Cathode follower without elevated heater voltage

[Dark Mavis]

Since you can't remember if the hum was there or not you should err on the safe side and do some current checking before going any further. We already checked for grid bias negative voltage, right? If not then you need to do that and also check bias current. There are a few ways to do that and perhaps you already know one or more. Otherwise we can help. After that you'd test voltage at each power supply node. If anything starts getting too hot or if any tubes start to glow at their plates you'll want to power down immediately.

I don't think the hum was there before the re-wire, but I'm pretty sure it was there when the amp "worked". I don't think I checked bias voltage. I'll do that tomorrow, and check bias current and all the other voltages I checked before, plus the power supply voltages

[Dark Mavis]

Since you can't remember if the hum was there or not you should err on the safe side and do some current checking before going any further. We already checked for grid bias negative voltage, right? If not then you need to do that and also check bias current. There are a few ways to do that and perhaps you already know one or more. Otherwise we can help. After that you'd test voltage at each power supply node. If anything starts getting too hot or if any tubes start to glow at their plates you'll want to power down immediately.

Well, I never got far into the checks before finding a problem.

Bias -41.1v
B+1 502v
B+2 0v

I guess that's why no sound from the speakers? And, I guess that means the big resistor between B+1 and B+2 is burnt out? But if so, the timing of it is worrysome. Cus it wasn't burned out before. I'll check it anyways.

Edit: It's actually not 0v. It's about 5v. The same 5v that stays on all the caps after that first resistor, for quite a while after the amp is off. Also, it says on the resistor that it's a 2.2k, but I swear I remember the schematic showing 10k - though that was an output section with 2 6L6's and different filter cap values.

Edit. Nope. It reads 2.2k. I pulled it out and measured it. I don't get why there's no voltage on that side of it

[Chuck H]

Well you'll need to be sure you're looking at it right. And if you are you'll want to measure ohms to chassis from the 0V end of that 2.2k resistor. There may be a wiring error. Lot's of possibilities. The power supply diagram you posted is unclear and almost certainly not accurate as it shows NO resistor between the plates and screens. There is likely a choke (looks like a transformer but only has two wires) The 2.2k would probably be feeding the phase inverter. I don't know. I do know that diode in series shouldn't be there. So there's still some confusion about how it's supposed to be. Please post the diagram or schematic you have that shows the 10k resistor rather than a redraw. Otherwise I'm going to ask you to trace the whole power supply circuit manually

[Dark Mavis]

Well you'll need to be sure you're looking at it right. And if you are you'll want to measure ohms to chassis from the 0V end of that 2.2k resistor. There may be a wiring error. Lot's of possibilities. The power supply diagram you posted is unclear and almost certainly not accurate as it shows NO resistor between the plates and screens. There is likely a choke (looks like a transformer but only has two wires) The 2.2k would probably be feeding the phase inverter. I don't know. I do know that diode in series shouldn't be there. So there's still some confusion about how it's supposed to be. Please post the diagram or schematic you have that shows the 10k resistor rather than a redraw. Otherwise I'm going to ask you to trace the whole power supply circuit manually

I actually took the resistor out of the amp to measure it. That's how sure I was that it must be dead. I have a sketch of the power supply - the one that's actually in the amp. I'll draw it out nice in photoshop, cus it's a pencil drawing on a tea stained utility bill. That resistor is directly between B+1 and B+2, so I don't see how there could be no voltage on the B+2 side of it if it still reads 2.2k. Maybe the probe never got a good contact...Or maybe there's a bad solder joint, cus I put the probe on the lead into the cap, rather than the terminal it's soldered to, cus it was easier to reach. Anyways, I'll post that diagram tomorrow. I also want to try reading that same voltage directly from the end of the resistor - cus there's a jumper from there to the cap at B+2 (The orange wire you can see in the photo, except in the photo it's wired to the wrong cap. I fixed that.
One other possibility...MAYBE I forgot to take the amp out of standby. I seriously doubt it, but it's one other possibility. I'm quite capable of forgetting something like that

[Chuck H]

I'll draw it out nice in photoshop, cus it's a pencil drawing on a tea stained utility bill.

I have many, many inspired circuits drawn on such things. Some I haven't gotten to playing with yet and haven't been transferred to anything better.

That resistor is directly between B+1 and B+2, so I don't see how there could be no voltage on the B+2 side of it if it still reads 2.2k. Maybe the probe never got a good contact...Or maybe there's a bad solder joint, cus I put the probe on the lead into the cap, rather than the terminal it's soldered to, cus it was easier to reach.

Or... That other side of the resistor is accidentally grounded to 0V in some way. That might explain the transformer humming. Heavy load, but not quite enough to blow the fuse? Something else to check.

MAYBE I forgot to take the amp out of standby. I seriously doubt it, but it's one other possibility. I'm quite capable of forgetting something like that

I do that sort of thing often enough that I couldn't possible roll my eyes at that. The good people here have been very patient with me.

[eschertron]

One other possibility...MAYBE I forgot to take the amp out of standby. I seriously doubt it, but it's one other possibility. I'm quite capable of forgetting something like that

Or the standby switch is broken? Any extra components provide extra failure modes. Regardless of how the amp behaved in the past, troubleshoot what it's doing (or not doing) now.

[Dark Mavis]

Or the standby switch is broken? Any extra components provide extra failure modes. Regardless of how the amp behaved in the past, troubleshoot what it's doing (or not doing) now.

Yeah. Or that. from B+1 to B+2, there's only the standby switch and that resistor, and the associated wiring. It's gotta be simple. Maybe just a grubby probe, even. Actually...the amp is right next to me. One sec...Nah. Standby switch works and I get continuity everywhere there should be. Maybe I just never got a good connection when I tested

Edit. Oh dear. 442 volts. I guess I forgot to take it out of standby. Let's pretend this never happened

Edit: So...So far we got

Bias -41.1v
B+1 502v
B+2 442v
B+3 391v
B+4 388v
B+5 0v

And I see exactly why I got 0 volts at B+5. I'd forgotten about those empty eyelets when I rebuilt the power supply. Guess where I wired the B+ wire from the main circuit board to? Yup. My preamp is getting power from an empty eyelet. Let's pretend THIS never happened, either

Edit 225v now on B+5 but still nothing from the speaker

[jmaf]

Yeah. Or that. from B+1 to B+2, there's only the standby switch and that resistor, and the associated wiring. It's gotta be simple. Maybe just a grubby probe, even. Actually...the amp is right next to me. One sec...Nah. Standby switch works and I get continuity everywhere there should be. Maybe I just never got a good connection when I tested

Edit. Oh dear. 442 volts. I guess I forgot to take it out of standby. Let's pretend this never happened

Edit: So...So far we got

Bias -41.1v
B+1 502v
B+2 442v
B+3 391v
B+4 388v
B+5 0v

And I see exactly why I got 0 volts at B+5. I'd forgotten about those empty eyelets when I rebuilt the power supply. Guess where I wired the B+ wire from the main circuit board to? Yup. My preamp is getting power from an empty eyelet. Let's pretend THIS never happened, either

Edit 225v now on B+5 but still nothing from the speaker

If you inject some signal directly to the PIV does it come out the speakers?

I used to have one of those pedals that record guitar playing, I'd have a cable with a 600V capacitor on the other tip instead of a phone plug. I could touch the tip to whatever tube I wanted to inject instant guitar playing anywhere in the amp. That way you find where you're losing signal.

[Dark Mavis]

If you inject some signal directly to the PIV does it come out the speakers?

I used to have one of those pedals that record guitar playing, I'd have a cable with a 600V capacitor on the other tip instead of a phone plug. I could touch the tip to whatever tube I wanted to inject instant guitar playing anywhere in the amp. That way you find where you're losing signal.

I don't even know what PIV is. But...maybe I can check at the effects send. I just don't have a spare amp. Also...I don't get continuity to ground from the negative side of the B+5 cap, so that's something to check tomorrow too

[jmaf]

I don't even know what PIV is. But...maybe I can check at the effects send. I just don't have a spare amp. Also...I don't get continuity to ground from the negative side of the B+5 cap, so that's something to check tomorrow too

PIV = the last preamp tube before the power tubes. (Phase inverter). The effects return should inject signal there. If you have an external preamp (pedal/boost/whatever) you can inject your guitar sound directly to the effects return.

[Dark Mavis]

PIV = the last preamp tube before the power tubes. (Phase inverter). The effects return should inject signal there. If you have an external preamp (pedal/boost/whatever) you can inject your guitar sound directly to the effects return.

How about an MP3 player via a 1/4 inch adapter? Ah. I know what the phase inverter is. Just never heard it called that. I'm totally new to all this so it's a lot to learn in a short space of time

[nosaj]

How about an MP3 player via a 1/4 inch adapter?

Still put a cap on the the probe end coming from the mp3 player to protect it.

nosaj

[Dark Mavis]

Okay, I measured the plates and Cathodes of the preamp tubes. It was all I had time for right now. I measured the grids on a couple tubes but it was really low and moving around a lot

Bias -41.1v

B+1 502v
B+2 442v
B+3 391v
B+4 388v
B+5 225v

V1-1 126v
V1-2
V1-3 0.832v
V1-6 225v
V1-7
V1-8 76v

V2-1 124v
V2-2
V2-3 1.51
V2-6 123v
V2-7
V2-8 1.54

V3-1 128v
V3-2
V3-3 1.18v
V3-6 225v
V3-7
V3-8 37v

V4-1 144v
V4-2
V4-3 1.13
V4-6 164v
V4-7
V4-8 1.4

V5-1 325v
V5-2
V5-3 2.51
V5-6 172v
V5-7
V5-8 1.29

V6-1 175v
V6-2
V6-3 73.2
V6-6 186v
V6-7
V6-8 73.2

[Dark Mavis]

Or... That other side of the resistor is accidentally grounded to 0V in some way. That might explain the transformer humming. Heavy load, but not quite enough to blow the fuse?

Doesn't seem to be. And I got voltage there now. I guess I must have forgotten to flip the switch.

[Chuck H]

Doesn't seem to be. And I got voltage there now. I guess I must have forgotten to flip the switch.

As I said, it happens to the best of us... Or at least me

Some of those voltages do look questionable. The problem is identifying their location in the circuit. I know you've posted some of the actual tube lineup relative to gain stage progression, but maybe a primer now would be a good thing. Also, V1b and V3b are pretty clearly the cathode follower stages. It would be good to have the grid pin voltages for AT LEAST those.

P.S. You're hanging in well. And I hope you're having some fun.