Another Simple SE builder

[Ty_Bower]

So, here's my thought for using the 6L6GA tubes. It basically involves switching out the C1 cap, which will give me a choke input power supply. If I believe PSUDII, I'd expect to get right around 450 volts with C1 in the circuit and about 305 volts without it.

Does anyone see any big problems with my idea? Am I going to end up with high voltage on traces too close together?

• Cut the trace marked with an 'X', between C1 and R2.
• Do not install R1.
• Do not install FREDs.
• Solder a short jumper wire (~ 4") at the end of the R1 pad which leads to C1.
• Attach other end of jumper wire to FRED solder pads leading to SW1-O2.
• Install SPST switch between SW1-O1 and SW1-O2.
• For a capacitor input power supply, attach the choke between L1-O1 and L1-O2. Close SW1.
• For a choke input power supply, attach the choke between L1-O1 and SW1-O1. Leave SW1 open.

[tubelab.com]

I think that your idea will work.

I have done a choke input Simple SE, but I did it differently. I used two chokes. The PC board was assembled according to the instructions. I cut the trace in the same location that you have marked. The board was then wired up normally including the choke and supplemental capacitor (if desired). The additional choke is added between the SW1-O1 terminal and the L1-O2 terminal. This puts the choke in the circuit where you just cut the trace. You can then wire a switch across the choke to disable it.

This allows the original CLC filter to remain in place and a LCLC filter to be used for choke input.

[Ty_Bower]

An even better idea. Would you think something like a Dynaco C354 would be enough? 1.5H, 55 ohms. They're cheap and relatively small. I be I could stuff one under the deck somewhere...

[Ty_Bower]

Hmm... playing with PSUD2, it seems the 1.5H choke might not be a good choice. It gives me lots of warnings about exceeding the rectifier's max PIV rating, and the output waveform looks weird (ugly). Nothing much less than 3H seems like a safe bet, especially if the load current drops a bit from the 140ish mA I'm pulling now. Probably something to do with that whole critical inductance thing.

I'm guessing right now that my best choice might be something like a Hammond 159S - 4H and 65 ohms. Sticking a NTC device (like a CL90) on the primary side of the PT might not be a bad idea, either.

[Ty_Bower]

So, while I sit and try to figure out my power supply options, I'm listening to Sheryl Crow on the Simple SE. It must sound good - the cat hasn't moved in the last hour...

[tubelab.com]

I was using a surplus 8H choke in my setup. The critical inductance requirement must be met for a choke input filter to work right. It is far better to have too much inductance than not enough. The Triad C-14X (6H 150 ohms) may work OK. It is cheap ($15) but UGLY, you need to hide it. I found some end bells from an old power transformer that fit after removing the mounting bracket.

The CL90 is a good thing and I have them in most of my amps. I have recently started using two of them one goes in series with the power transformer primary. This softens the initial surge caused by cold tube filaments. The second CL90 goes in series with the HV center tap. This makes life easier on the 5AR4 when it has to charge up some empty caps while it is still warming up. Recent new production 5AR4's seem to be a bit weak in this area.

[tubelab.com]

It must sound good - the cat hasn't moved in the last hour...

I loaned a Simple SE to a friend who normally listens to a multi gigawatt home theater system. He plays movies, MP3's and CD's. He connected the Simple SE in place of his front 2 channels amps. He was not impressed with the tube sound saying that it wasn't loud enough, and the thunder didn't come out right.

He did report a strange occurrence. When he played a movie that he had played multiple times before that contains a gunplay scene his cats ran from the room and hid. This did not happen with his big box rig.

[Evenharmonics]

Originally posted by tubelab.com
a gunplay scene his cats ran from the room and hid. This did not happen with his big box rig.

Must've been the even harmonics.

[hdlcx2]

I can't imagine someone not perfering tube sound to SS but then with movie soundtracks it could have something to do with DAC.

Anyway, thanks Ty for sharing your build with me. It's been a great ride so far.

[Davec113]

Ty, great you got it working. FWIW, I used switches for cfb and UL/triode, and far prefer triode with no cfb. UL sounds punchier at first, but the effect is tiring after some time. I am using the James OPTs and Omega XRS single driver speakers (93 dB sensitivity). I'm sure with your OPTs and speakers things will be different, but I've heard this from some others as well, so rigging up switches to compare might be a good idea. I'm keeping UL for when I want the power, but I will take cfb out of the circuit entirely.

Also, I'm using the new issue Tung Sol 6550 power tubes and am very impressed with their neutrality and soundstaging capabilities. The whole system just disappears.

I had some hum at first, but I used a short 12g wire to connect the Simple SE chassis to my preamp chassis, and this eliminated all but the faintest trace of noise.

Dave