Kalamazoo Bass 30 project (first post)

[The Dude]

Yeah,......those voltages don't make sense. I don't see plate or screen values there anywhere. Either you have a power supply issue or you read them incorrectly. Are those DC voltages you listed on the 7591's? Or, maybe you didn't have a good ground reference for your meter? Or, as you say, maybe your meter is flaky?

[aab0mb]

I'll try to draw up the schematic and write in the voltages. Should be a good learning experience although the jacked up blood pressure from the high voltage risk is something i can do without... Safety first.

Measuring DC for all the voltage readings listed. Can't replace the tubes as i only have common guitar tube types around. Kind of why i wanted to maybe convert this thing to a more common configuration. I agree that it'd be cool to hear it in it's native state. However, as one of the power tubes seems to be shot I can't see myself ordering the original tube types. Might as well build it up for commonly available tubes. That being said, if this IS in fact going to be converted to common tube types, would my best best be to rip it down and start fresh? My gut instinct is that i'll learn more and have a better understanding of the amp once it's functioning. I'm really wanting to learn just as much as i want something that makes noise.

As far as I know the ground was correct. The circuit uses a few places on the attached terminal strips to ground to the chassis. I used one of those. Perhaps I should use a different point as reference? This thing still needs a 3 prong power cable. Could this be something that's messing up my readings?

I think I had some strange readings on this meter during another project. It's one of the ultra cheap ones so i should buck up and grab a semi robust meter.

[aab0mb]

Forgot to mention the 6600R sounds right for the primary Z. I think i came across that figure in some research about the amp. Yes, the speakers are or where two 10" speakers wired in series.

[The Dude]

Can't replace the tubes as i only have common guitar tube types around.

What olddawg was suggesting was not replacing the power tubes. Rather, swap them into different positions and see which one "lights". By your description, the filament was not glowing in one of the tubes. If you swap them into different positions does the problem follow the tube or the socket? This will tell you if the tube itself is bad or if something is wrong inside the amp. You could also measure the resistance between pins 2&7 on the tube and see if the filament measures open. Either way, you can do this without having to get new tubes.

You say, "I'm really wanting to learn just as much as i want something that makes noise." Whether you fix the amp, or build another amp into this chassis, if your goal is to learn something, I'd recommend fixing the amp first. This will teach you a lot about how the thing works- probably more so than a build. You'll learn more having to figure something out than you will just following directions from a kit or building something from a diagram.

Just my $.02.

[bob p]

^ Yes.

[The Dude]

To elaborate further:

You're going to use the same sockets, transformers, and likely much of the other circuitry even if you do a fresh build, so you might as well fix it anyway. That will eliminate "built in" problems with anything you decide to make of it.

[aab0mb]

great advice coming in here.

I'll swap the tubes to see if it is in fact a dead one. Good advice. Should have thought of that!

I like the tip about fixing the amp first as a learning experience. If the tubes prove to be good then i think we can take that road.

If i have a burned up tube then what? Go ahead with the simplest conversion to a different tube type and leave everything else the same to start? Seems like a good idea. Also might be cool to hear an amp with 6L6s and 6eu7s.

Off to the bench. I'll report back.

[aab0mb]

Tried swapping tubes and got a crazy loud hum. Shut the amp off.

Pulled the tubes and flipped it back on. No buzz. Probed the plates which now read 490-500 volts. It dropped about 10 volts over a couple minutes and then was stable.

tried to gather some more readings before my dyslexia kicked in and i needed a break.

I noted the voltages on the power supply section for the lettered points

D: 379 volts

C: 372 volts

B: 490 volts

A: dyslexia got the best of me here. I'll get it though...

[aab0mb]

Also, i noticed that these power tubes are wired up differently? One has pin 1 in use and the other does not. I wonder if someone already tried to rebuild this thing, botched it, then gave up.

[bob p]

in general, it's a good idea to present the data so that people who are trying to help you don't have to jump through hoops to figure it out.

i'm working on a mobile display tonight and i can't see the data to help you because I can only see one page at a time, but your data is in a post on page 2 while the schematic is in a post on page 1. i asked you to consolidate the data a couple of times. maybe if you put all of the data in one place I could help you, but until you do that, i can't.

sorry.

[The Dude]

Also, i noticed that these power tubes are wired up differently? One has pin 1 in use and the other does not. I wonder if someone already tried to rebuild this thing, botched it, then gave up.

Pin 1 on the 7591 is unused. They are just using it for a terminal strip to connect something else. The fact that the socket pin is used on one tube and not the other doesn't mean anything.

[aab0mb]

in general, it's a good idea to present the data so that people who are trying to help you don't have to jump through hoops to figure it out.

i'm working on a mobile display tonight and i can't see the data to help you because I can only see one page at a time, but your data is in a post on page 2 while the schematic is in a post on page 1. i asked you to consolidate the data a couple of times. maybe if you put all of the data in one place I could help you, but until you do that, i can't.

sorry.

Color me red. Never done this before. I'll try to step it up. Doing my best here.

[The Dude]

On the point of "no filament on one tube symptom": After looking at a picture of the amp, there are two green wires coming from the power transformer to one of the output tubes, then jumpered to the other output tube (black and white wires), then jumpered to the preamp tubes. Since you have filament voltage to the preamp tubes (presumably, or you would have mentioned otherwise) we know that filament voltage is making it all the way there. That leaves 3 possibilities.

1) The filament is open in that tube (check with ohm meter across pins 2&7 with tube out of amp).
2) There is a connection problem on the suspect socket allowing filament voltage to pass but not connected to the actual pin of the socket.
3) The socket or socket pin is bad- not making connection to the tube.

[aab0mb]

Those voltages don't say much, other than your plate voltages aren't reliable enough to measure.

Are you measuring AC or DC?

I'd trace voltages through the power supply and write them on the schematic. Doing that spares everyone from having to read the data sheet and saves us time.

I'd like to execute this. How do most people go about presenting this info? Draw it by hand? I have no printer or that would be easy. Some kind of paint program?

[bob p]

whatever works. sometime people will draw a sketch. some will print a schematic, write on it, and scan it or take a picture. some people will use an image editor. others will just explain their measurements, like saying something like "I get voltages of X and Y on the first and second filter nodes, 450VDC on the power tube plates, 360 V on the screens," etc.

it doesn't really matter which way you do it, the key is to just consolidate all of the information to try to make it easy for someone to follow along. if you're using an uncommon tube, then it really helps to have all of the information in one place so that someone doesn't have to go looking at your post, at the schematic, and at a tube data sheet to tie all of the information together.

there are many good ways to convey the information so that people don't have to go hunting to put it into perspective. for the common tubes, many people here will know the pin numbers by heart, so it's fine to just list voltages by pin numbers. for uncommon tubes people might not have the pinouts in their heads, which means that we have to look things up. that's not usually a problem, but for me it's hard tonight because my web access is limited to a hand held device.