My latest project - KT88 SE tube amp

[PWR RYD]

Re: My latest project - KT88 SE tube amp

I was able to sling a little more solder after work tonight. One really cool thing about scratch building an amp and doing point-to-point wiring is that aside from basic safety rules... anything goes. You can lay things out however you like. The other big advantage vs. a printed circuit board is that you get to work in 3-D. So by careful planning or simple trial and error or dumb luck you can create significant space between signal carrying conductors/components. Here are a few shots of tonights progress:

[AJ]

Re: My latest project - KT88 SE tube amp

Nice work!

I've done enough point to point stuff to know that a well designed PCB is really nice in it's convenience, but for an amp like this PtP does end up looking pretty neat.

[PWR RYD]

Re: My latest project - KT88 SE tube amp

Slung some more solder after a very difficult day at work :(

Anyway, here are few shots of the output tubes' cathode resistor and capacitor:







As seen, there are separate ground wires from each RC back to the common signal ground bus. Also the loopy arc of the white wires from the RC to the tube sockets might not look the neatest, but it keeps signal wires well away from the AC filament wires.

[JasonP]

Re: My latest project - KT88 SE tube amp

The underside of your DIY amp here is a thing of beauty. I'm impressed the more I see. Good job man, good job. *kicks his horrible looking Sure T-Amp build for being too ugly*

[greywarden]

Re: My latest project - KT88 SE tube amp

Wow it's looking amazing, I wish I had the patience to build something like this! haha

[[email protected]]

Re: My latest project - KT88 SE tube amp

I'm glad one of us has an idea what your doing. it deserves a glass bottom.

[Pete Schumacher]

Re: My latest project - KT88 SE tube amp

I recently worked on a 40W SET that had an electrolytic cap in the cathode that bypassed the resistor, as you're showing there. We had some noise issues that were dogging us, and one of the things we did was replace that cap with a film type, and the noise issues were greatly diminished. You might want to bypass that electrolytic with a nice Dayton poly.

[blair]

Re: My latest project - KT88 SE tube amp

Pete's right about the bypass cap. You see film bypass caps bypassing the bypass cap all the time. You don't want to bypass that step by bypassing the option and having noise from not bypassing the bypass cap.

Or, just flip your switch and use the green LED CCS. What's up with the dual bias setup and the switch? Kind of cool.

[WernerM]

Re: My latest project - KT88 SE tube amp

Pete's right about the bypass cap. You see film bypass caps bypassing the bypass cap all the time. You don't want to bypass that step by bypassing the option and having noise from not bypassing the bypass cap.

Or, just flip your switch and use the green LED CCS. What's up with the dual bias setup and the switch? Kind of cool.

LOL that is funny...

In all seriousness though, wouldn't you want to remove the electrlytic completely if you are replacing it with a poly? Wouldn't trying to bypass it by adding another (poly) cap of the same value effectively double the capacitance value at that point since they are in parallel?

[AJ]

Re: My latest project - KT88 SE tube amp

LOL that is funny...

In all seriousness though, wouldn't you want to remove the electrlytic completely if you are replacing it with a poly? Wouldn't trying to bypass it by adding another (poly) cap of the same value effectively double the capacitance value at that point since they are in parallel?

Uping the value won't make much of a difference. The low end frequency response is going to be dominated by the output transformer anyway, and I think Pete was talking about bypassing the electrolytic with smaller value film cap. I'd say 5uf to 20uf. A 220uF film cap is huge.

[blair]

Re: My latest project - KT88 SE tube amp

Most of the time I am reading through schematics, they use 1-5uf and another .1uf or so. The .1 is a bit overkill IMO unless you keep your scope on and just listen to sine waves for visual effect

Adding the 1-5 uf will help, and you have to have some. Heck, your a speaker builder;)

Blair

[PWR RYD]

Re: My latest project - KT88 SE tube amp

I'm going to first build it with just the 220 uF electrolytic and listen to it for a while. Adding a small film bypass cap will be super easy and I have plenty in my stock. Should be interesting.

[Psycoacoustics]

Re: My latest project - KT88 SE tube amp

Dude,,,, you are sick! Your ADHD is way out of control!:D The yellow shrink tubing between those resistors?,,, And the white wire proves it!

Hey,,,, when your done with that one ya wanna build me one?

Once again,,, Beautiful job!

[PWR RYD]

Re: My latest project - KT88 SE tube amp

A little more stress relief after a long day with lots of windshield time. Nothing much to say other than I'm down to just doing the input shielded wiring lines and the output transformer wiring (they'll be here Monday!!!! )







Oh yeah, I guess I can comment a little bit about the two toggle switches. The one closest to the driver tube (front of the amp) allows me to quickly switch the cathode bias between an RC network or the two LED's. Some people have said that the LED bias sounds more detailed. The toggle switch closer to the output transformers allows me to switch between Ultra Linear Mode and Triode Mode. This is the first SET (Single Ended Tube) amp I have ever built... so I don't know what I will like best. The UL mode produces about twice the power (~10 wpc) whereas the Triode mode produces about 5 wpc. From what I have read many people greatly prefer the lower powered Triode mode. Totally don't know... I'll have to hear for myself

[greywarden]

Re: My latest project - KT88 SE tube amp

Oh wow, that's pretty nifty! I imagine you'll initially like the UL mode, because of the extra power and eventually settle on what you actually like best, haha.

What speakers and setup is this going with?