This isn't making sense to me. Anybody?
Debugging help: Brownface vibrolux edition
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martin manning
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Re: Debugging help: Brownface vibrolux edition
Not a bit.
Re: Debugging help: Brownface vibrolux edition
maybe I'm using incorrect terminology. Right after the signal goes from the choke to the first signal step-down resistor, I put an extra resistor. Is this not what Martin meant? I again have absolutely no idea what I'm doing, so i could have done something completely wrong. Sorry if I misinterpreted what you said. LMK if I should try something different.
Sorry bout that,
Matoni
Sorry bout that,
Matoni
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martin manning
- Posts: 14308
- Joined: Sun Jul 06, 2008 12:43 am
- Location: 39°06' N 84°30' W
Re: Debugging help: Brownface vibrolux edition
Yes, and you're wasting people's time by doing so. The screen resistors are the 470 ohm connected to the 6L6 screen grids, at pin 4. sluckey pointed that out earlier in the thread.
That is exactly what I suggested, however if you refer to a schematic you need to be sure everyone knows exactly which one, and which components you are talking about. Better yet mark one up and post it. If you use the wrong name for a part, everyone will be looking somewhere else. For example A, B and C voltages have historical meanings (heater, plate, and bias). The letters in boxes on the Fender schematics are their own notation for power supply and sometimes other circuit nodes. And BTW, there shouldn't be any "signal" on the DC power supply rail. Signal voltage (which is AC) starts at the input jacks and flows through the amp to the speaker.matoni wrote: ↑Fri May 05, 2023 2:06 amRight after the signal goes from the choke to the first signal step-down resistor, I put an extra resistor. Is this not what Martin meant? I again have absolutely no idea what I'm doing, so i could have done something completely wrong. Sorry if I misinterpreted what you said. LMK if I should try something different.
I still have doubts about the plate voltage. Do you know what the idle current through the 6L6's is? Do you know how to measure and set the bias? That is important to sound quality and tube life, and in the case of this circuit, proper operation of the tremolo. The idle current will affect the plate voltage significantly, so you need to get that settled to determine what screen node voltage you have (at the junction of the choke and the first dropping resistor), and then worry about adjusting the downstream (preamp) voltages.
If you are just 16 and got this far, that's great, but learning to speak the language is essential.
Re: Debugging help: Brownface vibrolux edition
sorry if you think I'm just wasting your time, I promise that's not what I'm trying to do. I'm trying to learn as much as I can about this, and I really appreciate your help.
When I get home from school, I will post a marked-up schematic with all of the voltages going to the plates (I think they're called the plates at least... I'm starting to question all of my knowledge) of the preamp tubes, the screens of the power tubes (and the tremolo circuit) as well as the bias, and the voltage going into the phase inverter.
Sorry for wasting your time. I am only 16, and I've only built a few amps (from kits) and am not completely sure what I'm doing. Thanks for helping me along this journey. I greatly appreciate it.
When I get home from school, I will post a marked-up schematic with all of the voltages going to the plates (I think they're called the plates at least... I'm starting to question all of my knowledge) of the preamp tubes, the screens of the power tubes (and the tremolo circuit) as well as the bias, and the voltage going into the phase inverter.
Sorry for wasting your time. I am only 16, and I've only built a few amps (from kits) and am not completely sure what I'm doing. Thanks for helping me along this journey. I greatly appreciate it.
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martin manning
- Posts: 14308
- Joined: Sun Jul 06, 2008 12:43 am
- Location: 39°06' N 84°30' W
Re: Debugging help: Brownface vibrolux edition
My point is it will take extra time for people here to figure out what your situation is and what you are asking about if you can't communicate clearly.
I gather the amp is working now, but I don't know how it got that way from where it was. There must be more to it than just the addition of that extra 10k.
You absolutely need to measure the power tube idle current and get the bias set correctly. I see you have the schematic values for the resistors in the bias supply, and the chances of that landing correctly are not very good. Unless you have a bias probe, it looks like you will have to use the OT primary resistances (red to brown, and red to blue) to calculate the current going through each power tube (Vred - Vbrown)/Rred-to-brown and (Vred - Vblue)/Rred-to-blue. I would do that first thing.
A voltage survey is a good idea, and a good diagnostic technique. That means getting DC voltages from the tube pins like this, with the tremolo turned off:
Preamp tubes
V1 <Vpin 1> <Vpin2> <Vpin3> <Vpin6> <Vpin7> <Vpin8> (plate, grid, cathode, plate, grid, cathode)
V2 <Vpin 1> <Vpin2> <Vpin3> <Vpin6> <Vpin7> <Vpin8>
Tremolo Oscillator
V3 <Vpin 1> <Vpin2> <Vpin3> <Vpin6> <Vpin7> <Vpin8>
Phase Inverter
V4 <Vpin 1> <Vpin2> <Vpin3> <Vpin6> <Vpin7> <Vpin8>
Power Tubes
V5 <Vpin 3> <Vpin4> <Vpin5> (plate, screen, control grid)
V6 <Vpin 3> <Vpin4> <Vpin5>
I'm assuming you can do this without shorting anything. Clip the black lead of your meter to the chassis, and probe with the red one. Measure from the board when you can to avoid poking around the 9-pin sockets.
I gather the amp is working now, but I don't know how it got that way from where it was. There must be more to it than just the addition of that extra 10k.
You absolutely need to measure the power tube idle current and get the bias set correctly. I see you have the schematic values for the resistors in the bias supply, and the chances of that landing correctly are not very good. Unless you have a bias probe, it looks like you will have to use the OT primary resistances (red to brown, and red to blue) to calculate the current going through each power tube (Vred - Vbrown)/Rred-to-brown and (Vred - Vblue)/Rred-to-blue. I would do that first thing.
A voltage survey is a good idea, and a good diagnostic technique. That means getting DC voltages from the tube pins like this, with the tremolo turned off:
Preamp tubes
V1 <Vpin 1> <Vpin2> <Vpin3> <Vpin6> <Vpin7> <Vpin8> (plate, grid, cathode, plate, grid, cathode)
V2 <Vpin 1> <Vpin2> <Vpin3> <Vpin6> <Vpin7> <Vpin8>
Tremolo Oscillator
V3 <Vpin 1> <Vpin2> <Vpin3> <Vpin6> <Vpin7> <Vpin8>
Phase Inverter
V4 <Vpin 1> <Vpin2> <Vpin3> <Vpin6> <Vpin7> <Vpin8>
Power Tubes
V5 <Vpin 3> <Vpin4> <Vpin5> (plate, screen, control grid)
V6 <Vpin 3> <Vpin4> <Vpin5>
I'm assuming you can do this without shorting anything. Clip the black lead of your meter to the chassis, and probe with the red one. Measure from the board when you can to avoid poking around the 9-pin sockets.
Re: Debugging help: Brownface vibrolux edition
Hi Matoni,
First, it's great you are taking an interest in such an arcane activity/hobby (tube amps), particularly as a younger person. It can be difficult to convey information or respond to what is being asked of one if they don't really have a basic understanding of the topic, and electronics (even tube electronics) has a degree of complexity that needs some time to digest and understand. Making your own PCB is on the face of it commendable, but it was probably not the easiest way to ensure success because it introduces other variables.
One of the issues here is we don't have any comprehensive idea of your build through photos, schematic, board layout, components, etc. You've got some of the smartest, most accomplished folks on this forum trying to help you, so the fact that they are having difficulty suggests that you might be better prepared to only ask questions on a forum like this, with pretty sophisticated builders, if you step back and do some reading of tube amplification books. If you can't afford or don't want to invest in any, some of the build guides by the few guitar amp kit providers are very detailed and can be useful in at least understanding the topology, terminology, and components involved.
I grew up learning about tube electronics 50 years ago from my engineer father, but only to the degree that I wanted to keep my Bandmaster alive when playing in bands. I learned new things pretty much only when a problem arose. That set me back, because I didn't get as much of the basic understanding down first. When I first started building amps only about 10-12 years ago, I had already repaired several, and had bought maybe 8 books on the subject so I could immerse myself in the information.
These folks aren't picking on you, but they really can't help you as much as they could if you can do some deeper reading of materials other than forums, which tend to be very subject or project-specific (or inaccurate) and either assume or omit a lot of the other details needed to understand what is happening. The more organized you can be with the relevant components and data, such as specific voltages, etc., the better able people are to help. But keep in mind, a forum is not like school, where the teachers are tasked with and paid to teach students. You will get better results if you can huddle by yourself with the right materials (some accurate stuff is also on the internet) until you have some breakthroughs in understanding the topic.
Keep at it!
Greg
First, it's great you are taking an interest in such an arcane activity/hobby (tube amps), particularly as a younger person. It can be difficult to convey information or respond to what is being asked of one if they don't really have a basic understanding of the topic, and electronics (even tube electronics) has a degree of complexity that needs some time to digest and understand. Making your own PCB is on the face of it commendable, but it was probably not the easiest way to ensure success because it introduces other variables.
One of the issues here is we don't have any comprehensive idea of your build through photos, schematic, board layout, components, etc. You've got some of the smartest, most accomplished folks on this forum trying to help you, so the fact that they are having difficulty suggests that you might be better prepared to only ask questions on a forum like this, with pretty sophisticated builders, if you step back and do some reading of tube amplification books. If you can't afford or don't want to invest in any, some of the build guides by the few guitar amp kit providers are very detailed and can be useful in at least understanding the topology, terminology, and components involved.
I grew up learning about tube electronics 50 years ago from my engineer father, but only to the degree that I wanted to keep my Bandmaster alive when playing in bands. I learned new things pretty much only when a problem arose. That set me back, because I didn't get as much of the basic understanding down first. When I first started building amps only about 10-12 years ago, I had already repaired several, and had bought maybe 8 books on the subject so I could immerse myself in the information.
These folks aren't picking on you, but they really can't help you as much as they could if you can do some deeper reading of materials other than forums, which tend to be very subject or project-specific (or inaccurate) and either assume or omit a lot of the other details needed to understand what is happening. The more organized you can be with the relevant components and data, such as specific voltages, etc., the better able people are to help. But keep in mind, a forum is not like school, where the teachers are tasked with and paid to teach students. You will get better results if you can huddle by yourself with the right materials (some accurate stuff is also on the internet) until you have some breakthroughs in understanding the topic.
Keep at it!
Greg