It Takes a Village (I'm the Idiot) | JMI Vox AC50 Part 8

Added: 2026-05-09

[00:00:00]Back with this AC 50 and I think I might have solved the mystery issue. See these three lugs here?

[00:00:05]These three tags, they're all tied together by this bit of wire. If I measure continuity from one all three of them have continuity. Then you have four lugs that are also joined by a bit of wire on the back. If I go here to here continuity here continuity here Uh-oh.

[00:00:26]Uh-oh.

[00:00:27]That bit of wire somehow has just missed the bit of metal over here. So this one's not actually tied to ground with the others. This is the phase inverter ground. And these two wires that are going to this lug are the base pot ground wires. So the base pots are not working entirely properly in this amp.

[00:00:47]And that could be certainly the cause of our mystery issue because in addition to being pots and part of the tone stack, they are also grid leaks for some coupling caps. And the reason we're not getting total blocking distortion nasties is because the treble pot wipers come through these 470k resistors to here, which then have a path to that same ground through this one meg. So the tone stack as a whole is still operating but not optimally. So let me get these this old solder out and recreate this connection, reflow that, and see where we're at. Because of where I need to work and where the camera is, I can't really show you this bit. I'm just going to get the solder sucker and braid, get the old solder out. Uh reconnect it with a bit of 22 gauge bus wire, then reflow all that.

[00:01:38]This bastard from 1965 was never soldered at the factory. This ground was used, that lug was used for ground as the amp came in.

[00:01:47]Never soldered.

[00:01:49]But now So let's see what the amp sounds like now. It's possible that that was part of the issue, but not the entire thing.

[00:02:02]We'll find out. All right. Let's take this out of standby.

[00:02:09]All right. I can tell you that it's a lot louder than it has been, just in terms of the self noise of the amp.

[00:02:15]And there is a buzz that I'm not a fan of. This not heater buzz or ground loop buzz.

[00:02:21]Um that I can hear now, and that might just be because the output transformer is hanging out in space.

[00:02:27]We'll We'll jump off that bridge when we come to it.

[00:02:32]But, it's not in the preamp. Let's see how this thing is sounding now. It seems considerably louder.

[00:02:38]>> [music] [music] [music] [music] [music] [music] >> That's the classic AC50 sound. Now, ours was already getting break breakup when I was here before.

[00:03:20]It's staying a lot cleaner now.

[00:03:23]>> [music] [music] [music] [music] [music] [music] >> Let's see how the other channel is doing.

[00:04:06]>> [music] [music] [music] [music] [music] >> Still not my favorite by itself. It sounds fantastic when you use the both of them blended together.

[00:04:40]But that problem seems to be gone.

[00:04:42]So, let's see. What next? I want to address the remaining buzz there. I'm hearing some ripple.

[00:04:51]Uh that might be mismatched output tubes.

[00:04:55]Though, if I pull the phase inverter, it gets dead silent. It could be the heater dress around here.

[00:05:01]Could be a lot of things. I don't really like um or trust this old shielded wiring here.

[00:05:07]Gets finicky over the decades.

[00:05:10]I might replace that.

[00:05:12]Uh I will find out what I need to find tomorrow.

[00:05:16]But we are in a much better place now.

[00:05:18]It's even possible that Now that that underlying problem is gone, the old output transformer might make it without going We shall see. No promises, but fingers crossed.

[00:05:31]Thanks for watching.