Valvestorm JTM45 First Build Help

[Oddteaon]

I tested on V4 and got -48V

[Stevem]

That’s plenty of bias voltage to keep the tubes in check .
I would have to guess that there are two possibilities now.
Either you have a wiring issue with the output tube sockets or you have a shorted output tube.

[Oddteaon]

I tried to improve the solder and connections of the capacitors and resistors going into V4 and V5 and then re-tried to bias while measuring mV on pins 5. The values were jumpy, and my hand was pretty unstable. I managed to get both to be around 42mV, plugged my guitar in, and played, and it sounded fine. Then I connected it to my PS2A so I could check it under larger volumes, and the speaker started making noises, and a fuse blew.

I think I'll re-solder the turret board, but apart from that, what else can I try?

[Stevem]

On pin 5 you should not be reading millivolts like you keep reporting back with unless there is a bias checking resistor.

Does this kit/ build have a 1 ohm resistor going from pin 8 of the output tube sockets to ground?

[johnnyreece]

Thanks, I'll give it a try.

I used the fast blow 2A 250V fuses that came with the kit as the wall AC here is ~230V.

Silly thought, but are fast-blow fuses used for mains in Europe? Over here (at least in all my builds) the mains fuse is a slow-blow. Not sure if this is an issue or not, but just something that jumped out at me.

Also, are you seeing any evidence of arcing? Definitely want to clean that up, if it's visible.

[Oddteaon]

I meant to say I was measuring on pin 8. Yes, we have a 1ohm resistor from pin 8 to pin 1, and the extra leads from pin 1 are connected to ground.
My wiring was a mess and I suspect that it may cause parasitic oscillation, so I shortened long wires and separated them as in the guide. Re-wired and the HT fuse blew after I saw a spark. The HT fuse is also a fast blo.
Perhaps I should use a slow blo, but the kit came with fast blows.

[johnnyreece]

On my builds, mains fuse is slow blow; HT is fast blow. Others may disagree, but that's what works for me. Interesting that the HT fuse blew, though. That's a new issue, right? Have you thought of investing in a light bulb limiter? Fuses aren't really expensive, but that cost *does* add up after a while.

[Stevem]

Pins 8 and 1 should be jumped and then the 1 ohm resistor goes between 8 and ground.

Is that how you have it wired?

[Oddteaon]

I can't find a light bulb limiter, where I live.
I've connected the resistor between pins 1 and 8 and then to the ground via pin 1 as shown in the instructions.
I am not sure that the HT fuse blowing is new actually. It did happen once before when the output leads were reversed.
As everything is new (including the output tubes), I suspect that the problem is probably bad soldering somewhere and not faulty components.

[Stevem]

In terms of blowing fuses it's kind of unlikely that poor solder connection will cause that unless it's making for a loss of bias voltage to pin 5 of the outputs.

[johnnyreece]

Re-wired and the HT fuse blew after I saw a spark.

This seems like a pretty big concern...where did the spark come from?

[Oddteaon]

The HT fuse, one of the connections.

[Oddteaon]

Update:
I examined all connections and re-soldered any connection that seemed fishy. I just tried it again, and it worked! No oscillation and I managed to bias and play.
I was super excited and connected the amp to the Fayette power station 2A so I could test it with higher volumes (I can't just use it with a speaker cabinet directly as I live in an apartment).
Once I tried to use it via the PS2A the main fuse blew (after everything was perfect). I don't know why it would cause this to happen. also, when the HT fuse blew it was when I tested it via the PS2A and not directly with a speaker cab.

Anyway, sadly, the amp doesn't work anymore, and the voltages on pin 1 of the preamps are very low now. I don't see any visible damage to the tubes or any other component. What could have happened? Why is it happening with the PS2A?

[Stevem]

I am sorry to inform you that you can only blow a fuse so many times before the excessive loading on the power transformer takes its toll.
This is why you should have built a light bulb limiter to use even before you ever powered the amp up.

Now a would refer you to near the top of this tech section to read the sticky on blowing fuses / debugging and read up on tracking down why you might have your issue .

Be prepared for buying a new power transformer possibly.

[Oddteaon]

Thanks, I’ll do that.