Kalamazoo Bass 30 project (first post)

[bob p]

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...

I'm back on a PC now, so I can view multiple windows.

First of all, when you measure voltages, it's good practice to specify exactly what you're measuring. So please let us know what kind of voltages you are measuring. When measuring the power supply, it's actually helpful to take both AC and DC measurements at each node and list both.

I'm assuming those are DC measurements. Wow, they're high. You don't have a DC voltage for the OT's center tap (Node A). That is the first voltage that I would write down, as it is the reference point for everything else. It's really important to know. Be sure to get that, and re-measure everything else at the same time that you measure Node A.

Also, we need to know the plate voltage numbers on the tubes, which corresponds to the DC voltage on the OT's outer taps. My recollection is that you got no voltage at the plates, which reflects a problem that needs to be addressed. If you're getting high voltage on the OT center tap but nothing on the tube plates, that doesn't bode well for the status of your OT, and you may need to troubleshoot it.

Node B goes to the screens. That's 490 Volts, presumably DC, without any sort of current limiting resistor. Yikes. Those are some high voltages. Screen dissipation limiters are going to be need to be added in any amp that you'd end up building, especially when voltages are sky-high like these seem to be.

These voltages are going to help define what kind of tubes you can end up using. 6V6 and 6L6 are really under stress at voltages like that.

[aab0mb]

Here's where we're at:

I don't trust this thing. I found by pulling the tubes that one of the tubes had it's alignment pin snapped off. So it was possibly in the amp the wrong way. Lined it up and both tubes seem to light up now although they look a little different color. One more bluish, one orange red color.

Figured i'd try a couple measurements on the plates again just to see if anything stabilized. The plates did stabilize at about 470 volts DC.

I probed the pre amp plates again and they read in the 220-290 DC ranges.

As i was probing the pre amp plates the control panel SPARKED! Not sure what happening there but i'm not looking to blast any more fire out of this thing. Thus my mistrust of said unit.

At this point, i have work to do to get new controls on the chassis. if that happens there's going to be a fair amount of rewiring anyways which makes me thing that my best course will be to dismantle, check component values, measure transformers, etc. Check everything as I go along. I don't feel that i have a firm grasp on the topology which makes tracing and trouble shooting really frustrating. I think a scratch build up could take care of that familiarity problem as well as getting me into a desirable tube configuration. I think that route would have the effect of answering a lot of lingering questions i have about theory as well.

[The Dude]

I found by pulling the tubes that one of the tubes had it's alignment pin snapped off. So it was possibly in the amp the wrong way. Lined it up and both tubes seem to light up now.......

OK............so there were 4 possibilities.

[olddawg]

So... Does it pass signal or not now that the tubes are seated correctly. Why would you randomly start replacing controls? Anytime you have separate modules in an old amp it is a recipe for loose connections and alway more difficult to work on. I would start by resoldering everything. If you do decide to gut it and start over, replace the tube sockets, jacks and pots as well. Could save you a lot of headaches and new ceramic tube sockets are about a buck. However, no matter what you do. If you can't do it safely leave it for someone else.

[aab0mb]

So... Does it pass signal or not now that the tubes are seated correctly. Why would you randomly start replacing controls? Anytime you have separate modules in an old amp it is a recipe for loose connections and alway more difficult to work on. I would start by resoldering everything. If you do decide to gut it and start over, replace the tube sockets, jacks and pots as well. Could save you a lot of headaches and new ceramic tube sockets are about a buck. However, no matter what you do. If you can't do it safely leave it for someone else.

I didn't get to plug it into a speaker once i got the tubes seated correctly because I probed the amp on all the plates once all the tubes were lit. The control panel threw sparks when i probed a preamp tube so i turned the thing off. As i said, if it's throwing sparks and acting funny in general that's where i draw the line, I don't want to keep the tube configuration, and the external control panel is garbage. I'll be able to check each component as i rebuild which seems reasonable This won't be a k'zoo when it's done.

I know how to discharge caps and work with a hand in the pocket when it matters. Fear keeps me safe in most cases.

The reason I plan to move the controls to the chassis is that i got this unit as a homemade "head" configuration. The box was sup par so that was the first to go. The control panel has the power switch on the same control as the treble pot. This doesn't fly with me. The panel controls and the associated leads are known for caused these things to be noisy. I don't plan to keep the control panel as it has asbestos in it IIRC. I'll make a head proper head cab for it once the controls are on the chassis and all should be a lot more robust and sturdy.

I feel the reasons are just.

[olddawg]

I didn't get to plug it into a speaker once i got the tubes seated correctly because I probed the amp on all the plates once all the tubes were lit. The control panel threw sparks when i probed a preamp tube so i turned the thing off. As i said, if it's throwing sparks and acting funny in general that's where i draw the line, I don't want to keep the tube configuration, and the external control panel is garbage. I'll be able to check each component as i rebuild which seems reasonable This won't be a k'zoo when it's done.

I know how to discharge caps and work with a hand in the pocket when it matters. Fear keeps me safe in most cases.

The reason I plan to move the controls to the chassis is that i got this unit as a homemade "head" configuration. The box was sup par so that was the first to go. The control panel has the power switch on the same control as the treble pot. This doesn't fly with me. The panel controls and the associated leads are known for caused these things to be noisy. I don't plan to keep the control panel as it has asbestos in it IIRC. I'll make a head proper head cab for it once the controls are on the chassis and all should be a lot more robust and sturdy.

I feel the reasons are just.

Whatever you do. Do not operate the unit without a load! Sparks in and of themselves don't mean much. As was said before, you might want to get the unit operational if possible. Operational does not in mean perfect working order. You just want to run the thing on the bench to make sure that the PT and OT are functioning without issues and you can list some working parameters that you can note on an original schematic. From what you are describing it sounds like you may have just some stale tubes and bad connections. Once you have established that it is worth rebuilding I suggest that you gut it to the transformers, replace the tube sockets, jacks , and pots. Then build up a new turret board. Use a known good, common layout and schematic and proceed from there. But until you know what you have, it is difficult to decide on what to build. Btw, there is more to safe troubleshooting proceedures than discharging caps.

[aab0mb]

Whatever you do. Do not operate the unit without a load! Sparks in and of themselves don't mean much. As was said before, you might want to get the unit operational if possible. Operational does not in mean perfect working order. You just want to run the thing on the bench to make sure that the PT and OT are functioning without issues and you can list some working parameters that you can note on an original schematic. From what you are describing it sounds like you may have just some stale tubes and bad connections. Once you have established that it is worth rebuilding I suggest that you gut it to the transformers, replace the tube sockets, jacks , and pots. Then build up a new turret board. Use a known good, common layout and schematic and proceed from there. But until you know what you have, it is difficult to decide on what to build. Btw, there is more to safe troubleshooting proceedures than discharging caps.

I appreciate the comments. Working on troubleshooting this thing in a proper fashion but hitting a few roadblocks. Just trying to be safe and learn some stuff.

The turret board might not work because of the tube layout. I'd considered that approach and would prefer it actually. However, the layout of the tubes makes me think that a turret board wouldn't work well. Unless it's ok for a board to be over and on top of the tube sockets....?

"Btw, there is more to safe troubleshooting proceedures than discharging caps."

This is where i usually stand by for more info. I wasn't implying that my safety knowledge is limited to power supply caps. If you have anything to add, however, it's most welcome as it helps pump the resource value of this personally embarrassing thread....

[olddawg]

I appreciate the comments. Working on troubleshooting this thing in a proper fashion but hitting a few roadblocks. Just trying to be safe and learn some stuff.

The turret board might not work because of the tube layout. I'd considered that approach and would prefer it actually. However, the layout of the tubes makes me think that a turret board wouldn't work well. Unless it's ok for a board to be over and on top of the tube sockets....?

"Btw, there is more to safe troubleshooting proceedures than discharging caps."

This is where i usually stand by for more info. I wasn't implying that my safety knowledge is limited to power supply caps. If you have anything to add, however, it's most welcome as it helps pump the resource value of this personally embarrassing thread....

You might want to consider just starting with a new chassis as well. Especially with little experience, layout is very important. The transformers are the expensive parts. You can get a standard aluminum chassis for $25 if you can drill the holes yourself. Look at some websites like Ceriatone, Hoffman, etc. Read up on troubleshooting safety procedures so you don't stop your heart.

[aab0mb]

You might want to consider just starting with a new chassis as well. Especially with little experience, layout is very important. The transformers are the expensive parts. You can get a standard aluminum chassis for $25 if you can drill the holes yourself. Look at some websites like Ceriatone, Hoffman, etc. Read up on troubleshooting safety procedures so you don't stop your heart.

Good points.

The transformer issue brings up another question. My power transformer is prrrrobably going to work. Output transformer is questionable for what i need as ideally i'd like it to be set up to drive an 8 ohm load. It was designed for driving the two 10 inch speakers (which i don't have) in parallel at 16ohms.

After all the advice here. My initial instinct still stands. Tear down then build up checking each part as i go. It just jives with how i've learned electronics up until this point. I'm no pro. Trouble shooting is obviously something that get's easier the more you know the general topology of an amp/pedal/etc. The fact is, i don't feel i know the topology and translation from schematic to circuit like i'm familiar with pedals and such. I realize were my educational downfall is at this point and i'm trying to overcome it. Bottom line is, I'm a visual learner and i need to work in a linear style of learning that makes sense to ME. That being said, this trouble shooting isn't going to necessarily give me what i feel will be a SOLID overview of the amp as it sits. Quite the opposite in fact. Frustrates me to no end. Once I'm familiar with each part and function, all the tracing and trouble shooting will come a lot easier for this and other amps. Same thing with pedals for me. Natural progression.

[The Dude]

If you have anything to add, however, it's most welcome as it helps pump the resource value of this personally embarrassing thread....

Nothing to be embarrassed about. Everybody starts somewhere. Stick with it and have patience.

[aab0mb]

Nothing to be embarrassed about. Everybody starts somewhere. Stick with it and have patience.

That's exactly what i needed. You're a kind person. I'll keep at it because i really do enjoy the triumph when it finally works.

[The Dude]

It was designed for driving the two 10 inch speakers (which i don't have) in parallel at 16ohms.

Two 8 ohm speakers in parallel would be 4 ohms. Actually, if you look at the schematic, the speakers are in series. I'm not pointing this out to nitpick- just so you get it right when you go to build. There are all manners of 16 ohm speakers you could get if you just want a single speaker cab. Also, look over the transformer. There may be extra unused taps on it.

[olddawg]

Two 8 ohm speakers in parallel would be 4 ohms. Actually, if you look at the schematic, the speakers are in series. I'm not pointing this out to nitpick- just so you get it right when you go to build. There are all manners of 16 ohm speakers you could get if you just want a single speaker cab. Also, look over the transformer. There may be extra unused taps on it.

Usually it would be set up for a 16 ohm cab and a 16 ohm extension cab for an 8 ohm load. A one order up or down mismatch is not a problem. My favorite amp has only an 8 ohm tap. I run a 16 ohm 4x 10 cab on it all of the time.

[The Dude]

Usually it would be set up for a 16 ohm cab and a 16 ohm extension cab for an 8 ohm load. A one order up or down mismatch is not a problem. My favorite amp has only an 8 ohm tap. I run a 16 ohm 4x 10 cab on it all of the time.

My point was to explain to the OP that the schematic clearly shows the speakers in series- not parallel. I thought it important that he understands the difference.

[cbass]

I have one of these in think it sounds OK for guitar as is.7591s are cool tubes I'd leave it and maybe tweak a few things.
Its kinda a different animal with gain stages after the cathodyne inverter.you could swap those before the inverter and this thing would scream or squeal
6eu7 are the same as 12ax7 with a different pinout .mine had a Millard and a RCA
Mine had a b+ of around 480 vdc

Oops sorry guys I could only see a few of the posts.i had to jump through hoops to even find the second page on this thread.I don't think my tablet works very well on here.