Build Your Own Clone Message Board

Hello! First time builder here and starting with a jtm45 kit. Ive got everything in and now going through the fun of troubleshooting.

Im on step 9 of the firing up instructions. The main flips on and the indicator light works. I then powered off and dropped in the gz34 tube. Flip it back on and it glows. Two questions.

First, the instructions say pull a voltage off the 32uf 32uf capacitor red terminal. I dont get anything in standby. Looking at the schematic that makes sense to me. I can pull a voltage off the tube and get 380v which is low of the 450 in the instructions.

Second, i regrettably turned the standby on and smoked the 1kohm 1w resistor. I pulled all the voltages in step 9 and they all read low. Do you have any thoughts on what could be happening here?

Im going to triple check the circuit with some fresh eyes in the next couple days but appreciate any and all help from the amp gurus!

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Sorry correction im smoking the the 10kohm 1w resistor next to the 16uf capacitor

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double check the 16uf cap. it appears its installed backwards.... good luck !!

just take your time,,, I made a couple minor mistakes building mine,,, I did catch the errors when double/triple checking my work.... it happens …. the instructions are fantastic with these BYOC kits !! but still its possible to misinterpret some of the verbiage at times,,, I love my JTM. I just finished mine a few weeks ago,,, I have been gigging with it,,,i posted some pics,, I did add a master volume and a metropolis FX loop which works fantastic with this amp... Cheers !

Oooo good call! Thinking back i wasnt looking at direction of the turret mpunted caps. For the small yellow ones, is there a direction and does it matter or is it just the bigger caps?

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It's the type of cap that requires a certain polarity. It ain't the size,,, they normally will have arrows on them and or one end will have an indentation...

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For the board-mounted caps, it's just the four black electrolytic caps where the polarity matters. From what I can see on the photo you posted, it's just the 16μf cap in the middle of the board that's mounted backwards. But double-check your build against the layout diagram in the instructions to confirm the proper orientation of all four.

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“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Alright when through the 120v layout all looks good now. When i pull rectifier tube voltage on standby i get 350v, still low. Kicking off standby im not smoking the resistor so progress! Now the issue is i pull voltages across the caps and i consistently get 520 volts sounds like all the terminals are somehow connected but I'm not seeing that anywhere.

Ive checked the turret board to make sure i have underboard wiring right, components right and checked turrets against ground to make sure I'm not shorting anything. Any thoughts? Again no power tubes, i did roll the impedance over to 8 ohm and plugged a speaker in (no noise out of speaker as expected).

Whats the next thing to check for trouble shooting? I know the rectifier tube isnt the best as i pulled from a combo amp that was microphonic but it was working fine aside from microphonics.

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I would go from the beginning through each step and double check every single thing... look at it as if you were building it again..... not only that the right components are in the proper place but every single solder joint.... these amp designs are very simple but are very unforgiving when things are not correct...…… REMEMBER if you get frustrated just take a break..... especially if you are going through the power up process.... I would highly suggest that for now you use the tubes are new especially that they are the correct ones... especially the power tubes that are a paired set. perhaps once you get it all working and properly biased than maybe change up tubes and whatnot... again,,, be safe !!!

Thanks for the advice, ill take a break and step back a few days! I'll get a new tube and try it out and see if it changes things. I did end up checking the power tansformer line voltages to make sure i got the heaters right and the yellow / red voltages (checked against valvestorms kit values). One thing i just want to make sure im setting right in the initial phases is thr trim bias pot. I would think youd want it cold in initial startup then bias up to voltage. Dumb question for sure, what way do you turn it, clockwise or counter clockwise?

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Clockwise to increase voltage. It's very touchy so turn slowly.....

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Alright guys getting some progress (maybe in the wrong direction) but ive gone through and checked all the wiring including making sure my solders were ok with my multimeter going across various components.

I pulled up the valve storm jtm45 instructions and the firing up procedure to try and check a few other things. One of the things to check is pin 5 of v4 and v5 (plate voltage i think). They say it should read -45v...im reading -220v. Im thinking i might have fried my trim bias pot. I read 50k across the two terminals on the same side, but getting an open connection across the opposite terminals. Thats not right correct? What should that be reading? I imagine there should be some degree of resistance here which i think may be a cause for my high voltages (also blowing the fuse anytime i switch off standby).

Secondary question, i saw there is an updated wiring schematic which im checking against rev 1 of the dwg. Is the one on the forum rev 1 dated 7/16/15 the latest?

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Dropped a 10k resistor in parallel of the trim bias pot and the voltages dropped dramatically on the v4 v5 pin 5...pretty sure i fried the trim bias pot with too much heat..oops! Anyone got a part number for a replacement?

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Are you sure? They're pretty tough. Have you tested resistance across it at both ends of its sweep to see if it's functional? Do that with the voltage OFF.

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

I think so, just took a resistance across the connected terminals and got an open connection. Turned fully and still read open. I had a tough time soldering that one and buttered it up pretty good so some solder got up near the plastic especially on the the side with the resistor. The other end reads the expected 50k but i cant get anything across the others. Doing the 10k jumper across made the pin 5 voltages make more sense so I'm going to replace it just not really sure what to order.

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Are you reading AC voltage instead of DC?

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

Morgan - nope i was measuring dc. Came up with 220v, dropped in a resistor to bridge around the trim pot and it came down to -48v.

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hope you get it all figured out! I think you are close! when I solder I always take steps to minimize the heat to the component. on things with short leads like that board pot I clean the leads, and tin . and on longer leads I put a alligator clip to help dissipate the heat.... also I have made it a habit to test each component prior to installing .. sure these things take extra time but it will pay back when I am finished.... good luck !

Alrighty guys! I ended up troubleshooting it with a local amp guru and we found a few suspect caps and threw in some preamp tubes to take some of the current spike. Now that said, got it fired up and it sounds great! One issue or non issue that I'm looking for help on. I was using this jj gz34 rectifier tube during all of this. Now when i keep it off standby i see some internal sparks. Ive changed it for the older tube i had laying around (ruby 5ar4) and no sparks. Looking at other forum jj's get some mixed rep. Any one have bad experience with jj's? Should i just watch the tubes when pulling off standby and if i start seeing issues, go back inside the amp for more trouble shooting?

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No. Don’t use the tube that sparks. It’s not good.

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

Assuming that it was new, the seller of that JJ rectifier should replace it for you at no charge..

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Well...that cap that was initially installed backwards resulting in the cooked power supply resistor could have easily caused some damage to the rectifier. It may not have been bad when it was new.

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

Fair point. Forgot about that....

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2