JTM1 DIY Build stays silent

[Kenny1547]

Hey Guys!

First post here, just been lurking for a week or two. Thing is, ive been wanting to learn some new Stuff and have a new DIY Project, so ive been trying to learn some electronics and build myself an amp. Im done now, but it just wouldnt make a Sound. Ive errorchecked against Matecs schematic (Big shoutout to him and the JTM1 thread, i couldnt have done anything without that) and a layout from him several times and fixed some stuff, but now it still doesnt work.

My question is if someone with a little more experience in electronics and amp building can look over my layout and schematics that i used to see if they find an obvious mistake? Im kinda at a loss here! That would me great

I used Matecs JTM1 Schematic and a Layout i found from him that i tried to convert back to the normal Tone knob Tonestack and will attach those. My Voltages are a little higher too, my Secondary gives of 190V instead of 180V and the rest ist higher acordingly. The Tubes all seem to heat up and glow etc, and when trying to measure voltages at the 3 big caps theres a slight sound at the speaker, so maybe something at the input is wrong?

Greetings,
Till

[Kenny1547]

Ive also tried injecting a signal and if its loud enough (tried it with a headphone amp) it does amplify stuff, doesnt really matter where i inject, even at the input and all tube grids, just has to be at like half volume of the headphone amp. Any ideas?

[pompeiisneaks]

If you're working off a known good layout/schematic, and modify it, it's best to revert to the known design, and make sure that works. If it does, try the mod again, but make sure you write up a schematic and illustrate the mod so that someone can double check the attempted mod.

Also pictures of your real amp will help people see if something seems off. (legible ones, get it in a bright room, take several from the top down, angled into the pots, the output wiring etc.)

~Phil

[Tony Bones]

You can inject a signal into the input, then measure the AC voltage at various points in the amp.

Start by measuring the AC signal between grid and ground of V1a, V1b, and V2a. Then measure between grids of the output tubes. For the last one, put one probe of your DMM on each grid. Again, set the DMM to measure AC volts.

[Kenny1547]

If you're working off a known good layout/schematic, and modify it, it's best to revert to the known design, and make sure that works. If it does, try the mod again, but make sure you write up a schematic and illustrate the mod so that someone can double check the attempted mod.

Also pictures of your real amp will help people see if something seems off. (legible ones, get it in a bright room, take several from the top down, angled into the pots, the output wiring etc.)

~Phil

Thanks!
Well, its a known/good schematic as far as that some people definately seem to have build this amp, but all have modified the tone stack etc. I seem to be the only one to have tried to closely follow the real (well, the schematic that Matec posted, wich is exactly what i linked in the first post, its just my more or less own layout with the 1 tone knob tonestack ) schematic with the normal tonestack ( just one tone knob ), since this is my first time really dealing in electronics and im not really capable of modifying anything yet

You can inject a signal into the input, then measure the AC voltage at various points in the amp.

Start by measuring the AC signal between grid and ground of V1a, V1b, and V2a. Then measure between grids of the output tubes. For the last one, put one probe of your DMM on each grid. Again, set the DMM to measure AC volts.

Hey, thanks for that tip!
V1a grid voltage is pretty much not there ( i think thats right though? ) and gets to 4v AC at V1b, V2a grid sits at 0,1V, V2b cycles quite fast between 35V, 5V and 0,2 or something like that, that seems strange, is that where that problem seems to be? Between the output tube (its just one 12AU7) grids is 0,075V

[pompeiisneaks]

Hey, thanks for that tip!
V1a grid voltage is pretty much not there ( i think thats right though? ) and gets to 4v AC at V1b, V2a grid sits at 0,1V, V2b cycles quite fast between 35V, 5V and 0,2 or something like that, that seems strange, is that where that problem seems to be? Between the output tube (its just one 12AU7) grids is 0,075V

The fact that you have 4VAC at v1b and then nothing really at v2a, means that you're losing the signal somewhere after V1b and the tone pot into V2a. I'd try stepping backwards through the chain to see where that may be.

Try checking VAC at the top of the tone pot, see if somehow that's not working right, then jump back another step to the other side of C102, etc, and somewhere there you 'should' see the signal. If it's not even there past the output at the other side of C15, then you may be losing the AC at that tube, i.e. it's not conducting. I.e. you've gotten that signal into V1a, and at V1b the input is 4VAC, then it should be jumping up again at it's output.

~Phil

[Kenny1547]

Thanks so much for helping, i seem to have found the problem, i think. C15 does normaly carry the signal to C104 with ~4VAC but over C104 it goes down to 0,5VAC, that probably shouldnt be the case right? Ive tried resoldering it and checked it with the DMM unsoldered and it showed up normally, can it be defective nevertheless?

Edit: Checked the resistance of the cap and it sits at 4,8 mohm without change, i read that that means it IS bad and i have to get a new one?

I changed that cap and now i get up to 20Vac to the tone pot depending on where it sits, but the connection to V2a just stays at 0,35Vac

Edit2: Okayyyy so, my R101 should be 100k Ohm and ive only bought 100k ohms, but it is 10k, looks exactly like all 7 others, just is a different Ohm value apparently?? We'll see if it works after i switch it...

[pompeiisneaks]

Good to hear you've localized the problem, crossing fingers that you get it!

~Phil

[Tony Bones]

Glad to hear that you're getting there. You're learning how to troubleshoot!

[Kenny1547]

Glad to hear that you're getting there. You're learning how to troubleshoot!

Good to hear you've localized the problem, crossing fingers that you get it!

~Phil

Thanks guys! Mightve been a little bit of a hard first amp build, but hey, im learning tons of stuff so thats cool!