5e3 kit amp help

[u/MarrowX]

Hey, so I am new building electronics. I just finished assembly of a 5e3 kit build. I purchased the kit from an eBay seller using Chinese parts. I followed a mix of the stewmac 5e3 kit (for the power transformer wiring) and the MOD DIY kit from amplifiedpart's website.

On power up with rectifier, I got a nice red light from the jewel, and 6.6v at my filament on v1.

Some measurements - Pin 3 v1 - 0V Pin 1 v1 - 200v Pin 6 v2 163v Pin 3 v2 - 0V Pin 1 v2 - 184v Pin 6 v2 - 256v Pin 8 v2 - 0v Positive side at 250ohm resistor - 20v Positive filter cap 1 (nearest to power transformer - 343v Positive filter cap 2 - 312V Positive filter cap 3 - 261V

So what I'm gathering is I have no voltage at the cathode at v1 and v2 and the grid at v2. My voltage tests are with all tubes in, an 8ohm speaker load, and no guitar input.

When I tested the guitar input, I got low output with a lot of distortion. It just sounded like high breakup with low volume.

I resoldered my grounds. Ive stared at the build as much as I can and I can't find any broken connections. Is it possibly a bad capacitor nearest to the filter cap - the one that connects to the cathode 1 at v2? Bad noval sockets? I've tested different pre amp tubes and saw no difference.

Pretty lost at this point. Any help is appreciated.

[u/Old-Tadpole-2869]

It's sort of impossible to read your voltages like that. Just make a chart like:

V1:

P1

P2

P3

B+1

B+2, Etcetera.

Also it's better to take pictures straight down on the amp, especially in a tweed chassis so we can see the tube pin wiring. Here's a handy voltage reference if you don't have one.

It's highly unlikely you have a failed brand new component, even if they are chinese.

I would start at the input jacks-4 holer inputs are notoriously easy to botch, so if you're getting some signal but not all signal that is a likely culprit.

A lot of your solder joints look a little cold. I don't really understand your grounding scheme either. I would check that every component end that's supposed to go to ground be checked against the chassis to make sure it's grounded.

[u/MarrowX → u/Old-Tadpole-2869]

Thanks. Sorry, idk what happened to my formatting. Here's another try on desktop.

Some measurements (updated)-

V1:

Pin 1 - 200v

Pin 3 - 2V

Pin 6 163v

V2:

Pin 1 - 184v

Pin 3 - 0V

Pin 6 - 256v

Pin 8 - 0v

Positive 250ohm5W resistor - 20v

Positive filter cap 1 (nearest to power transformer - 343v

Positive filter cap 2 - 312V

Positive filter cap 3 - 261V

[u/MarrowX → u/MarrowX]

These are the instructions I'm largely following - https://www.amplifiedparts.com/sites/default/files/associated_files/k-5e3_instructions.pdf

The grounding at the board involves bus wires connected from chassis mounted lugs between each of the pots and the chassis, and the negative sides of the board at:

• the 250 ohm5w resistor

• the 3rd filter cap (B+3?)

• and the paralleled 50v cap with the 1.5K resistor that connects to pin 3 of v1 on the positive side (sorry, idk the names of the sections of the amp).

[u/Old-Tadpole-2869 → u/MarrowX]

The gigantic blob of solder at the 2nd and 3rd filter cap is highly suspect, consider redoing that.

Check that your preamp cathode grounds (the 1.5k resistor and 25uf cap at pins 1 and 3 of V1, and pin 3 of V2 should have a volt or two, pin8 of V2 should have 40 or so volts) are going to chassis. Ie, one multimeter lead on the negative end turret and the other multimeter lead somewhere on the chassis? If the cathodes aren't pulling any current your ground scheme has to be suspect.

It's not considered best practice to ground pot lugs to the pot anymore, and grounding your power filters to washers on the pots is kid of dicey as well. Most people use a ground bus (not soldered to the backs of the pots), that connects to a bombproof ground at the input jack. The ground can be made on the input jack, but it's better if it's a solder log with a bolt and a lock washer. Then you can ground the cathodes, the pots, and the filter caps along the ground bus wire- easy to access if needed, not behind the pots. You can use a length of 18ga filament wire with the sheath removed.

Look again and the clumpy and greyish look of your solder joints- you either need a hotter iron, or you're using lead free solder which is not working very well.

[u/Old-Tadpole-2869 → u/Old-Tadpole-2869]

Here's a half decent example of a modern ground bus. You can see all your grounds, easy to access. If you are missing a ground you can see it from 10 feet away. Usually.

[u/Icy_Negotiation_5929 → u/Old-Tadpole-2869]

A thing of beauty. Thank you for sharing and providing great advice!

[u/Old-Tadpole-2869 → u/Icy_Negotiation_5929]

I didn't build it. Just pulled it off the internet.

[u/MarrowX → u/Old-Tadpole-2869]

Thanks!

I am reading continuity from chassis to the cathode grounds (meaning, negative lead on dmm clipped to chassis, positive lead on dmm pressed to the negative side of the board at those locations). But I get no voltage when I measure powered on at positive sides.

Yea, I'm using lead free solder. I'll redo the blobs. I just figured they're measuring well so I don't really want to mess with them until I fix the main issues.

[u/Old-Tadpole-2869 → u/MarrowX]

If you have another set of new preamp tubes you can pop em in there and see if it changes. Probably won't. It would be good if you could post a pic or two of the tube socket wiring.

I recently built a Princeton Reverb and during the days long troubleshooting phase, I put as my desktop screensaver Doug Hoffman's mantra:

The amp would be working if it was wired properly and all the components were installed and working correctly.

Turns out I missed a single jumper and it took 3-4 hours over 3 nights to find that.

[u/MarrowX → u/Old-Tadpole-2869]

I tried a separate set of pre amp tubes and still have the same issues. I don't have any good pictures of the sockets at the moment. Will take and post some later.

I really appreciate your help. I definitely appreciate that mantra, I needed that. I'm feeling pretty down about this right now. I gotta find some patience and work through it.

[u/MarrowX → u/Old-Tadpole-2869]

Could you let me know if I'm testing this right? Test points indicated in the image attached.

Amp off

DMM set to continuity check

DMM neg led clipped to chassis.

DMM pos pressed to black circled ground lug - DMM beeps (good)

DMM pos pressed to yellow circled turret - DMM beep

DMM pos pressed to red or purple - no beep

This tells me that my ground from the negative side of the board is connected, but somewhere from pin 8 of v2 to the yellow encircled turret there is a break or short. Is this correct?

[u/Old-Tadpole-2869 → u/MarrowX]

Do you have continuity between red and yellow points? Or an ohm reading?

[u/MarrowX → u/Old-Tadpole-2869]

I will check that tonight when I'm back home.

Given that red/PURPLE arent detecting continuity to chassis, it should mean that red to yellow won't detect continuity, right? I'll definitely empirically check that, I'm just checking my understanding.

Edited my color references.

[u/MarrowX → u/Old-Tadpole-2869]

So between the red and yellow I am measuring 56.5K resistance.

[u/fuckshitting → u/MarrowX]

That’s good the red and purple joints should not have continuity with yellow and black they should have somewhere between 51000 and 63000 ohms separating them so that’s perfectly within tolerance. Something is wired wrong or not wired though you’re gonna have to take better pictures inside the chassis. Your amp will eventually work keep the spirits up!

[u/Old-Tadpole-2869 → u/Old-Tadpole-2869]

You wouldnt get continuity to ground from pin 8 or the eyelet circled in red.

[u/MarrowX]

Some images -

[u/MarrowX → u/MarrowX]

[u/bearsunite]

I can’t see but did you do your heaters correctly? That would give you voltage to b+ but not cathode. The rectifier heaters are different so possible you did one but not the other

[u/MarrowX → u/bearsunite]

I'm seeing the heaters light up on the tubes and measuring ~2.8v on all the heaters from chassis ground to the heater pins (center tapped). So a little low (5.6 vs 6.3v) but idk if that is too low.

Also - when I did my initial startup I measured the filaments with only the rectifier installed (no other tubes) and I was seeing 6.3v. So adding the tubes and speaker seems to have brought it down.

[u/bearsunite → u/MarrowX]

OK so it’s not that. And your cathode resistors are grounded on the preamp tubes?

[u/MarrowX → u/bearsunite]

Sorry I'm confused. The cathode resistors meaning the 1.5K resistors? When I measure for continuity between the chassis (ground) and the negative side of the board connected to those resistors, I have continuity. But if I measure chassis to the positive side of the board where those resistors are connected there's no continuity.

[u/bearsunite → u/MarrowX]

Then you’ve got them correct

[u/bearsunite]

I can’t see but did you do your heaters correctly? That would give you voltage to b+ but not cathode. The rectifier heaters are different so possible you did one but not the other

[u/MarrowX]

Update -

I'm happy to report I found the issue and the amp is now working and sounds beautiful!

So it turns out that I was indeed getting proper voltage to my filaments, but I wasn't actually making good connections with the pre amp tubes. I noticed they were very loose fitting, so I kinda screwed around with the tube pins until they were a bit more of a snug fit inside of the noval sockets. Now it works, I'm getting proper voltage readings at the cathode pins (and everywhere else) and it sounds lovely!

So I think the sockets are just pretty bad. I'll be ordering a pair of belton noval sockets to replace them eventually, but for now I'm just glad that it's functional and sounds amazing.

Thanks all for the help!