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Metal Legs 2nd November 2008 12:14 AM

Built an amp kit!
Hi everyone.

Last week I finished building a couple of k-501 monoblock tube amp kits from Antique Electronics Supply. I fought a noise problem on one channel for a while. Turns out it was a bad solder joint on the tiny 4-leg rectifer. Once I resoldered it there was no noise, except for what you normally hear when you mute the input and crank the pots way up. I'm looking at enclosure options right now, but the amps are working. The pine boards they include for mounting seem quite inappropriate--unless your amp is for a science fair or something.

This project took over my mind for two evenings like I was plugged into the matrix. I don't remember the last time I was this posessed by a project. I've built a few amps before, but this is my first tube amp. I'm trying not think about modifications...

My initial untrained and very humble listening impressions so far:

Even with the cheap old speakers I used for testing, the sound impressed me. I know this is totally subjective but it does indeed sound "clean" and "smooth". The midrange is very warm. I was most impressed by the definition and tightness of the low
frequencies. On one occasion I even said to myself, "what is that weird noise--is something wrong with the amp?" and then realized it was just part of the bass guitar track that I never heard before. I also noticed that the sound seems less "directional"--like you can't tell exactly where the instruments are coming from.

So far I'm impressed and happy with my purchase. I'll definitely find a suitable enclosure for it. I took a bunch of pictures of the building process if anyone wants to see them.

Metal Legs

gni 2nd November 2008 01:25 AM

Bring them on. . . I was going to install a kit tub amp
into the shell of my old Yamaha M-45.

roggom 2nd November 2008 02:27 PM

Some chassis can get expensive, I have lucked out and found PA paging amp like the Toa BG-130 for a few dollars in the pawns. They have lots of room inside and cord, fuse, switch etc. and has vented top.

Richard Ellis 2nd November 2008 02:44 PM

Congrats 'Metal legs' on your completed project......So what 'cheapie' speakers are you running??
The world is your oyster as to how your amp is going to look like.....From the plain vanilla "Black death" ( All audio gear is black) the retro style, you have an open book designing the chassis.
Look thru all the photos in the gallery.......I'm sure there is something that will peak your artistic interest.
_________________________________________________R ick.....

Jeb-D. 2nd November 2008 06:08 PM

You defiantly should put it (or them, if you got a pair) in a chassis eventually. Also, be careful when working on it, because those caps will hold a charge long after power is removed. It's a good idea to install a bleeder resistor across the main reservoir cap. I used 100K 2W, tacked on the bottom side of the board across the cap terminals.

I went for the vintage look with mine and used the chassis pictured below. It was $17 from surplus sales of Nebraska. I had front panel express machine the front and back panels (plenty of vent holes in the panels of course). If you have two of the k501's, both would defiantly fit in one of these. It may be a little over sized if your only running mono

Richard Ellis 2nd November 2008 07:09 PM

OK...Oak Box...How about a smoked Lexan acrylic (Sp?) panel for the front Two 105 mm holes toward the rear, the main Output tubes on top, The Illumination at night would look great (Perhaps a blue tinting?
The Pre tubes would illuminate the inside.
__________________________________________Rick.... .......

Jeb-D. 2nd November 2008 11:57 PM

My front and rear panels are aluminum with a large cutout with clear vented plexi-glass windows. The k50x amplifier will fit all tubes within.

Metal Legs 3rd November 2008 12:42 AM

2 Attachment(s)
Hey guys (and gals?)

Here's a picture of the amp up and running. Incidentally I do notice that it is picking up/amplifying a small amount of RF noise--particularly at night. Not surprising, I know, all spread out like this.

The speakers are 5 watt 2-way 3.2 ohm junkers. Salvaged them from a boom box (a "Sharp") which quit working about 15 years ago. I'm not using them now, of course. I used them for the initial "smoke test"--you know, the "power-on" test after you finish soldering the last component, where you keep one hand on the power cord and watch and smell very closely.

Soonerorlater 21st November 2009 09:18 PM

Hi Metal legs,
Nice picture, always wanted to see what the K501 pcb looked like. I see that you've mounted most of your components underneath.


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