My latest project - KT88 SE tube amp

[greywarden]

Re: My latest project - KT88 SE tube amp

They say that the twisted pairs of AC wiring helps filter/cancel out, etc some RF/EMI stuff...

[TN Allen]

Re: My latest project - KT88 SE tube amp

Want to see the underside of my amp?

Just curious, what is this amp?

[PWR RYD]

Re: My latest project - KT88 SE tube amp

Grey is correct. It is a good practice to tightly twist the AC lines so their fields' cancel. It is actually only important where those AC lines are going to be in close proximity to the low level signal wires. The two green wires twisted together are the 6.3 VAC wires that will eventually head over to the three tubes to power their filament heaters. Since they are very close to the low level audio lines their twist will help eliminate that dreadful 60 Hz hum. The rest of the wires that I have twisted (red HT wires, the black 120VAC wires, and the yellow 5V recitifer wires) don't really need to be twisted. They are all over on the power supply side of the amp and never run anywhere close to anything sensitive. I like to twist them, however, because it doesn't hurt anything and I think it helps keep things neat and tidy. I've done this on my other builds (tube and class D) and all of those are very quite.

And Grey is also correct, I just use my cordless drill to carefully twist the wires.

[PWR RYD]

Re: My latest project - KT88 SE tube amp

Just curious, what is this amp?

That is his Tube Labs K-12 amp kit. I think he posted a top side picture on the first page of this thread.

[TN Allen]

Re: My latest project - KT88 SE tube amp

That is his Tube Labs K-12 amp kit. I think he posted a top side picture on the first page of this thread.

Thank you, I remember it now.

[PWR RYD]

Re: My latest project - KT88 SE tube amp

Finished the filament wiring. That is the last of that silly twisted wiring

[Psycoacoustics]

Re: My latest project - KT88 SE tube amp

I just now noticed you are from Willowbrook! We should get together and listen to some speakers and amps.

I'd love that! However, right now it looks like I won't get a day off till Indiyana. Are you going?

[Pete Schumacher]

Re: My latest project - KT88 SE tube amp

Just out of curiosity, but why don't these designers dump the 6.3VAC and instead, rectify and send DC to the filaments?

[PWR RYD]

Re: My latest project - KT88 SE tube amp

Hi Pete,

I'm no expert but I've read a little bit on that exact subject. Generally people feel that the extra parts for DC are not necessary. Good wiring techniques take care of it. It might also be that a lot of tube amp fans like "strickly tubes only" (i.e. no semiconductors) and rectifying the filament supply with only tube technology is a fair bit of more work. I know that Bruce Heran of Oddwatt likes to use 12VDC laptop SMPS bricks for his heaters. That makes pretty good sense.

[TN Allen]

Re: My latest project - KT88 SE tube amp

I'm curious about the volume control you're using, I assume it's for volume, is it an attenuator or a potentiometer?

[PWR RYD]

Re: My latest project - KT88 SE tube amp

It's an Alpha audio tapered (logrithmic) stereo potentiometer. It simply attenuates the input line level signal to control output volume. One of these days I will purchace an Alps pot. But so far I haven't had any issues with the Alpha units. It's 100Kohm.

[PWR RYD]

Re: My latest project - KT88 SE tube amp

I got the big B+ inductor (CLC filter) mounted, as well as the smaller 5 Henry inductor for the driver LC stage:



Work on this project is going to slow down just a little bit as my real (career) work is going to be super busy for the next week or so. Not to mention the output transformers haven't shipped yet.

[greywarden]

Re: My latest project - KT88 SE tube amp

Every time I see a tube amp build that's done well like this one, I wonder if someone's going to pick it up off a stranger's yard sale table for $5 and clean it up and fix it and play whatever music is popular 100 years from now through it haha. Maybe now 100 years, but a while down the road, you know

[TN Allen]

Re: My latest project - KT88 SE tube amp

Thank you for the potentiometer info. Also for the step by step descriptions and photos. I'm learning quite a bit that I have not understood previously, despite several amp and preamp projects, which have turned out more or less well, despite ignorance of the way circuits work. You are providing a wonderful opportunity for understanding practical tube amp construction, especially in that others are contributing additional info.

[TN Allen]

Re: My latest project - KT88 SE tube amp

"Every time I see a tube amp build that's done well like this one, I wonder if someone's going to pick it up off a stranger's yard sale table for $5 and clean it up and fix it and play whatever music is popular 100 years from now through it haha."


Given the quickness of technological change over the previous few decades the following is probably very unlikely, who knows how people will listen to music in 100 years, but it could be that yard sale will also include music contemporary to the amp., perhaps even 100 years earlier. Perhaps the fortunate purchaser will buy the amp and the music, and not only play what is popular at the time of purchase, but the earlier finds as well. He or she may enjoy the music, and a little insight (perhaps imagined and unrealistic) into March 2013.