That makes sense. I knew that something like this was happening, just didn't know exactly what and how.
I wasn't going to post all this here because it does get off topic but I guess in a way it still deals with the power supply and it's voltages. If a Mod feels this should be moved, please do so to the appropriate section. As you will see this design calls for one test point for each pair of power tubes. I ground the volt meter to the chassis and connect the volt meter's positive to this single test point. In most schematics that I've seen there are three test points for each pair of tubes: a single ground a two positive (one for each tube) grounded to the negative test point with a 1ohm resistor. I know the 15ohm that this circuit calls for changes the reading and that it then will have to be divided by two to get a reading for each tube but, something is not right. I'm getting 2.30V for the left channel and .47mV for the right channel. No matter which direction I turn the bias pots, a small change occurs and then the readings continue to go up. Of course, I've read ten different articles on biasing tubes and everyone has their own opinion on doing it. Some say you should NEVER use a volt meter and that you need a special biasing tool (which I'd love to get, but my budget won't allow so at this moment). Do I have the power on while checking bias, and do I have the amp playing music? Some article I read said to leave the amp in standby, but then theres no negative voltage flowing just the heater supply. The resistor's read fine and check out as 15ohms exactly on the Volt Meter so, there must be a bad connection somewhere. Any advice is appreciated, but here's what I was going to do to remedy this situation, tell me if I'm way off basis here: I am going to replace the test points and add one on each channel so all four power tubes have their own test point.. Then, I want to change the resistors out to a 1ohm resistor as I've seen in so many other schematics. Is it fine to ground the volt meter to the chassis still or should i install a ground test point? Honestly, I would rather check bias from inside the amp anyways so I usually just ground teh volt meter to the signal ground bus since it's in a central location and theirs nothing positive or hot nearby for it to slip off and touch while also being grounded. Or is this whole bias test point wiring fine, and I just need to check connections and maybe replace the 15ohm resistors with some new ones?
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Using ohm's law, 2.3V/15R gives 150mA, a bit excessive to 6V6 in pentode mode, not sure for triode.
In the other side, .47v (I suppose, .47mv is nothing), 30mA appears to be too low. Perhaps a deep review of the state of passive and active components in the stage will give a way to start pesquise.
Just wante to let you know that the problem has been solved. I changed out the bias pots as they were linear type and went with audio type for a consistent change in both directions. I then swapped the 15R resistors with 1R, I did not add any additional test points, I left one on each pair of 6V6s. Overheating at idle was still occuring. I took a break and when I came back I started to really study the circuitry and the path of the negative voltage, using a volt meter I checked each connection from the negative power supply to the tubes. This is where I discovered that the negative voltage was running through my coupling caps! It should actually enter the line into the tubes AFTER the coupling caps. When I pulle up the schematic this is how it's drawn as well...not sure why or how I did that but I did. I went ahead and swapped in new coupling caps since I had some Mudorf Silver/Oil Supremes come in the other day, and I moved the wiring around to where the circuit flows correctly.
I pulled up the "How to Bias" article at the ducanamps website and typed up a version of how to bias a tube amp with the appropriate specs for the 6V6GT's that I am running. Then I biased the amp successfully for the first time. According to my calculations I am getting 9.97Watts from each channel! Not bad for this Amp. Starting my build of AudioTropic's Moebius Line Stage using four 6T4s to place before this 6V6 Musical Machine tomorrow. I'm sure I will have a couple questions along the way so be on the look out for any posts I make! Thanks again for everything DIYAudio!
Well, congratulations. But, once again. I'll give some suggestions from my own experience:
1) When testing any electric device, it is of good practice to have a series lamp (Tungsten, incandescent) in series to the power cord. This way, any mistake in the wiring, or defective component, the lamp will glow, indicating the trouble is present, and limiting the current available to the faulty device. I do it from secondary school, a professor called Todoruck suggested me it and I never stop obey him.
2) Don't worry about cap trades and types. the only true value of them is that they have the right value, good isolation, low leakage and small in size. The "auido grade" normally are the worst option.
1) When testing any electric device, it is of good practice to have a series lamp (Tungsten, incandescent) in series to the power cord. This way, any mistake in the wiring, or defective component, the lamp will glow, indicating the trouble is present, and limiting the current available to the faulty device. I do it from secondary school, a professor called Todoruck suggested me it and I never stop obey him.
2) Don't worry about cap trades and types. the only true value of them is that they have the right value, good isolation, low leakage and small in size. The "auido grade" normally are the worst option.
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