First time biasing and I have some questions

[pompeiisneaks]

That seems like it might be wrong, but I can't quite tell. That top solder connection is the tip, which should connect to the grid. One easy test is to put your multimeter on continuity mode, and touch the grid and then push down on the tip of the jack until it separates from the swithc and make sure you get continuity.

~Phil

[professormudd]

That seems like it might be wrong, but I can't quite tell. That top solder connection is the tip, which should connect to the grid. One easy test is to put your multimeter on continuity mode, and touch the grid and then push down on the tip of the jack until it separates from the swithc and make sure you get continuity.

~Phil

I do get continuity from the tip to the 33k resistor that the other end of that shielded cable is connected to. I even tested continuity from the tip of my guitar cable to that 33k resistor and it beeped at me.

[pompeiisneaks]

Yes but it might be connected to the wrong spot... I'm not sure though.

That's what I was asking about.

Edit: in other words the physical connectivity from the tip to of the jack to the grid, because if the switch is wired wrong, you'll still get no sound.

~Phil

[professormudd]

Yes but it might be connected to the wrong spot... I'm not sure though.

That's what I was asking about.

Edit: in other words the physical connectivity from the tip to of the jack to the grid, because if the switch is wired wrong, you'll still get no sound.

~Phil

I had also tried to plug into the fx return and got nothing.

Then I looked and saw the connection from the tip of the return to the board was not in place. I replaced it and got sound through the return. I felt stupid, but very happy for a second.

I checked the guitar input, still nothing. I went ahead and took it out and replaced it with a brand new jack, resistor, and run of shielded wire.

I now get significant buzzing noise with the guitar plugged in or not. I can hear the guitar through the speakers but it is a very low volume. I crank all of the pots and still a volume low enough to have a quiet conversation over. The buzz goes away when I crank the presence to 100%, any lower and the buzz comes back.

I also noticed several of the pots felt like the got hung up inside when I turned them passed 11-12 o'clock. I am going to order all new pots and replace all of them. The guy I bought this from had mounted them in the chassis and soldered long runs of wire to all of them, so I am thinking he might have man-handled them.

Do you have any thoughts on the noise and volume?

[professormudd]

Yes but it might be connected to the wrong spot... I'm not sure though.

That's what I was asking about.

Edit: in other words the physical connectivity from the tip to of the jack to the grid, because if the switch is wired wrong, you'll still get no sound.

~Phil

I had also tried to plug into the fx return and got nothing.

Then I looked and saw the connection from the tip of the return to the board was not in place. I replaced it and got sound through the return. I felt stupid, but very happy for a second.

I checked the guitar input, still nothing. I went ahead and took it out and replaced it with a brand new jack, resistor, and run of shielded wire.

I now get significant buzzing noise with the guitar plugged in or not. I can hear the guitar through the speakers but it is a very low volume. I crank all of the pots and still a volume low enough to have a quiet conversation over. The buzz goes away when I crank the presence to 100%, any lower and the buzz comes back.

I also noticed several of the pots felt like the got hung up inside when I turned them passed 11-12 o'clock. I am going to order all new pots and replace all of them. The guy I bought this from had mounted them in the chassis and soldered long runs of wire to all of them, so I am thinking he might have man-handled them.

Do you have any thoughts on the noise and volume?

So like I said, the guy I bought this from had mounted the potentiometers in the chassis and soldered long runs of wire to all of them. He had also soldered a strip of bare wire connecting the backs of every one. I guess he was planning to use it as a ground bus. I ignored it and followed the grounding points as described in the layout.

I ordered some pots and decided to remove that bus wire from the backs of the existing pots.... Man, every pot is a 1M Alpha. Every one of them. The globs of solder on the backs hid the truth from my naive and trusting eyes.

[pompeiisneaks]

Yeah I prefer to just have a bus bar that's not connected to the pots directly. I'd never trust someone else's work without triple checking it.

the hum means often that you have a poor/missing ground connection, and you might also have things miswired to send most of the signal to ground somewhere else? At least you got sound! That's great news.

~Phil

[professormudd]

Yeah I prefer to just have a bus bar that's not connected to the pots directly. I'd never trust someone else's work without triple checking it.

the hum means often that you have a poor/missing ground connection, and you might also have things miswired to send most of the signal to ground somewhere else? At least you got sound! That's great news.

~Phil

I wanted to post a celebratory update. It's alive!

I decided to employ a method I use at work when I am trying to solve a problem. Sit and stare at it. Finally, I am able to see a place where the circuit looks like it should go somewhere, but it doesn't. I check the layout and barely make out a connection that must have been washed out by whatever spilled on this paper.

The buzz is gone, the volume issues are resolved, it sounds like a real amplifier!

I still need to replace the pots to the proper values, but everything is working. I really appreciate everyone's help.

[martin manning]

Finally, I am able to see a place where the circuit looks like it should go somewhere, but it doesn't. I check the layout and barely make out a connection that must have been washed out by whatever spilled on this paper.

Do tell... Where was it?

[professormudd]

Finally, I am able to see a place where the circuit looks like it should go somewhere, but it doesn't. I check the layout and barely make out a connection that must have been washed out by whatever spilled on this paper.

Do tell... Where was it?

Where the second preamp tube pins 1 and 6 connect to the board, the point where the 150k and 220k resistors converge. There is a connection needed from there to filter cap board. There was also a ground missing from where the HRM mid trimmer grounds to the board below, There was no continuity to ground.

https://ampgarage.com/forum/download/fi ... &mode=view

[drew]

If the prior owner built the whole thing with 1M pots, what other stupid shit did he do? You better go through the thing with a fine tooth comb and verify that every single component is what it’s supposed to be.

[martin manning]

Finally, I am able to see a place where the circuit looks like it should go somewhere, but it doesn't. I check the layout and barely make out a connection that must have been washed out by whatever spilled on this paper.

Do tell... Where was it?

Where the second preamp tube pins 1 and 6 connect to the board, the point where the 150k and 220k resistors converge. There is a connection needed from there to filter cap board. There was also a ground missing from where the HRM mid trimmer grounds to the board below, There was no continuity to ground.

https://ampgarage.com/forum/download/fi ... &mode=view

Thanks. The reverb recover stage's connection to the power supply (at 150k plate resistor) is missing too. My guess is that's the other washed-out red wire.

[professormudd]

Do tell... Where was it?

Where the second preamp tube pins 1 and 6 connect to the board, the point where the 150k and 220k resistors converge. There is a connection needed from there to filter cap board. There was also a ground missing from where the HRM mid trimmer grounds to the board below, There was no continuity to ground.

https://ampgarage.com/forum/download/fi ... &mode=view

Thanks. The reverb recover stage's connection to the power supply (at 150k plate resistor) is missing too. My guess is that's the other washed-out red wire.

You made me worry so I double checked. That 150k is connected to the lower-most point that connects to the filter cap board. I haven't hooked up the reverb tank yet to test it.