 265v * 1.414 = ~374v after diode voltage drop. That is what you should see at the first filter cap with your amp on.

... What am I looking at as far as how much the filter caps will store. I know with my 50  watt amp they can store hundreds but this being a 5 watt amp, about how much should I be looking at. I always check their voltages before and after I drain them so I can be sure and the mid 20's is as high as the filter caps have been.

Ummm.... when you shut the amp off, you really want 0vdc on the filter caps.

Anything more than 0vdc is voltage just waiting to bite you when you go in the amp to do repairs or modifications. Fender put a pair of series 220kΩ resistors across the filter caps in their amps to drain the voltage to 0vdc when the amp was shut off.

Now ask me how much touching 470vdc sucked when my hand slipped in an old 50w Marshall... So if the amp works fine and your question is only about filter cap volts when you shut off the amp, I guess you can call it "amp done."

[hesamadman]

Put my leads on the transformer. 530vac.

... I was actually getting correct voltage on DC side of rectification as I checked again. What am I looking at as far as how much the filter caps will store. ...

I read 530vac as 265v-0-265v, which rectifies to 265v * 1.414 = ~374v after diode voltage drop. That is what you should see at the first filter cap with your amp on.

... What am I looking at as far as how much the filter caps will store. I know with my 50  watt amp they can store hundreds but this being a 5 watt amp, about how much should I be looking at. I always check their voltages before and after I drain them so I can be sure and the mid 20's is as high as the filter caps have been.

Ummm.... when you shut the amp off, you really want 0vdc on the filter caps.

Anything more than 0vdc is voltage just waiting to bite you when you go in the amp to do repairs or modifications. Fender put a pair of series 220kΩ resistors across the filter caps in their amps to drain the voltage to 0vdc when the amp was shut off.

Now ask me how much touching 470vdc sucked when my hand slipped in an old 50w Marshall... So if the amp works fine and your question is only about filter cap volts when you shut off the amp, I guess you can call it "amp done."

I was just under the assumption that most amps store a charge for some time once turned off. But better news. I screwed up the inputs.  Once I reworked them…I got some tone. Some sweet tone too. Now I used alligator clips on the inputs to get them where they were correct with the layout. So I got sound out of the tele jack. Its has LOTS of noise and by adjusting either the tone or volume…I either make it better or worse. The regular jack on the other hand…I don't get any guitar….just tons of noise. So maybe my inputs are still wrong..

Now it was suggested that I move my heater wires since they are so close to my input. I drilled my dang chassis before I installed the board and I did a ton of stuff backwards. Guys said it may or may not interfere. So since there was a chance of it NOT interfering I went ahead and rolled with it. Now it may be the cause for some of the noise but I doubt its the entire culprit. In the photo you will notice that I used shielded wire from my input….ran it high overhead of the board and hit my 12ax7. I grounded the shield the same place as I grounded my input jacks.

Image: http://www.rdksounddesign.com/projects/photo-3.JPG

[hesamadman]

Also…..the orange drop on my tone knob goes to ground. The place in which its positioned on the ground bus…..how big of a mistake is that. its a little further ahead on the bus than the layout suggests..

[SILVERGUN]

Well Buddy,,,where do we start?

We'll need a clear picture of the complete inside of the chassis... and then tube voltages
There are some glaring issues, and no-one here wants to be the one to tell you that you F'd up  

It also takes a lot of time to fix you're way of seeing the whole picture....you have to break it all down to one section of the circuit at a time until you have eliminated EVERY possible component,,,and you are left with a solid, working build......no one can do this for you.

But, since we're old friends, I'll step up, and TRY to help...I just don't have a ton of time

Troubleshooting is WAR..it's YOU against the problem(s).......have you prepared yourself for troubleshooting war?
-Do you understand how the amp works?
-Do you fully understand your schematic?

You'll have to do exactly what is asked of you, and give clear, honest answers.....just like a good soldier.

Luckily, you have a VERY simple circuit in front of you.........this could be a very short war.

Also…..the orange drop on my tone knob goes to ground. The place in which its positioned on the ground bus…..how big of a mistake is that. its a little further ahead on the bus than the layout suggests..

Remove it from the ground buss....what happened?

It's MUCH less of a mistake than your input wire that travels all the way across the amp to V1 and then sloppily connects to that resistor that has too much leads showing on each side of the resistor body....
Do you see what I see?....YOU have to be able to see that as a problem, brother...

I'd love to see you fix the chassis layout and move the indicator and power switch over to where you currently have the input jack,,,,and then move the input jack over to the other side and separate your AC layout completely from your signal layout .........and be able to shorten up that input wire...etc., etc., etc., etc., etc.,

 
No sugar coating there Sir....
4 months ago(?) WE found a missing wire under your board.....what's it gonna be this time?

WE ALL MAKE MISTAKES....EVERY BUILD IS A NEW OPPORTUNITY TO LEARN SOMETHING
THIS IS A BIG OPPORTUNITY FOR YOU TO FIX YOUR OWN AMP, AND LEARN HOW AND WHY IN THE MEANTIME
Start looking at the amp in smaller sections and tell us what you are checking and why....start at the input and then work your way from left to right on the schematic, until you have verified that you have everything 100% correct....
Every time you confirm a correct connection and an accurate component value, highlight it on the schematic and move on until you have verified every single connection and every single component value.....that's how you do it when you don't know how to guess what you're looking for by being able to translate what you're hearing into where it might be coming from.

Good luck sir....you got this.

[terminalgs]

noise reduction:

It looks like you may have mounted your transformers with the laminations in parallel.  A common practice to reduce noise and hum is to set one at an opposite orientation from the other.  If this is the case with your build, it wouldn't be hard to rotate the OT 90deg (you might have to drill four more holes...)

I can't remember which PT you selected, but I don't see a center tap wire for the filament winding.  Do you have an artificial center tap somewhere?  If not, be sure to add one, and connect to the cathode of the power tube.  Lots of people connect to chassis ground, which is fine, but the most amount of noise reduction will come from connecting the CT to the power tube's cathode (heater elevation).  If there isn't a CT of some sort, you'll have tremendous noise.

personally, I'd move the fuse holder to the other side of the IEC mains to remove it from proximity to the OT's output wires (as long as you have your unibit in chuck for the OT rotation job...)

[HotBluePlates]

I was just under the assumption that most amps store a charge for some time once turned off.

They do, but you don't want them to. So you add something like a bleeder resistor to ensure they do not store a charge when turned off.

... I screwed up the inputs.  ...

Now it was suggested that I move my heater wires since they are so close to my input. I drilled my dang chassis before I installed the board and I did a ton of stuff backwards. Guys said it may or may not interfere. So since there was a chance of it NOT interfering I went ahead and rolled with it. ...

Well, maybe we ween't firm enough the first time around...

Picture this: God got you backwards when he built you. No biggie, most things are in the right place. But you anus is on your head above your chin, and your mouth is below your tailbone. How well does that works for ya? You might not have a problem, or maybe you will...

 

Just kidding. But Your noise could be where the jacks are, but most likely is due to the lash-up in the photo. I'm kinda banking on lash-up jack wiring that doesn't match what I drew on the layout. You should be aware that I assumed that at some place you would have a circuit ground attached to the chassis, and that the 3 lugs connected with the black wire (on the jacks) presumes an additional connection to ground. With Switchcraft jacks, if the chassis is grounded, the connection is automatically made by the jacks unless you go out of your way to isolate the jacks from the chassis.

So be sure to verify that with nothing plugged in the jacks that the hot of the Regular jack has continuity to ground. If that's good, try unsoldering/disconnecting a leg of the 0.005uF cap from the Treble jack to the 1MΩ resistor; pick the leg that connects to the 1MΩ resistor, and not the Treble jack itself. Does the noise go away?

Either way, bite the bullet, use a hole plug or cover plate, re-drill, and put things in the right place. We've all done it, and we all have ugly projects that are sacrifices on the altar of learning.

[hesamadman]

Ok. So I just learned how to find old threads that you've started. Apologies for making so may new ones. So. Here I am with my Gretsch 5 water!


Had some extreme humming. Got worse when volume was turned up. So... lead us all to believe that it was before the volume control. The only thing before the volume control is the first half of the first triode. I did a few things that were suggested and still had the hum. I even completely disconnected the input jacks. Still had it.


I am curious though if even though the issue seams to be before the volume control, is it possible that the grounding could still be an issue. It is a heavily painted chassis. I could probably have grinder the pain off better under my ground terminals and inputs and pots. Another reason I am suspecting ground issues (and someone correct me if this isn't likely), when i turned on the amp once, i had zero volume. I reached to grab the volume pot to turn it up, and as soon as my hand made contact on the bare metal of the pot..SUDDENLY SOUND. So that made me think that it had a poor ground and my body gave it the jump start of ground it needed. (kind of like a receptacle in a home that has a loose neutral wire. may not be making good contact but as soon as you plug something in that allows a higher number of amps...suddenly that connection seams to kind of arc and make necessary contact to complete the circuit.)


  

[hesamadman]

Bought a Dremal. Grinded down the inside of chassis where pots and inputs are installed. Also grinder down a new spot to put my ground lug I'm using for the center tap of xfmr and ground bus connection.

[hesamadman]

Gretsch build is finished. Sounding great. Only one thing.


I wasnt able to stop the noise when the tone knob is all the way down. I was wondering if an easy fix would be to put a small resistor in series with the left pin of the pot so that when its all the way turned down, the resistance will be just high enough to stop the noise. So basically just not letting the tone knob reach such low resistance as when its turned completely down. Since there is B+ on this pot, i measured it. Its at 158 when the pot is turned to any position. But that last little hair before its all the wy down, its drops to 138....and thats when the noise happens.

[sluckey]

Since there is B+ on this pot, i measured it. Its at 158 when the pot is turned to any position. But that last little hair before its all the wy down, its drops to 138....and thats when the noise happens.

That voltage should not drop at all! The pot wiper is probably partially shorting to the pot body (ground) when turned to that extreme end and the resulting arc is causing the noise. The easy solution would be to move the black wire from the top end of that orange .01 cap to the bottom end of the orange .01 cap. (IOW, the pot will be connected to pin 5 of the big tube rather than pin 6 of the little tube.) Then there will be no dc on the pot.

EDIT... Just move the cap on the pot like this pic. Then there will be no dc on the pot.

[hesamadman]

Awesome Sluckey. Thanks. I'll do that!

[hesamadman]

Well. All that I tried was unsuccessful in removing the noise when the tone pot was turned all the way down. I returned the pot layout like the original schematic and tried something that Ive been thinking I would try. I put a 1k resistor on the pot. Basically raising the overall value of the pot (which is 500k) to 501K. And raising the lowest value from 2ohm to 1.02k ohms. This stopped the noise. It gives me a little less room to work the amps tone pot but I couldnt imagine playing it with it down that low anyway. It sounds great this way actually.


In addition I added a 10uf cap in parallel to the 35uf cap on the pin 3 cathode. Gave it a nice bottom end boost. Also took the cathode resistor down to 1k instead of 1.5k. Getting a great tone im surprised.


More info to come guys. Thanks again!

[billcreller]

I thought that schematic number (6150) looked familiar.  I built one some years back.  Had my share of noise problems with it. The thread is likely on here some place (?)  I have a pic of it, but can't seem to get it on here (?)

[TeslaRect5150]

Hey there,
     That .01 coupling cap from your 2nd 12ax7 stage to the power tube is there to block the D.C. voltage on the plate and allow only A.C. signal through to the volume/tone controls. Having DC high voltage on your controls is very dangerous to you and whoever else uses your amp. The arcing could have damaged your tone potentiometer. Try a new pot and wire the tone control so it doesn't have DC high voltage on it. I've made this same mistake before also.
Please change the wiring to after the coupling cap.
Looking at the schematic now, and another option is forget about wiring it after the coupling cap and just connect the tone control over to the middle lug of the volume pot. This puts the tone control after the volume control and before the second half of your 12ax7. I have a feeling this is how the amp was intended to be wired in the first place, and the schematic is in error. Although I have never seen the inside of an original, so I can't say for sure. I do know that DC on your tone controls is no good though.
Hope this helps. Be extremely careful, getting shocked is no fun.


My .02 cents
Peace,

Aaron

[hesamadman]

I thought that schematic number (6150) looked familiar.  I built one some years back.  Had my share of noise problems with it. The thread is likely on here some place (?)  I have a pic of it, but can't seem to get it on here (?)

Hey Bill. Did you make any changes to your build in comparison to the schematic? What sort of things did you do to stop your noise issues?

[hesamadman]

Hey there,
     That .01 coupling cap from your 2nd 12ax7 stage to the power tube is there to block the D.C. voltage on the plate and allow only A.C. signal through to the volume/tone controls. Having DC high voltage on your controls is very dangerous to you and whoever else uses your amp. The arcing could have damaged your tone potentiometer. Try a new pot and wire the tone control so it doesn't have DC high voltage on it. I've made this same mistake before also.
Please change the wiring to after the coupling cap.
Looking at the schematic now, and another option is forget about wiring it after the coupling cap and just connect the tone control over to the middle lug of the volume pot. This puts the tone control after the volume control and before the second half of your 12ax7. I have a feeling this is how the amp was intended to be wired in the first place, and the schematic is in error. Although I have never seen the inside of an original, so I can't say for sure. I do know that DC on your tone controls is no good though.
Hope this helps. Be extremely careful, getting shocked is no fun.


My .02 cents
Peace,

Aaron

I appreciate it. Im going to try to fix that now.

[hesamadman]

Hey there,
     That .01 coupling cap from your 2nd 12ax7 stage to the power tube is there to block the D.C. voltage on the plate and allow only A.C. signal through to the volume/tone controls. Having DC high voltage on your controls is very dangerous to you and whoever else uses your amp. The arcing could have damaged your tone potentiometer. Try a new pot and wire the tone control so it doesn't have DC high voltage on it. I've made this same mistake before also.
Please change the wiring to after the coupling cap.
Looking at the schematic now, and another option is forget about wiring it after the coupling cap and just connect the tone control over to the middle lug of the volume pot. This puts the tone control after the volume control and before the second half of your 12ax7. I have a feeling this is how the amp was intended to be wired in the first place, and the schematic is in error. Although I have never seen the inside of an original, so I can't say for sure. I do know that DC on your tone controls is no good though.
Hope this helps. Be extremely careful, getting shocked is no fun.


My .02 cents
Peace,

Aaron

The simplest fix was to put the tone knob after the coupling cap. That took the B+ off the tone knob. Thanks for that bit of input.

[TeslaRect5150]

I'm glad this helped out. Enjoy your build my friend. Always a great feeling. 
Peace,
Aaron