First post, my “new” 18W

[Skydog6653]

Question, guys; when I first power up the amp, the V4 EL84 glows brightly for an instant, then dims down to match the other (V5 EL84) power tube. Is this normal, or is it indicative of an issue. The tube in question is a new JJ.

[JMPGuitars]

Question, guys; when I first power up the amp, the V4 EL84 glows brightly for an instant, then dims down to match the other (V5 EL84) power tube. Is this normal, or is it indicative of an issue. The tube in question is a new JJ.

It's not normal at all, and it's a fault in different batches of JJ tubes. I don't recommend JJ EL84 tubes at all. I posted this video 6 years ago: https://www.youtube.com/watch?v=21G6TkukwY8

Obviously they've still got issues if your tube is new.

Thanks,
Josh

EDIT: I use new issue Tungsol, Mullard, or TAD for EL84s.

[crgfrench]

Simple test to see if it's the tube or the circuit: swap tubes in sockets 4 & 5 and see what happens

[Skydog6653]

Problem moved to socket 5, so it's the tube; JMP, it behaves just like the one in your video.

[JMPGuitars]

Problem moved to socket 5, so it's the tube; JMP, it behaves just like the one in your video.

Return the set if you can and get a different brand.

[Skydog6653]

Problem moved to socket 5, so it's the tube; JMP, it behaves just like the one in your video.

Return the set if you can and get a different brand.

Waiting to hear back. I might have to settle for replacement JJ’s. Weird though, they acted like my issue was a fluke!

[JMPGuitars]

lol, reply to them with a link to my video. Let them know that I went through around 10 sets with the same flaw.

[crgfrench]

Is it just my browser, or are the emojis amplified on 18watt.com?

[crgfrench]

I posted this video 6 years ago: https://www.youtube.com/watch?v=21G6TkukwY8

In that video the rectifier tube does the same thing, to a lesser extent.

[JMPGuitars]

In that video the rectifier tube does the same thing, to a lesser extent.

To a significantly lesser extent. In the rectifier there's a tiny burst of orange light at the base of the tube, which then heats the tube and operates normally. It's not anything like the light bulb effect the EL84 has. But if it makes you feel better they're all JJ tubes. Compare it to your tubes and rectifier and see what they look like.

BTW- look closely at the bottom of the heaters and see the way they behave. The defective EL84 is burning hotter than any of the other tubes throughout the whole video. It's a shared cathode bias with matched tubes; there shouldn't be any significant difference if the tubes are both good.

[Skydog6653]

Phase 9! I've ordered the remaining resistors & capacitors for replacement. However, my primary goal is to resolve this grounding issue. I ordered the 12 ga bare bus and 22 ga black stranded wire. The following pictures are of the current ground “system”. I have a few questions if someone would be kind to answer. How many “sub-grounds” should I have? IDK if that's a correct term, so I guess I want to know how many solder lug to chassis' to have? You guys all mention to separate the power and pre-amp sections. My big question, then, is what components are in each “sub-ground” if you will?

5F055D85-3B69-448F-BEB3-63CCAC282A51.jpeg

0421246E-CD79-4978-A46D-1405C23EE0A7.jpeg

[crgfrench]

The layouts in the downloads section show the specifics of grounding. For example, in the Classic Marshall 18W section, "Richie's Later Corrections Layout" shows 3 ground points (the AC ground, poweramp ground and preamp ground ) and every component's ground connection to them.

[Skydog6653]

Unless I'm reading that layout wrong, the bias ground from the power section goes to the same ground as the pots.

[geoff 1965]

hello skydog,
the valvestorm layout you posted look's good,it's one of the latest "2018" and the layout is virtually the same as yours.richie hall and mark huss have put a lot of input into this forum and i'm sure if there were grounding issue's they will have sorted them.
keep us posted with your progress and updated pics.

18watt_TMB_Layout.pdf

[JMPGuitars]

Unless I'm reading that layout wrong, the bias ground from the power section goes to the same ground as the pots.

You're correct. Those layouts are based on the original 18w, and do not necessarily include modern improvements to ground schemes. I don't recommend following the ground scheme from that layout.

Thanks,
Josh

[Skydog6653]

On the TMB circuit shown, (Valvestorm) why aren't the treble and bass pots grounded? download/file.php?id=11528

[geoff 1965]

that's how all the TMB tonestacks are wired,notice your treble & bass pots are wired the same except you don't have the master volume.how's things going with the amp?

[JMPGuitars]

On the TMB circuit shown, (Valvestorm) why aren't the treble and bass pots grounded? download/file.php?id=11528

A better question is why would they be grounded? Always look to a schematic for more details (never rely only on a layout): storage/18watt_tmb_JAschematic.pdf

Every part has a function within a circuit. Find the tone circuit you're talking talking about on the schematic, and see if it makes more sense from the schematic perspective.

[Skydog6653]

Your question is a valid one, but beyond my ability to answer. I was studying the layout and noticed that some, not all, of the pots are grounded. I was curious as to whether it was an oversight or not. I replaced the 2/1M resistors on the input jacks and the 100KR on the V-T normal and the 82K on the TMB side. Also, the 1K5R/25uf cap. I ran the 12 awg square bus wire for the new ground and tied everything from the pots etc. into it with the 22awg stranded. I left the ground near the trannies intact. I grounded the power cap etc. to its own ground. After a 10 minute warmup I took the amp off standby and it sounds good. Not great, not yet! It still has a hum, albeit a lot less. The hum is accentuated by the volume. It is slightly more noticeable on the TMB channel. Just how quiet can I reasonably expect this amp to be? Right now I'd say it's giggable, but not recordable or miced, if that helps. I'll take some more pics tomorrow with better light.

[JMPGuitars]

My question was posed for you to learn more about the circuit and improve your schematic reading skills. Pots are variable resistors, that's all. If you can find the part of the tone circuit on the schematic, you can see how those resistors interact with the tone circuit. You can study further and see why only some of them connect to ground.



Remove the PI ground from the preamp ground. Connect that to the power amp ground.

After that if your hum is still annoying, tap things with a chopstick, and try chopsticking wires and see what affects what.

Thanks,
Josh