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5F1 cathode resistor voltage extremely high
Hello, I don't post here often, but I'm attempting my first build after having a bit more of a formal understanding on how all this stuff works. I'm having an issue with it, and google isn't quite leading me to an answer. It's a 5F1 champ. I gutted a Fender Excelsior amp that I never used, so I'm using the cab and chassis from that and I stuck a bunch of turret boards in it and it is what it is.
The issue I'm having is that the cathode resistor has way too much voltage across it. The Power transformer I'm using is the Ted Weber W022772: https://taweber.powweb.com/store/022772sch.jpg
with the RED/WHT 600V taps the B+ at the 16uF filter cap was about 350 volts, the 6V6 plate had 315V with respect to ground (261 with respect to the cathode), and the cathode resistor (470ohm) had about 55 Volts across it. I have a silverface AA764 champ, and according to that there should only be about 20V across the 470 ohm.
I looked at the Ted Weber 5F1 schematic, and he used the RED 660V taps. I figured with higher voltages from there, a higher voltage on the plate would result, leading to higher plate current, thus a higher plate "resistance" and larger drop to the cathode, and the voltages would level off. That wasn't the case
Currently I'm measuring 384V at the 16uF filter cap, 332V on the 6V6 plate (272 with respect to the cathode), about 280V on the screen grid, and 59V across the 470ohm (measured at 452ohms), as opposed to the 20 I'm looking for.
I also noticed that on the AA764 schematic, since the 5F1 doesn't say anything about voltages, Fender only expected to drop 10V across the output transformer primary winding, I'm losing about 50V there. I'm not sure that has anything to do with it, but I thought it was unusual.
Anyone have any idea what's going on here?
Oh yeah. . . I'm not finished with the build either, I was just checking to see that everything was normal as I'm going along. By not finished I mean Only the filter caps and power tube and Power/Output Transformers are connected, and the tubes are plugged in. The preamp stages aren't linked in yet, as in the 6V6 control grid has nothing connected to it yet. Does this matter for the bias resistor? The OT is a weber W022905M, and the only deviation from the original schematic so far is that I have a switch between 4 and 8 ohm outputs.
The issue I'm having is that the cathode resistor has way too much voltage across it. The Power transformer I'm using is the Ted Weber W022772: https://taweber.powweb.com/store/022772sch.jpg
with the RED/WHT 600V taps the B+ at the 16uF filter cap was about 350 volts, the 6V6 plate had 315V with respect to ground (261 with respect to the cathode), and the cathode resistor (470ohm) had about 55 Volts across it. I have a silverface AA764 champ, and according to that there should only be about 20V across the 470 ohm.
I looked at the Ted Weber 5F1 schematic, and he used the RED 660V taps. I figured with higher voltages from there, a higher voltage on the plate would result, leading to higher plate current, thus a higher plate "resistance" and larger drop to the cathode, and the voltages would level off. That wasn't the case
Currently I'm measuring 384V at the 16uF filter cap, 332V on the 6V6 plate (272 with respect to the cathode), about 280V on the screen grid, and 59V across the 470ohm (measured at 452ohms), as opposed to the 20 I'm looking for.
I also noticed that on the AA764 schematic, since the 5F1 doesn't say anything about voltages, Fender only expected to drop 10V across the output transformer primary winding, I'm losing about 50V there. I'm not sure that has anything to do with it, but I thought it was unusual.
Anyone have any idea what's going on here?
Oh yeah. . . I'm not finished with the build either, I was just checking to see that everything was normal as I'm going along. By not finished I mean Only the filter caps and power tube and Power/Output Transformers are connected, and the tubes are plugged in. The preamp stages aren't linked in yet, as in the 6V6 control grid has nothing connected to it yet. Does this matter for the bias resistor? The OT is a weber W022905M, and the only deviation from the original schematic so far is that I have a switch between 4 and 8 ohm outputs.
Stuck another in there, measured 27 volts across it. Kinda high, but not absurd, it's expected when there's 430 volts coming off the rectifier, but that thing is another story. . . I'll report back when I finish making those connections, much thanks.
It doesn't happen until the 12AX7 goes in, which means it gotta have something to do with what's going onto the grid, pin 5, of the 6V6 from the pin 6 plate of the 12AX7. It has to be something simple I'm just overlooking...
I'm gonna take fresh look at it tomorrow
Oops. Now rather than pulses it squeals unless the volume is down. The layout says the blue wire goes to pin 3 on the 6V6 and the red goes to the B+ at the first filter cap, which is how I have it. A quick google search shows reversing these might help, but then it will be backwards according to the diagram, I guess that's an okay thing as long as it works? I'm going to find out in a few minutes, just thought I'd mention it. . .
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