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 Post subject: Re: New Tweed Build!
PostPosted: Thu Dec 19, 2019 12:10 am 
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Location: Shawnee, OK
If you can, clip a lead of the multimeter to a VAC connection and for VDC clip a negative lead to Chassis or Ground, then sit on one hand and use the other test lead with the other hand. That keeps the current from traveling from crossing one hand to the other with your heart in between :bugeye: . It's scary at first and should stay scary anytime thereafter. Use caution, but don't let it paralyze you.

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 Post subject: Re: New Tweed Build!
PostPosted: Wed May 13, 2020 8:21 am 
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Wow how time flies. The new year rolled around and the guitar portion of my project kicked in and and kept me occupied. I'm working with a local Luthier building a telecaster and having a blast... until COVID. So with that shut down for a couple months I decided to start in on the cabinet build. I still haven't mustered up the courage to test my amp yet... really need to do that. I've included a photo of the cabinet build though, hope to upholster the speaker baffle tonight. I think the natural maple looks amazing, I'd never done box joints before and they turned out alright... plan is to paint the cab to match the theme of my guitar build but right now I just like looking at the natural finish.


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Image from iOS (10).jpg [ 922.89 KiB | Viewed 481 times ]
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 Post subject: Re: New Tweed Build!
PostPosted: Wed May 13, 2020 1:25 pm 
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Good to hear from you again :thumbsup: Cabinet looks good, first time building one? Box joints look good and strong.

As far as testing the amp, do you have insulated clip-on leads? The main thing to avoid is using BOTH hands when testing and where possible use both of the clip-on leads. Read MitchM's reply on this guy's build about testing viewtopic.php?f=11&t=6591

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 Post subject: Re: New Tweed Build!
PostPosted: Thu May 14, 2020 8:16 am 
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First time amp build and cabinet build, so far so good. Got the speaker baffle covered last night... not entirely happy with the result. Hard to get the right tension across both sides and not warp the pattern. I used a hair dryer to warm up the material and that helped get it wrapped around the wood better. It is nice and taut though so I've got that going for me :).

I've only ever really dealt with low voltage electronics before so the clips I do use are not a terribly thick gauge, they are just cheap ones from Sayal that look like the attached. I usually just clip those on to the end of my probs... I think I'll look for clips that plug right in the meter and not screw around with these cheap ones. I also read MitchM's response and it's helpful, I should be able to sort those measurements out.

I also need to round over the edges on that cabinet and build the back panels. Looking forward to trying to get the radius right on the lower panel.


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Alligator-Clip-Test-Line-Wire-Set-Insulated-Test-Cable-Double-Ended-Clips-Alligator-Clip-Battery-Cable-Alligator-Clip-Wire.jpg
Alligator-Clip-Test-Line-Wire-Set-Insulated-Test-Cable-Double-Ended-Clips-Alligator-Clip-Battery-Cable-Alligator-Clip-Wire.jpg [ 11.49 KiB | Viewed 469 times ]
8AC46A6A-18FF-423F-95FD-4F28B5EF205B.JPG
8AC46A6A-18FF-423F-95FD-4F28B5EF205B.JPG [ 2.16 MiB | Viewed 469 times ]
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 Post subject: Re: New Tweed Build!
PostPosted: Thu May 14, 2020 1:01 pm 
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+1 on on meter probe/clips. Be sure not to get the cheapest ones. When my Craftsman MM went south on me, I bought an Amprobe AM 560 (subsidiary of Fluke)which included both pointed and clip probes. Was fairly reasonable on Amazon, although I've heard A-zon doesn't ship to the Great White North.

Coco posted his trick for grill cloth somewhere, but can't find the link. I seem to remember that it involved folding, squaring up and stapling the cloth along the top edge, then taking 2 lengths of wood (1x2) and clamping the cloth between them. That way you could pull the cloth evenly around the bottom of the baffle to the back and staple the cloth. Hope that makes sense. When I did the roundover on my cab,I used a 1/4' roundover bit, so if I didn't like it I could step up to a 1/2". Liked and left it at 1/4". BTW, here's a link to 5E3 cabinet plans at Modulus Amplification https://modulusamplification.com/DIY_DOWNLOADS-W4.aspx

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 Post subject: Re: New Tweed Build!
PostPosted: Fri May 15, 2020 9:42 am 
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We've got our own Amazon.ca up here but with an entirely different and higher priced inventory :). We can order from the .com though, Prime doesn't work for free shipping and we may get whacked with duty. Things are starting to slowly re-open around here and hardware stores are one of the ones doing so. I've got a Princess Auto close to me I may venture out to on the weekend, they've got some clip's that look like they attache to the end of my probs I'll give a try.

That cabinet plans are the same ones I used to build my cab, the 3" radius on the lower back panel took some figuring out but I got it cut last night so the cab is about 95% ready for paint... just need to cut and attach the cleats.

I also watched a video where part of the baffle was clamped down to aid in stretching the material... unfortunately when I made my baffle I built it in a way that you insert the speaker through the baffle and then fasten the speaker to the baffle so it needs to be attached when I upholster. I may cut a new baffle and try again... not sure how crazy the waviness of the material will make me. Also considering different colour upholstery too.


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 Post subject: Re: New Tweed Build!
PostPosted: Fri May 15, 2020 11:46 am 
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Keep on plugging along. :thumbsup: I got discouraged back circa 2010 when I was building AX84 amps, then I found Trinity when I retired. Between the the two, I ahve learned a lot , but there are still gaps to be filled in my knowledge :bugeye:

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 Post subject: Re: New Tweed Build!
PostPosted: Sat May 16, 2020 6:28 pm 
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Well, I did some measurements... turned things on with no tubes plugged in...
5Y3 - Pin 4 and Pin 6 - 727VAC
5Y3 - Pin 4 and Chassis Ground - 364
5Y3 - Pin 6 and Chassis Ground - 364
5Y3 - Pin 2 and Pin 8 - 5.66VAC
V4 - Pin 2 and Pin 7 - 6.45VAC
V3 - Pin 2 and Pin 7 - 6.45VAC
V2 - Pin 4-5 and Pin 9 - 6.44VAC
V1 - Pin 4-5 and Pin 9 - 6.44VAC

Lot's more measuring to do and assuming the above measurements are alright soon time to plug some tubes in I think

A few questions first...

First, Page 52 of the guide leads with "DO NOT OPERATE YOUR AMP WITHOUT A LOAD". I'm not quite sure what that means... I have no tube's plugged in, but is operating it simply turning it on? Does the load come once the speaker is plugged in?

Second, I understand the important thing to do before working on the amp is to discharge the capacitors, if I'm reading the manual correctly I believe I don't need to manually do this, I can follow the directions of unplugging the amp, placing the Standby and Power switches into the On position for 30 seconds and then measuring between chassis ground and the positive leads on the 3 capacitors to ensure they read 0... then I should be safe to poke around if I need to. Am I understanding that right?

Thirdly, on step 2, "Test the filament voltages and ensure they are on the correct pins for all tubes." what are the filament voltages? Is that a matter of referring to the schematics to determine all the pins to be testing?


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 Post subject: Re: New Tweed Build!
PostPosted: Sat May 16, 2020 9:11 pm 
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1) Load is connecting a speaker. When you install the tubes, make sure you're plugged into a speaker. Otherwise, you can blow the transformer. Not an issue without the tubes
2) I would power off, unplug and then turn power back on to discharge the caps.
3) a)Filaments = heaters, for power, phase inverter and pre-amp tubes, also the two pins at the pilot light. Rectifier tube DOES not have a filament. Voltage with no tubes should be around 7 VAC, around 6.3 VAC with tubes. Filaments "heat" the cathode plate, causing it to emit electrons. b) Yes, check the tube diagrams and/or the layout. Pin 4 or 5 and 9 on the nine pin (noval) sockets, pins 2 and 7 on eight pin (octal) sockets. Should be the red and black wires. Now that I read your post again, you've already checked them :!: c)Just make sure the red and the black wire are on the same pins down the line, that is, black on 4 and 5; and red on 9; black on 7 and red on 2 (or vice versa), as long as it's consistent.
Oops, "splaining" too much again.

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 Post subject: Re: New Tweed Build!
PostPosted: Sat May 16, 2020 9:39 pm 
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Reread your voltages again. On rectifier, check voltage between pin 8 and ground using VDC setting. The rectifier is converting AC current to DC at that point, this is the B+ voltage. It should be 400 volts DC or above with no tubes.

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 Post subject: Re: New Tweed Build!
PostPosted: Sun May 17, 2020 10:56 am 
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Readings look really close

V1
Pin 1 - 126
Pin 3 - 1.92
Pin 6 - 129
Pin 8 - 2

V2
Pin 1 - 159
Pin 3 - 1.21
Pin 6 - 200
Pin 7 - 16
Pin 8 - 44

V3
Pin 3 - 361
Pin 4 - 331
Pin 8 - 21

V4
Pin 3 - 359
Pin 4 - 331
Pin 8 - 21

The only one that looks out of spec is V2 running low on pins 3,7,8 and high on pin 1.

I proceeded through the steps... and what do you know... I'm making music... holy frig... am I ever pleased :) Now to finish this cabinet so I can really start rocking!


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 Post subject: Re: New Tweed Build!
PostPosted: Sun May 17, 2020 1:52 pm 
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Are you using the Sovtek or JJ 5Y3 rectifier tube? Makes a difference in voltages per voltage chart and those voltages dependent on mains (line) voltage. That being said, looks good on voltages either way and the proof is IT WORKS :thumbsup: :!: :thumbsup: Congrats :D

PS Are you liking the sound?

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 Post subject: Re: New Tweed Build!
PostPosted: Tue May 19, 2020 8:03 am 
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It is the JJ 5Y3... I am enjoying the sound for sure... I don't have it all assembled in the cabinet yet, it's just sitting on the bench, but I'm happy. Cabinet is primed and I'm waiting on some more paint to finish the stencilling as well as a change in grill cloth to better match the cabinet artwork. I've only ever played my electric with an old Vox "Brian May" practice amp, so this one is a real step up. I hope to post pictures of the finished project soon... though it did take me almost 5 months to get back to it the last time, hopefully I will get back to it quicker than that.

I think I found the post you were referring to from Coco:

viewtopic.php?f=16&t=2205&p=22427&hilit=cloth#p22427

I'm not sure I'm following though. Off to google some video's on stretching cloth :)


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 Post subject: Re: New Tweed Build!
PostPosted: Mon Jun 08, 2020 7:34 pm 
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Time for some trouble shooting help... got the amp mounted in the cabinet and things sound good... loud... holy smokes... my little practice amp did not prepare me for how loud a real amp could sound! Things sound great for a bit, but once the amp gets warmed up I start to get some crackling coming through... this is with the guitar plugged and volume off on the guitar, or with guitar unplugged same noise... I've attached it here to see if it sound familiar. This sound is not here when I first turn it on. (Rename tweed.zip to tweed,m4a to play it)

Also showing my inexperience with tube amps... how warm is too warm :) I'm surprised at how warm this gets after a couple of minutes. The 3 big tubes are do have a red glow to them... not sure how red is too red... like I wouldn't want to touch the glass, I can feel heat radiating off of them.


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 Post subject: Re: New Tweed Build!
PostPosted: Tue Jun 09, 2020 4:20 am 
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It's normal for tubes like 6V6 and 5Y3 to run too hot to touch. 12AX7 and 12AY7 just get warm. It could still be uncomfortable to touch them, though. You shouldn't see a red glow in any tube. Just the normal orange glow from the heater. The orange glow is harder to see in small tubes, but it can be quite bright in larger ones.

The large dark grey or black metal parts inside tubes are the plates. If you see any red glow on a plate it's a bad sign. This is known as "red plating." It means the tube is being driven outside its limits and if the condition continues it will burn out.

All the voltages you posted earlier are within spec, so you shouldn't have any red plating issues. You should check the voltages again to make sure.

As for the crackling, it sounds like a bad solder connection that gets worse once things warm up inside the chassis. Have a good look at all your solder connections and see if any of them look dull or grainy.

You can also use something long, thin, and insulated to carefully poke all the connections and wires to see if you can make the problem appear or go away. A chopstick is ideal for this. Don't use a pencil because the graphite inside it conducts electricity.

If you hear the crackling with the volume controls turned all the way down, that means the problem is somewhere after the volume controls. If the volume controls can make the crackling louder or quieter that means the problem is before the volume controls.

There's a chance it's a bad tube, too, but this is unlikely.


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 Post subject: Re: New Tweed Build!
PostPosted: Tue Jun 09, 2020 8:28 am 
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Some Tips

Tube Amp Troubleshooting

Take voltage readings of your tubes in case someone on the forum needs to see those readings.
Voltage readings are like heart beat and blood pressure readings that your doctor uses to diagnose your health issues.
The tubes need to be in the amp, the amp needs to be on and the power tubes biased properly to get any sort of meaningful voltage readings


For the most part, an amp is basic triode gain stages put together in different sequences.

The checklist below doesn't cover everything but it is something to always bear in mind, whether you're fixing an existing amp or troubleshooting your own build.

With tubes installed, measure and record all the voltages and compare them to whatever documentation you have. High plate voltages or low cathode voltages indicate the tube is not conducting properly. Could be a bad plate or cathode resistor, poor ground, bad bypass capacitor or vacuum tube.

Use FX loops if present to isolate a problem to preamp or PI/output. Then is the noise affected by a MV? Tone stack? Channel volumes?

Pull preamp tube 1, turn on amp and see if problem has gone. If so, focus in this area. If not resolved, pull tube 2 and repeat. This will help isolate the location of preamp issues. If the problem goes away, try replacing that tube.

Once you narrow it down to a single triode or maybe two possible triodes, here's a checklist of things a triode needs to function, aside from making sure it's not just a bad tube:

1) Plate resistor.

2) Cathode resistor, bypassed or not. The bypass cap is always suspect.

3) Grid leak resistance. This may be a volume pot, a fixed resistor, or a tone stack. No matter how it's accomplished, the grid must have a connection to ground for current to flow. And ensure the grid leak is always there, even if a switch connected to the grid is engaged ("It pops when I change channels")

4) In AC coupled triode stages (the vast majority) make sure no DC is leaking from the previous stage to the grid.

Confirm that 1-3 are connected and measure ok with an ohmmeter.

Measure 4 with a voltmeter.

Measure voltages at plates and cathodes. If there isn't a big voltage drop across the plate resistor, the tube isn't conducting. One of the four issues above is the cause. Even if they all check ok as far as measured resistance goes when the amp is off, something isn't passing current. For example, it could be a bad ground connection not allowing current to flow so voltages are way off, such as very high plate voltages.

With no HT voltage (completely discharged safely) , all anode resistors need checking and cathode capacitors (25uF 50V etc) might require replacing.


Other Tests
Check all ground connections to ensure they are solid, clean and conductive. Measure resistance <1 ohm.

Noise or cracking.

Crackle could be caused by any resistor. Grounding grids or pulling tubes lets you find the stage where the crackle is.

First track down where the crackle is coming from. Either by grounding grids or pulling preamp tubes, working from input to PI. Pull tubes starting with the first preamp tube until the noise goes away. That narrows down the problematic area. Try replacing the tube first before diving in.
Check value/integrity of plate resistor.

Then it's a combination of the above list, the way the amp was constructed, and materials used. In eyelet/turret/tag/terminal builds, solder joints are pretty easy to inspect. Touch up suspect solder joints by reheating and adding a little solder.
Look for discolored components. Smell things.
Measure any voltage from the board material itself to ground!

LEAD DRESS

Try to maintain a linear path for audio. Think of the signal levels in each wire as you route them. Keep inputs or low level signals away from high level wires. When in doubt, use shielded wire.

Twist heater wires. What is really important is the distance of the heaters to the input grid wires.
You can fly the heater wires in the air & away from the chassis and place the the grid wires against the chassis. Or if you wish to go the other way fly the grid wires in the air & away from the chassis and place the the heater wires against the chassis in the corner.

Don't have your OT's input and output wires run parallel to each other in close proximity for anything more than is unavoidable. And the reason is RF interference via induction. Twist the input and output side for common mode noise rejection. Even a few turns will help quite a bit.
The closer together they are, and the longer the run that they are together, especially with no twist, will lead to noise.

If you must cross a signal wire with another wire try and cross it at 90-degrees to minimize inductive interference.

Keep high signal lines away from low. If you must cross them, do it at 90 deg. Every lead has a magnetic field. If you have an alternating current in one it can induce a current in an adjacent wire. Parallel lines make this worse, 90 deg should minimize it. Same as the transformers; they’re nearly always 90 degrees out (on their cores).

Identify which leads carry AC and which DC and keep AC runs short and let DC runs be longer. Audio signal is AC.
Twist all AC wires if possible for as much of the length they run as possible; even a few turns cuts down RF noise (common-mode-suppression) Power leads, rectifier and heater leads and remember: your OT wiring is AC as is any wiring running to, or from, a transformer, and that includes the choke.

Typical amp has short DC path from tube to tonestack components then three long AC paths to the pots. If you have the components right by the pots then you have a single longer DC path from the tube and short AC paths.

NOTE - Measuring "continuity" is NOT a guarantee of determining a short. The "continuity" setting on a multimeter typically generates a tone when the measured resistance is 199 ohms and less. That last statement is very, very important to understand. As an example, if you are measuring the continuity of a wire or switch contact or ground connection and a tone is created, this indicates that the resistance between the leads is somewhere between 0 ohms and 199 ohms. That is potentially NOT a short. For an accurate determination of a short, you'll have to switch to a resistance setting and measure the actual resistance.

TIP: Sometimes a larger diameter solder is needed (especially for ground connections). Instead of buying an entire roll, a quick solution is to just twist together two strands of the smaller stuff. A simple rolling between the fingers is usually sufficient to get a tight twist.

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 Post subject: Re: New Tweed Build!
PostPosted: Tue Jun 09, 2020 12:16 pm 
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Thanks mitch and coco... will dig in to some trouble shooting tonight hopefully... most of what coco has included I don't understand, so googling will be required to find out what the majority of it means!


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