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Old 25th November 2008, 06:31 PM   #1
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Unhappy K-16ls

There are some tricky details here.

So I built a K-16LS from www.s5electronics.com as my first ever electronics project. I have very little electrical background. I'm a computer scientist, not an electrical engineer. So the K-16LS amp was good and I learned a bit about the process and I decided to build another one and mount it in a chassis, and get a better on/off switch, etc. I just couldn't see myself using the amp mounted on a board. It seems to unsafe, or breakable.

So for the next kit I got some different components, like chassis-mount tube sockets, and a beefy on/off switch, and some nicer bananna plugs, etc. I also wrapped the chassis in tolex for some reason. I thought it might look better... who knows. I certainly don't think it looks great, but what the hey.

Attached are URLS to some photos of my wounded amp, and an audio sample of what happens when I turn it on.

The wiring is pretty ridiculous, as it's my first project where I had to lay anything out and I discovered I'm not very smart at this. I wired the tube sockets up and around and back into the top (bottom) of the circuit board.

Note: I have "unplugged" the bananna plugs from the chassis, because I think this might be a problem area...

Questions:

1. Am I supposed to insulate the bannana plug outputs from the metal chassis? Does the chassis eat the output signal? What about the RCA inputs? Is there something that is destroying the output signal by touching the chassis?

2. Am I supposed to wire a little ground to all of the power transformers, under a mounting nut? Does anyone know what I'm talking about?

3. Can anyone help me to figure out why it sounds so awful? NOTE: See those two red wires sticking out? Those go to the bananna plugs for the right channel. When I recorded that mp3, I just touched the ends of the speaker wire to the raw ends of the two red wires. Also note how it sounds pretty good for a few seconds, then distorts.


URLs to bad photos and an audio clip:

http://diytube.pghmenus.com/Photo%204.jpg
http://diytube.pghmenus.com/Photo%205.jpg
http://diytube.pghmenus.com/Photo%206.jpg
http://diytube.pghmenus.com/Photo%207.jpg
http://diytube.pghmenus.com/Photo%208.jpg
http://diytube.pghmenus.com/amp.mp3

I took the bad photos and audio with the built-in camera and speakers on my MacBook Pro. The "click" at the beginning of the audio sample is me turning the amp on. Then it warms up and the music fades in, sounds good, then it distorts. After it distorts I take the speaker wire away from the two raw red wires. You can imagine that when it totally cuts out it's my hand jittering.

Thanks for checking out my post. I really hope someone can help, otherwise I will cry.
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Old 25th November 2008, 07:30 PM   #2
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Default Additional details

I uploaded another audio sample and another photo.

http://diytube.pghmenus.com/amp2.mp3
http://diytube.pghmenus.com/Photo%209.jpg

I am aware of several problems:

1. The binding posts were touching the chassis. Tube amps are sensitive to ovlerloads. Is it possible I damaged one or more components with a short? I have backup components. Is it likely that I damaged my tubes? Is it safe to try replacing them after isolating the output signal from the chassis?

2. Do I need to isolate any of the following components from the chassis: RCA inputs, the binding posts, the on/off switch, and the volume pot?

3. Does it sound like I messed up the tubes? Can anyone interpret the audio sample?

-Kevin
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Old 25th November 2008, 07:53 PM   #3
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As you have already figured out, your binding posts need to be insulated from the metal chassis. The posts you have are typically used for loudspeakers, drilled and installed right thru the non-conducting wood speaker cabinet, thats why they have long posts and are un-insulated.

You can pick up some binding posts that are insulated and pop them into your metal chassis to solve that problem.

If your RCA input jack is not insulated, it can cause hum problems due to ground loops, but you should still hear reasonable output. The outer shell of the RCA should be tied to signal ground at one point, ie run a wire (preferably use coax wire with the shield soldered to your RCA shell and tied to your signal ground at one point, with the center conductor of the coax going to the center of the RCA jack). Since you want the signal ground connecting to chassis ground at one point, you should use insulated RCA jacks also. ie don't use the chassis as your signal ground wire.

The power input switch shouldn't be as much of an issue, as long as you tie the power cord ground wire to the metal chassis for good ground contact, typically with a ring lug, a #10 screw, and a star lockwasher on each side of the ring lug.

You can also use a wood (or other non-conductive material) insert with your existing binding posts as shown in the attachment.
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File Type: jpg huey22.jpg (88.6 KB, 411 views)
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Old 13th December 2008, 12:20 AM   #4
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I would also "clean up" all that wire that you have. Not only will it look neater, you'll have less chance of any interference that might be caused by excess wire. In my K-502 amp that I built (very similar to your amp) I used audio coax cable to wire my RCA jacks. I also ran my ground from the power cord to an insulated (from the metal chassis) terminal strip and then ran my ground from the circuit board to the same terminal strip. I built my amp on a Hammond aluminum chassis so I would not have any noise problems sometime possible with steel chassis. You can see pictures of my amp at the Yahoo Groups : singlendedtriodes.
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Old 15th December 2008, 06:03 PM   #5
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I forgot to add in my last post that I also grounded the chassis. The experts say that you should always ground the chassis in case there is a short.
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Old 15th December 2008, 09:49 PM   #6
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You should probably wire the tube sockets to the top side of the board, your wiring lengths are not conducive to stability if as I have interpreted you wired them to the bottom of the board.. (Much more wire required than necessary or desirable.)

Yes make sure you have your safety ground tied directly to chassis. The amplifier circuitry should only be grounded at one point to the chassis. (Read about how to avoid ground loops on this forum.)
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Old 14th June 2010, 05:27 PM   #7
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Has anyone tried other output trannies than the S5 supplied?
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Old 27th April 2011, 01:37 AM   #8
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Quote:
Originally Posted by Doug Kim View Post
Has anyone tried other output trannies than the S5 supplied?
I did some homework myself. I replaced the stock OPT with Hammond 1645: 5K, 30W.

Sound?
BASS BASS BASS ... there are lots and lots of bass compared to the stock OPT. Not the highest quality bass, but at least it is much better than before.
It seems the mid-high got slightly smoother, which is also good.

I put the whole amp in an enclosed aluminum chassis, with some side vent holes, but the amp gets super hot. I made chocolate fondue on the amp, and WAF got doubled. My wife said two thumbs up.
I need to punch more holes on the chassis.
But anyway, there is absolutely no hum after it is put in the chassis.

Doug
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