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I wonder if this is due to variations in the transformer windings or because of the different tubes being used.
I don't know. Maybe it's because of the different tubes, or maybe all of the new resistors?
BTW, I just measured the 6Z4 again for the heck of it. It's now down to 7.03V instead of 7.09V this morning. I'm sure that's probably because there's more draw on the lines now since everybody's awake and using more juice than this morning.
A regulated PS would solve that little problem, right?
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HOTT Modded Xiang Sheng 708B Sennheiser HD600 Sony CDP-397 CD Player FEEDBACK My NEW Website!
All the new resistor values are the same as stock so it couldn't be them.
"BTW, I just measured the 6Z4 again for the heck of it. It's now down to 7.03V instead of 7.09V this morning. I'm sure that's probably because there's more draw on the lines now since everybody's awake and using more juice than this morning."
That would make sense. It would be interesting to record the voltage of the wall socket at a few different times throughout the day to see how much it changes.
"A regulated PS would solve that little problem, right?"
Yeah, but you'd have to get a new transformer with higher voltage heater windings to accommodate the voltage drop of regulators.
"All the new resistor values are the same as stock so it couldn't be them."
Yes, the new resistors are the same values, but they're at much tighter 1% tolerances. If a lot of the stock resistors were well above or below their rating, that could change voltages, correct?
"That would make sense. It would be interesting to record the voltage of the wall socket at a few different times throughout the day to see how much it changes."
With my Panamax MAX1000 in my home theater system, I have seen it's meter range anywhere between 106V all the way up to 129V.
"Yeah, but you'd have to get a new transformer with higher voltage heater windings to accommodate the voltage drop of regulators."
True, and it would probably cost a pretty penny as well. I don't know though. It might be worth it if I decide to go to a new case and all the other things I mentioned before in our PM about wanting to do.
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HOTT Modded Xiang Sheng 708B Sennheiser HD600 Sony CDP-397 CD Player FEEDBACK My NEW Website!
If you replaced all those resistors why not make it an Optimized Morgan Jones Amplifier so it can work with low impedance cans ?
The Optimized Morgan Jones Amplifier uses three 6DJ8/6922 tubes and the 708B has two 6DJ8/6922 and a 6N3, so it's not just a simple matter of swapping resistors unfortunately. Also the 6N3 has a different pinout than the 6DJ8/6922 and a few months back I was considering building an adapter to use one in the 6N3 position along with changing the required resistors, but decided against it. Lately I've been thinking about doing it though since I'm planning on ordering all the resistors very soon anyways. I'm kind of on the fence on doing this mod, but nice 6DJ8/6922 sure are a lot easier to find so I just might do it after all.
So was the high voltage due to the original resistor operating outside its temperature range?
There was no resistor originally. The PS is designed to work off of 110V, but over here in the US, the live voltage is 120V. Since the PS in non-regulated, the voltages throughout the amp are running a little higher than they should be, hence the stock heater voltages running at 7.58V.
The 1Ω - 10W resistor was added to drop the heater voltage down near the nominal operating voltage of the tubes, which is 6.31V.
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HOTT Modded Xiang Sheng 708B Sennheiser HD600 Sony CDP-397 CD Player FEEDBACK My NEW Website!
Here's something I'm kind of thinking about doing as far as a new chassis is concerned. I just whipped it up in AutoCAD 2002. The actual dimentions will probably be something like 17"W x 4"H x 10-12"D. Of course, nothing is written in stone yet.
If I can find them, I'd really like the input selector and volume knob to be solid wood, about 2" diameter. The mini-toggle would be for a defeatable crossfeed circuit. The power button would be one of those nice all-metal ones that has the blue lit ring around them (unless I can get them in a different color). The 3 LEDs for the input selector and crossfeed switch would be those small orange ones that came in the 708B window unit. The entire chassis would be aluminum with a dual layered front panel. The middle section of the front panel would be a piece of brushed gold anodized aluminum mounted behind the main brushed clear anodized one so it would be recessed. It would kind of look like the front panel of Sonic Frontiers equipment!
I would have both the selector switch and volume pot all the way towards the back of the chassis, right in front of the 3 RCA inputs. The audio PCB would be rotated 180 degree from stock and centered right between the rods going to the selector switch and vol pot. I'll have a copper divider panel 6" in from the left side of the chassis to conceal the entire PS section on that side. The whole center section of the chassis would be completely open to the very small crossfeed circuit and a bank of large output capacitors (up to 494uF of Mundorf M-Lytic HV caps per channel). Of course, I would finally upgrade all of the wiring durring this time.
Also, using this chassis would allow me the room to eventually move up to a better amplifier circuit design as well as a much better PS transformer and circuit.
So what do you all think?
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HOTT Modded Xiang Sheng 708B Sennheiser HD600 Sony CDP-397 CD Player FEEDBACK My NEW Website!
Linear Mode
