5e3 (new build) with low filament voltage and low sound

polloelastico

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I have a new 5E3 build using a Soursound PT and OT (diagrams attached) and I'm only getting 3v at the pilot light and filaments. I went through the startup procedure on https://robrobinette.com/Tube_Amp_Startup.htm and that was the only thing that never checked out (at the time, I assumed it was because of the light bulb limiter I was using so I didn't think much of it).

However, once I plugged into 120v directly it works, but it's super quiet. I'm pretty new to this and I'm not sure where to start as far as measurements go. Am I wrong to assume that I should be getting 6.3v out of the green PT wires?

Thanks
 

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Ten Over

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I have a new 5E3 build using a Soursound PT and OT (diagrams attached) and I'm only getting 3v at the pilot light and filaments. I went through the startup procedure on https://robrobinette.com/Tube_Amp_Startup.htm and that was the only thing that never checked out (I assumed it was because of the light bulb limiter).

It works, but it's super quiet. I'm pretty new to this and I'm not sure where to start as far as measurements go. Am I wrong to that I should be betting 6.3v outs of the green PT wires?

Thanks
Is that GRN wire to chassis or GRN wire to GRN wire?
 

polloelastico

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Hmm, I'm not positive on which green wire you mean, but if you mean the cloth covered one in the cluster of green/yellow, red/yellow and green cloth wires that are grounded the PT bolt -- the green cloth wire runs to the power bus ground on the top left eyelet.

I used the stew-mac diagram exclusively except that I had a PT with a tap for the filament so I grounded that wire to the PT bolt directly (and omitted the resisters and ground wire of the pilot light), and I ran power to the fuse -> switch instead of switch -> fuse (updated since I took the photo)
 

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polloelastico

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It's 3v from the green wire on the pilot light to ground. I measured each filament that way along the chain and they all read the same.
 

polloelastico

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Ok, and then of course if I measure from each green wire on the pilot light to the other, it's around 6ish volts AC, close to 7, which I think make sense since it's just the sum. Maybe that's how it should be measured anyway?

Sounds like I'm barking up the wrong tree with the heater voltages.
 

Ten Over

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Ok, and then of course if I measure from each green wire on the pilot light to the other, it's around 6ish volts AC, close to 7, which I think make sense since it's just the sum. Maybe that's how it should be measured anyway?

Sounds like I'm barking up the wrong tree with the heater voltages.
Yes. You've got it.
 

polloelastico

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I was super excited to hear the subtle speaker hum when I finally had all the tubes in and turned it on, but with a guitar plugged in it's about as a loud as a electric guitar played without an amp. The tubes are all new and look like they are working correctly.
 

D'tar

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Check your V1 plate load resistors. Ensure 100k ohms(brown-black-yellow) and not 100 ohms(brown-black-brown)

1669083569836.png
 
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gabasa

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Kudos for going with Soursound, they make awesome sounding transformers.

I'd say do the easiest things first and triple-check your wiring everywhere.
Check all your ground points for continuity to ground.
Measure all your resistors to make sure they match the schematic.
Make sure all solders are good.
Double-check that your tubes are good by swapping with known good ones.
Measure all your B+ voltages and post them here, assuming you know how to do it safely.
Measure the voltages on all your tube sockets and post them here, assuming you know how to do it safely.
Post detailed pics here.

The community here has helped me with much worse ... you'll get there.
 

polloelastico

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Check your V1 plate load resistors. Ensure 100k ohms(brown-black-yellow) and not 100 ohms(brown-black-brown)

View attachment 1053611

Oh no, those are 100 ohm! I think we have a solution here -- can't wait to swap those out tomorrow. Thanks for spotting that! I verified the grid stoppers but didn't even think of checking the ones on the board.

It's funny, it did go through my head that the V1 tube was running a bit cool. I tried swapping it out, but stopped there and just shrugged it off.
 
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corliss1

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Making a voltage chart would have helped you catch that faster, as you likely would have seen a very small voltage drop across that resistor, or a very high voltage on the plate. Always always always do a voltage check when having any issues.
 




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