stereo SE kt88 build ... abdellah diyaudioprojects design

[vaughn]

I'm sure others will chime in here but I can make a couple of comments

Your layout is ok but you want your laminations on the choke and the power transformer to be at right angles to each other to minimize hum. Personally, I would put the input jacks at the front of the chassis close to the first stage to avoid running the signal cabling through the power supply. I have built a few amps and preamps and the one thing I HATE is hum. Keep signal cabling short and shielded(shield tied to ground at source end to avoid ground loops). I know this isn't always as aesthetically pleasing as jacks on the back of the chassis but you are after great sound, right? I assume you will be using AC for the filaments; keep your filaments supply wires twisted and as compact as possible. You can even shield them but it is typically not necessary if you are neat. Heat shouldn't be an issue if your chassis is properly ventilated. I usually drill vent holes around the tube socket and place ventilation holes on the bottom plate under tubes to allow convection cooling.

I have been wanting to build another amp and this one is on my shortlist. I can't decide between a nice lower power push pull with 6BQ5's or the like or this amp.

 

[vaughn]

I also forgot to mention your output transformers laminations should be at right angles to the pt. You could also place them at an odd angle like Cary does on their amps but I think that you would have to actually wire it up and move them around to experiment with which location had the least hum. I have also heard that the laminations on output transformers should be at 180 degrees from each other, but I don't know if this is really necessary. I used the same James transformers on a 2A3 amp and the lamination direction isn't as obvious with a potted unit like these. The speaker terminals on the bottom should be on one side of the laminations and the primary connections on the other.

 

[jmillerdoc]

SMPS for filaments

I have had excellent results in using low cost SMPS for my filament power source. They are cheap and have very low ripple. I have picked them up on eBay for 12 dollars or so. Just a thought.
Jeff

 

[porkchop61]

I don't mean to hijack, I just was wondering if anyone has ever run 807 tubes in this design? I was thinking of making some adapters to go from octal to five pin sockets to try out this tube.
Is an 807 a good audio tube?

Glenn

 

[jmillerdoc]

400VDC Solen

Hi,
I was planning to use an 82uF Solen in parallel with 18uF more to equal the 100uF on the power supply. I have this giant cap laying around without anything to do with it and I wanted to use it here in place of the motor run cap suggested. The only problem is it is only rated for 400VDC, not 630 like I first thought. I know you usually want a bit of a margin but as you see I have zero. My question is.....do you think I should try it anyway? Is the worst case scenario a blown cap? Or worse? At this point I am planning to use it unless somebody here convinces me otherwise.

 

[jmillerdoc]

Another few questions....has anybody tried an Amperex 6DJ8 in place of the 6N1P?

I was planning on using the additional choke on the preamp tube supply, do you think one is enough for both sides of the tube or were 2 chokes used (5H). I happen to have one choke that will fit the bill if it is okay to use just one.

Man, this thing is going to be MASSIVE! I am laying it out on an 12x16 inch wooden chassis I built a while back, I think it will all fit but the thing is going to probably weigh in at about 40 pounds!

I picked up a Westinghouse 10H 0.2 amp choke to use here but the dang thing is giant and ugly. I think I am going to raise the heigth of my chassis on the back and tuck this thing underneath the surface of the amp.

Additionally, I really don't like the idea of having my inputs on the front of the amp, any good tips on shielding so I can assure I don't pick up any noise on the way from the rear RCA inputs to the preamp tube (which will be mounted upfront and center) I have some bery nice shielded cable I was planning on using with the shield connected from only one end to earth main. Any additional ideas on this?

Thanks,
Jeff

 

[Zekk]

LED bias for 6N1P?

Wavebourn .. pardon me if I may ask you how to wire up a series of LED in place of the 1K/100uf used in the cathode bypass? I'm a newbie!

Your suggestion to use 24K on plate and 360R for cathode is GREAT!
Despite the reduced gain, no problem with my 604E's 101db, sounds sweeter with deeper bass.

Thanks!

Zekk

 

[PhilippeS]

Hi,

read in a french forum :

"Russian 6N1P is not equivalent to the 6DJ8 !! The equivalent is the 6N23P,
6N1P is rather a ECC180…
The Chinese 6N1 is well a 6DJ8 but nothing to do with a Russian 6N1P !! "

Philippe

 

[revintage]

This might give you guys the answer of what a russian 6N1P is:

Tube Tester Files - 6N1P - 6H1?

Also great to work out your loadlines from.

 

[PhilippeS]

Thank you Revintage,

on your site the operating point

6N1P : Va 250V, Vg -4.5, Ia 8ma, Gm 4.7 ma/V

6N23P : Va 100, Vg -1, Ia 15ma, Gm 10.6 ma/V.

6DJ8 : Va 90, Vg -1.3, Ia 15ma, Gm 12.5 ma/V.

I'm not a technician, but I'd never replace a 6DJ8 by a 6N1P.

Philippe

 

[revintage]

on your site the operating point

Hey Phillipe,

Nikolas site is great!

I´d absolutely replace the 6N1P with a 6DJ8/6N23 if we go from the measurements. But one have to redesign the circuit to suit them.

 

[revintage]

If we go by Nicolas curves, a Rk of 470ohm(-75/+80V swing/5mA) would be far better than the 1k in the original.

 

[PhilippeS]

Sorry for the confusion (and my poor english), I meant "the site you talk about.

Thanks for "redesign the circuit to suit them."

Philippe

 

[jmillerdoc]

The original design and schematics I found for this amp at diyaudioprojects.com has a line at the bottom of the page where the builder preferred a 6DJ8 Amprerex Bugle Boy tube. I presume it must work in this amp because of the authors comments.
Thanks,
Jeff

 

[88man]

Do you have to use polarized electrolytics for bypass caps for the 100uF/25V and 220uF/63V values?...

Can you use non-polar MKP capacitor instead, like Mundorf MKP Supreme, Auricaps, or Clarity PX, or Solen Fast Caps without degradation?...

I can't find values for Black Gate caps since they've been long out of production. Any advice on top tier alternatives?...

 

[jmillerdoc]

I like Elna Cerafine, large selection at Partsconnexion. Also Nichicon KZ Muse does well too. Check out the above vendor, lots of nice stuff there.

 

[jmillerdoc]

Chassis ready to go

Here is a sloppy pic from an Iphone of my chassis, ready to go. I will try to post some better pics later when I have access to my camera. The wood from bottom to top is Cedar, Canary, Rosewood, Canary, Madera, and Oak. You can see my hugh, ugly, 200mA 10H Westinghouse choke mounted up underneath. I just got all of the parts in a couple of days ago, should have her together in a week or so.
Jeff

 

[jmillerdoc]

So if I wanted to use my 6DJ8, what changes would you reccommend in the circuit?

 

[revintage]

Just adjust Rk to get between 120 and 150V Ua. Probably in the ballpark of 500ohms.

 

[88man]

Thanks Jeff for suggesting the Elna-Cerafine and the Nichicon KZ Muse caps. I'll try Partsconnexion. I've heard the Elna-Cerafines have 98% of the sonic attribuites of the Black Gates. I wonder how they measured that, but it seems good enough!... Oh, hey I see you've put the cart before the horse, but the enclosure looks distinctive.