s5electroniscs k12m Tube amp

[aculous]

I don't what the heck I did wrong but here goes.

I bought the amp and promptly yanked out the blue lead on one of the output transformers. Yea didn't know how delicate they were but I was trying to strip it with a knife instead of the auto wirestripper I have which I was too lazy to go get. So 60$ later or whatever the sum of money was I bought two Hammond audio output transformers as per a mod that I saw online. Well they have additional leads that I was not familiar with because I am an idiot when it comes to EE so I just kinda matched up the colors as they were on the original transformers.

Plugged it in and lit the suckers up. Looked cool...so I did the moment of truth and put my Teac DAC/cd player on there and put in a herbie hancock cd and turned it on. Well thinking I was not going to get any music until I actually plugged in the speakers...I was a little amazed that at full volume I could hear the piece being played....I'm guessing through the tubes...


any ideas? I think I have a serious grounding problem. Or maybe I should just box it up and have someone with electrical talent take care of it. But I figured I would ask everyone first and see what you think.

Pictures to come

[Saurav]

Well they have additional leads that I was not familiar with because I am an idiot when it comes to EE so I just kinda matched up the colors as they were on the original transformers.

You're a brave man

You should be able to find specs on the transformers your purchased. 2 of the leads will be the input, the others are probably outputs at different impedances. The O/P transformers I've used have a common ground, a 4 ohm tap and an 8 ohm tap. The Hammond website should tell you which color wire does what.

It might be a little difficult getting the same information for the stock transformers. You might be able to figure it out by following the wiring in your amp, but that would probably take some electronics experience and some luck

I don't know, maybe there's a coloring convention when it comes to output transformer wires, and you might have gotten lucky and wired it up right.

Well thinking I was not going to get any music until I actually plugged in the speakers...I was a little amazed that at full volume I could hear the piece being played....I'm guessing through the tubes...

That might be normal, some tubes are microphonic and 'sing' at high output levels.

any ideas? I think I have a serious grounding problem

So did you connect it to speakers? Do you get any output? Is there a hum/buzz? What makes you think you have a grounding problem?

Or maybe I should just box it up and have someone with electrical talent take care of it.

Probably a good idea. There are voltages inside the amp that could maybe kill you, or at least cause you a good deal of discomfort. You could have damaged some of the other components in your amp if you hooked up the new transformer incorrectly.

[aculous]

...well

ok well to answer some questions.

yes I connected a speaker and am getting some serious buzz and barely any output. (kinda expected that, the speakers I was using was not ridiculously sensitive and probably in the 85db range)

the grounding idea is because well I guess I was not used to the microphonics, that and the fact that the directions are really vague on grounding. I mean thew grounding points are not labeled or shown and moreover....its a wooden plank.....how do you ground a wooden plank...

And as far as voltages killing me...yes there is a distinct possibility of that but I am pretty sure i'll be ok. I have been shocked with 240 before....which should have technically killed me....(amperage wise really) So brave or stupid you be the judge.

disconnected one of the grounding points that I don't think I was supposed to hook up. The main power transformer that is. I have pictures. I know its ridiculously messy, but calm down I am in R&D at the moment.

[Saurav]

I have been shocked with 240 before

I've wondered why my amp was tingling, and then realized I hadn't unplugged it, so I was touching the 120V coming in from the wall. So, yeah, I'm as brave/stupid as you Having said that, my amp has 600V inside it. I haven't looked up the tubes in your amp so I don't know what B+ voltage they need, but I just wanted to point out that it could be higher than the supply voltage.

I'm not really sure what you're showing with these pictures, so I can't really help you there. There should be specific points in the circuit that need to be grounded - in the power supply section it should connect back to the earth prong in the AC input, while in the audio sections, it should connect to the shield of the RCA input.

I've built a tube preamp kit from Bottlehead when I had practically no idea what I was doing, and I was successful because the instructions were so explicit that anyone could follow them. Specifically, they had a long series of resistance checks between multiple points in the schematic before you even powered them on. Then I think it asked you to plug in the AC power, but no tubes, and then do a bunch of voltage checks. Turn off, add the tubes, turn on again, more voltage checks. Only after you passed all those did you connect source/amp and try to listen to music.

I'm assuming your instructions aren't that clear. That would make troubleshooting your amp a little complicated. I'd suggest finding someone who knows how to look at a schematic, compare it to the circuit, and run some tests to try and figure out what might be wrong.

[Hdale85]

Why not get a real chassis to put it in and work on grounding it there? You should be able to tell pretty easily where the grounding points are either by the schematic or even just looking on the PCB.

[aculous]

that would make sense except that its not labeled at all and rather vague on the PCB and I have little to no knowledge on schematics. I'm gonna get a little quick reference guide today to read some of the symbols.

[JoshK]

Your wiring is the cause of your buzzing almost certainly. AC wiring must not run closely with DC wiring inside a tube amp and if they cross they should be crossed at 90º. AC wiring, such as heaters and power entry should be tightly twisted and run along the perimeter of the chassis and only to the tube in the shortest distance from the edge of the chassis and then back to the perimeter to go to the next tube, not directly from one tube to the next (unless they are very close together).

Wiring neatly will reduce a great deal of hum, good grounding practice will do the rest. However, I fear that given your admitted lack of knowledge about the technical details, happening unto good grounding would be a bit of a miracle. Does the kit come with instructions on how to run grounding?

Hammond transformer wiring schematics are available online and easy to find with searches. I humbly suggest you look yours up and determine that you wired it correctly. Not wiring it correctly can destroy your amp and maybe even your output transformers. I can help if you provide me with the necessary info.

I really do suggest you wire it neatly first, as hum pick-up can be many volts worth and take the tubes so far out of bias as to not operate correctly. This alone can explain why you are getting buzz and little music.