Fender 5F1 Champ clone running 4.5V on heaters

BoomTexan

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First off, I'm not entirely even sure if this is a 5F1 Champ. I'm saying it is because it has a 5Y3, 6V6, and 12AX7 setup, but whoever built this godforsaken monstrosity quadrupled the capacitance on the filter caps (and left the voltages within 10V of max on the caps), made a really haphazard eyelet board with bus wires that are about 1mm from shorting on other bus wires, and has the worst cable management I've ever seen.

I paid $60 for this in broken condition and I think that was too much.

Anyways, I got it working, after testing all voltages on the tubes and making sure that there wasn't any outstanding voltages that could kill it. However, the heater current was running 4.5V on all tubes. The rectifier tube wasn't working properly, and it was showing about 1/2 the voltage that it should've been on the capacitors. So, I swapped in a solid state rectifier and the voltages to plates and grid are fine now, but the heater current is still 4.5V. I plugged my guitar in and the sound is really low and incredibly distorted (again, I suspect heaters). Also, there's a really high pitched buzzing when I turn the volume knob down to 0, leading me to think that it's shorting or something. What's also weird is that the voltages on the filter caps seem to vary randomly. Last time I turned it on it was 305V, but the time before that was 440V, and the time before that it was sitting at 200V.

So, what is the best course of action now? Start from scratch? Get a new eyelet board and redo wiring? Get a new transformer and slot it in?
 
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vampwizzard

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are you measuring them correctly? (pin to ground) and did they wire them in series or parallel? The original had series wired heaters.
 

andrewRneumann

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Pull the tubes and measure the heater voltage (Vac) coming right out of the transformer from one lead to another. Maybe the transformer is bad.

As for the varying voltage reading... possibly the circuit isn't grounded properly. Let's see some gut shots and try to figure out the grounding on this beast.
 

andrewRneumann

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As a quick check of grounding, you can measure resistance from each power supply cap negative end to the HT center-tap. Should be 0. Then measure the resistance from each tube cathode to HT center-tap. Should read the value of the cathode bias resistor.
 

BoomTexan

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Pull the tubes and measure the heater voltage (Vac) coming right out of the transformer from one lead to another. Maybe the transformer is bad.

As for the varying voltage reading... possibly the circuit isn't grounded properly. Let's see some gut shots and try to figure out the grounding on this beast.
I did that, and it was still reading really low voltages on the heaters.

I just decided to pull the board to test the transformer and make a new fiberboard and rewire the board entirely, because I kid you not, the chassis ground bus wire was about 1/8th of an inch off the 300V hot wire running through the filter caps. There was all sorts of idiocy and stuff that could get someone killed easily, and I just didn't even want to touch that board, even if I could get the transformer to work.

Still testing the transformer, it's a Blues Jr PT, which obviously doesn't have a heater tap for 5V, which is what the rectifier needs, so the person just branched off the leads and attached a resistor to the heater for the rectifier to bring it down, but I don't want to do that at all, so I think I'll get an EZ81 and just wire it that way. The heater voltages can definitely handle it, it's good for 2.2A, and I only need like 1.75.
 

andrewRneumann

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I did that, and it was still reading really low voltages on the heaters.

I just decided to pull the board to test the transformer and make a new fiberboard and rewire the board entirely, because I kid you not, the chassis ground bus wire was about 1/8th of an inch off the 300V hot wire running through the filter caps. There was all sorts of idiocy and stuff that could get someone killed easily, and I just didn't even want to touch that board, even if I could get the transformer to work.

Still testing the transformer, it's a Blues Jr PT, which obviously doesn't have a heater tap for 5V, which is what the rectifier needs, so the person just branched off the leads and attached a resistor to the heater for the rectifier to bring it down, but I don't want to do that at all, so I think I'll get an EZ81 and just wire it that way. The heater voltages can definitely handle it, it's good for 2.2A, and I only need like 1.75.

Let me get this straight… the PT didn’t have a 5V winding, so there was a dropping resistor on the 6.3V to heat a 5Y3? So all the heaters were elevated by HT? That must have been hard on the tubes and probably hummed like crazy because you couldn’t ground the 6.3V winding. What a mess.
 

BoomTexan

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Yep. Well, he didn't bring all the tubes down to 5V, there was a triple branch wire and the one going to heater of rec tube had that resistor.

I'm gonna either get an EZ81 and keep the 6.3V heater to that pin or put in a SS rectifier slot in replacement and cut heater voltage to those pins.

I've heard of people building kits that have problems with improper wiring and reverse polarity caps all the time, but I've never heard of anyone who messed up a power transformer like this before. The scariest thing about this to me is that the builder knew what he was doing enough to get parts and build from scratch, but not enough to know basic power supply and building technique.
 




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