stereo SE kt88 build ... abdellah diyaudioprojects design

[scitizen17]

Originally Posted by alexg

Actually, if you use 5ar4 for the rectifier, you don't need a standby switch, The B+ will ramp up slowly and will give your tubes to warm up before the full B+ is applied.

You can also make some soft start devices for slow ramp up of B+.

HTH.

When using the Hammond 374BX the 5AR4 provides 450V B+ according to PSUD2. Also the rectifier goes over-current on startup.

Can you enlighten me as to the "soft start devices" of which you speak?

[alexg]

Originally Posted by 88man

Alexg, have you tried the amp without the LC circuit to the driver plate? Can I use a choke with 26R?

Thanks!

Actually, you don't need the LC on the driver stage, an RC with 100R and 47uf should work fine.

[alexg]

Originally Posted by scitizen17

When using the Hammond 374BX the 5AR4 provides 450V B+ according to PSUD2. Also the rectifier goes over-current on startup.

Can you enlighten me as to the "soft start devices" of which you speak?

There are some circuits published on the internet that allows for soft start (slow ramp up of B+) for tube circuits. Some can be bought ready to use.

[porkchop61]

Originally Posted by alexg

Actually, you don't need the LC on the driver stage, an RC with 100R and 47uf should work fine.

I'm running mine without this extra filter on the 6N1P plate, and I don't have any audible noise. I'm just curious if it's worth putting this setup in my build (I'd also just do an RC filter).
I guess it's just cheap insurance to just add this to the circuit.

[scitizen17]

Originally Posted by porkchop61

I'm running mine without this extra filter on the 6N1P plate, and I don't have any audible noise. I'm just curious if it's worth putting this setup in my build (I'd also just do an RC filter).
I guess it's just cheap insurance to just add this to the circuit.

I am going to use the LC plate filter on my build. I've just about got all the components, and my circuit layout is complete on paper. I'll let you know what the outcome is after I put the scope to it and give it a good listening session.

[scitizen17]

Originally Posted by alexg

There are some circuits published on the internet that allows for soft start (slow ramp up of B+) for tube circuits. Some can be bought ready to use.

Thanks alexg, I found several by searching. The most effective circuit I came across is much simpler than I could even imagine, and cheap too.

[jmillerdoc]

Here are a few fairly low res pics taken of my nearly completed KT88SE amp. A few things done differently is the power supply which I have modeled on PSUD2 to be right at the border of maximal operation of the 5U4-G tube. It uses a combination of Solen and ASC oil caps. The arrangement is a 25uf Solen -> 20R -> 47uF Solen -> 10H 77R DCR Wesinghouse choke -> 80uF ASC coupled parallel to an 82Uf Solen -> B+ tap -> 20R Wire wound -> 15uF Solen -> driver tap. The tube complement is a set of Mc Intosh KT88's and 6N1P Russians. The Coupling caps are 0.33 Jupiter Beeswax and tinfoil, All resistors are PRP or Mills (a couple of Xicon WW in the PSU), and Blackgate bypass caps. All wire used is silver stranded with some home built shielded cables to the RCA inputs and from a blue velvet pot to the driver tubes (white cotton covered cables). The power and OPT's are of course Edcor.
The Chassis is all hand-built from exotic woods including Rosewood, Madeira, Canary, red Cedar, and some oak. Binders and RCA's are topline Vampire's. Most of the passives were sourced from Soniccraft.com. The remainder of the parts were gathered from here and there like tubedepot.com and tubesandmore.com.

I need to finish the filament wiring which I decided to rectify and filter. I have 2 small modules with the rectifiers and filter caps not shown that will go on the opposite side of the large Westinghouse choke from the Solens seen on the right of the choke. power input is a simple filtered IEC jack bought at Jameco if I remember correctly.

I haven't powered it up yet and will likely have to make some adjustments to the power supply filter when I do. I find PSUD2 to be off every time I have used it but not by much. Once I am done I will try to supply some scope traces on it for ya.
Jeff Miller
Lawton, OK

[jmillerdoc]

Also, on the top of the amp, in front of the rectifier tube you will see a toggle switch and a rotary knob. The toggle switches the 3K into parallel with the 560R cathode resistors on the KT88's to change the current for the EL34 and 6L6 tubes. Also, the rotary knob switches between UL, Triode, and Pentode operations.
Jeff

[scitizen17]

That is a work of art, very nice. I certainly hope it sounds as good as it looks. Now you've got me really psyched to finish mine. Can't wait to get the full report!

Scott

Originally Posted by jmillerdoc

Also, on the top of the amp, in front of the rectifier tube you will see a toggle switch and a rotary knob. The toggle switches the 3K into parallel with the 560R cathode resistors on the KT88's to change the current for the EL34 and 6L6 tubes. Also, the rotary knob switches between UL, Triode, and Pentode operations.
Jeff

[88man]

Jeff, don't keep us in suspense any longer - plug that baby in! Seriously, I am curious on your take on the sound. I see that your layout is different than Glen's or Alex's - but esthetically it looks balanced. I really like it!

A safety question: While handling and testing ASC caps in PSU, how do I bleed the charge safely and completely to prevent an accidental shock?... Do I use a 5kR across the terminals??...

Thanks!