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"So, all off the capacitors have been replaced with capacitors that are the same resistance but higher voltage." Not same resistance, rather same capacitance. "Would higher voltage capacitors affect sound in any way?" Audible? Most likely, no. Measurable? Slightly different specs...ripple...

Ci7 & 8 are not only blocking DC, but they're part of a high pass filter which allows high frequencies to pass through, but attenuates (reduces) lower freqs. The lower the capacitor value (in microfarads), less low frequencies will pass through, the higher the capacitance value, more low...

Doubtful, but I'd still check voltages there. Are the +/- rail voltages good, or bad, on the affected channel? Regrettably, there won't be a simple solution until you find the issue and that'll take time. Is it a bad component, bad solder joint, broken wire, etc? Grab a cup of coffee, or a...

Is it both channels? If so, start by making sure the power rail voltages are good out to the output transistor emitters. If both (+/-48Vdc) rail voltages are correct and the issue is in both channels, start sniffing around the protection circuit.

Looks like there are 4? switches before the volume control and it's possible the GND connection on one of them is errant. First thing I'd check are solder connections. Might be something as simple as reflowing the solder joints. The fact that the hum changes with volume suggests the issue is...

Pre Out & Main In. Why? Because you're not boosting the preamp signal which can increase distortion/noise, or worse, clip the signal before it hits the power amp section. Were it me, the only ancillary gear I'd hook up would be the eq ... and that would be ONLY if your speakers require an eq for...

A better way to save yourself from continuous fireworks would be to build a DBT (dim bulb tester). There may be more than one thread in the Kenwood forum which diagram how to build one and how it's used. As far as the schematic wiring diagram vs actual PCB connections ... the general rule of...

That's overkill. A KBPC1004W (10A/400V) might be a better choice. First thing to do is find out why the originals tanked.

M4C41 looks like a 300V/4A bridge rectifier. If you do a GOOG search for M4C41, you'll get hits for sale items.

This will work, but you're going to have to solder a piece of wire extension to the wiper lead. Before you order parts, Deoxit the current trimmers and see if it makes a difference. The originals have a carbon track and over time, there's dirt or wear and tear, causing dead spots or sloppy...

"Is there something upstream from the resistor that may be causing the problem?" I don't know, I don't have the unit in front of me to measure voltages, or test any components. I'm throwing darts from afar based on issues I'd seen with a KA-801 restoration I'd performed. Regrettably, there is...

Do you have much of a selection of resistors? If so, nudge the value of R5 & 6 up a bit to say, 39, or 47 and see if it drops the voltage. EDIT: I just noticed this is in the Solid State forum...perhaps the moderators can move this to the Kenwood forum.

I wouldn't chance leaving it on. Are the trimpots (VR1 & 2) set all the way to one side? ...and do they make a difference as you turn them?

Okay, with the amp on and warmed up, volume all the way down and nothing hooked up to the speaker terminals or inputs, what do you measure -- in mV -- between CP3/5 & CP4/6? Should be 26mV.

Ok ... what you're referring to as a "preamp" is actually the PHONO stage. It's ONLY purpose is to equalize and boost the signal from a phono cartridge. When you switch from PHONO to AUX or TUNER, the PHONO circuitry is no longer in the signal path. However, a short there can affect the rest of...

They're in the signal path and block DC before your tone control and power amp circuits, and establish your bass corner (cutoff) frequency. Less capacitance, higher frequency cutoff, higher capacitance, lower frequency cutoff. Something else to consider ... the restoration of the 7100 may have...

Check Ci7 & 8 and make sure they're 10uF and not lower. Did the rebuilder pull any switches completely apart to clean them? Kinda wondering whether he did the Subsonic filter switch and has something back asswards. You can also download a 40Hz tone to your phone and pipe it through both the 5600...

What Pete said. Transistor oscillation/thermal runaway can cause your issue. His suggestion for focusing on Q13 & 15 is a good one since both those transistors have Miller caps (22pF) and both affect bias control. It's possible that replacement transistors can cause original transistors to...

According to the service manual/schematic -- which could be wrong -- Q17 & 19 are BCE pinouts and your replacements are ECB. That said, the board silkscreen should denote a correct orientation.

For a better understanding of headphone output series resistance, take a gander at these posts from @ecluser (posts #6 & #10).

I would test with both headphones (cans) and speakers. The cans are tapped off the amplifier output, but the speakers have the speaker selector switch between the amp output and speaker binding posts. If there's a difference in volume with the speakers, the selector switch may need a cleaning.

If you look closely at that pic I'd posted -- though it may be difficult to tell -- it looks like Qe1 & 2 are just one transistor. That's because one is folded over the other and the plastic housings are glued together. Why? Differential pairs tend to track better when thermally coupled. As far...

The 7300 & 8300 share the same circuit topology, just slightly higher voltage, a TA-100W instead of a TA-80W, and some different part values in the 8300. If you want to lower DC offset, play with the value of Re5. Schematic calls for 5.6K, but judging by your pics, there's a 6.8K stuffed in...

That'll work, but I'd still leave it external to the unit. I restored a Trio KA-8100 and this was the solution I used for a step down x-former. Granted, there was no room inside the 8100 to install a step down tranny, but it's also easy to hide an external unit. I actually looked at the Nissyo...

Passive components are those which do not generate power. Examples of these are resistors and capacitors. What I'm about to say is important to the conversation, but not meant to be critical...if one cannot read a schematic, it can create a serious issue(s) which at the very least, could blow a...