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planning DIY SE KT88 build

I had mine wired up as an integrated (with cheap Alpha volume pot). I left it wired in, even though I built a Forewatt preamp. Decided to remove the pot and I think it really made a big improvement.

It was all Paul Simon tonight with EH 6CA7 tubes. "There Goes Rhymin' Simon" & One-Trick Pony. My first listen to these. It blew my mind. What superb recordings and great original songs.

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invaderzim said:
It is funny that you ask about the 5U4GBEH; I kept thinking that I should research the sound it makes at startup. I guess that is just what they do.
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I am going to switch my rectifier to a Sovtek 5AR4 that I have. It is smaller, dead quiet and very gradually brings up the voltage. The 5U4GB jingles and hisses constantly & it spikes to 575 V or so immediately, then drops down when the tubes warm up (?)

The only issue is that the 5AR4 will give about 30 more volts or so. You'd have to drop some voltage.
 
invaderzim said:
I'm trying to decide between an aluminum chassis and a steel one (both Hammond ones). The aluminum would be easier to work with but I like that the steel one comes in black so I don't need to try to paint it. Just curious if I'd likely really regret going for the steel when it comes to drilling.

Also, thank you for the picture of your setup. I was planning my layout in a somewhat stupid setup for appearance with the power transformer in the middle but after looking at your layout it hit me that it is much wiser to keep the power to one side and the signal to the other as much as possible.
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It is not much harder to drill steel you just need to start a pilot hole with a small bit. I like a steel chassis a little more because steel is stronger per similar thickness. Also steel takes paint better than Abluminum.
I have found that layout can be very diverse without compromising the sound quality. But one must definitely use a ground bus or a star ground to keep the amp quiet. Wherever you decide to put your power trans just try to keep all the AC carrying wires neatly arranged from there and the signal wires away from that. Easy peasy, good luck
 
Stumper1 said:
So.... Just put the 2 OT's , 1 PT and Choke into the shopping cart at Edcor. Shipping charges range from $57 (UPS and FedEx) to $103 (USPS Priority Mail)!!!!! Yikes!

Is this typical with Edcor??
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You should talk to a person at Edcor as the shopping cart probably added up the shipping costs per each transformer. I just ordered some OPTs a few months back and I could not be happier with their performance or appearance. It took them 3 weeks to ship them to my door. I ask them about the shipping and apparently, they had complaints about "combined" shipping so on USPS they ship the transformers 1 to a box. That sucks but still their price is very competitive.
I like the idea of having them make me a fresh transformer when I order it.
 
jdsalinger said:
I am going to switch my rectifier to a Sovtek 5AR4 that I have. It is smaller, dead quiet and very gradually brings up the voltage. The 5U4GB jingles and hisses constantly & it spikes to 575 V or so immediately, then drops down when the tubes warm up (?)

The only issue is that the 5AR4 will give about 30 more volts or so. You'd have to drop some voltage.
Click to expand...

What about going with a classic 5U4G?

Now I just have to resist the urge to try more different capacitors; that could get expensive fast.
 
Now that everything has had time to settle in, and I had a chance to go completely crazy and get a pair of Mundorf Silver Oil capacitors for it, I completely love this amp. It is so crazy good for being a pretty simple setup. It runs circles around the Marantz $1,700.00 amp that I returned before starting on this build.
I get no noise or hum at all between music and the music itself comes through so clear.

I wish I'd built it years ago.

Thanks again to everyone for their help, advise and tips on this project!
 
How do the Mundorf compare to the Auricaps and Russian PIOs?

Care to share a pic of the innards? :)
 
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I just ordered some 0.33uF Jantzen Superior Z caps
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These will replace my 0.22 KimberKaps. I have the Superior Z caps in my preamp.
 
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jdsalinger said:
How do the Mundorf compare to the Auricaps and Russian PIOs?

Care to share a pic of the innards? :)
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It is probably impossible for me to give an objective review of them. It is so easy to imagine improvements in something that is so subjective. Knowing the cost it could simply be unconscious self defense of the purchase to think they sound better. That being said they seem to be a good mix of the Auricaps and the Russian characteristics.
The detail seems quite good with sounds that should be crisp sounding crisp while still sounding smooth overall. My old, not so good quality pop music isn't as harsh as it was with the Auricaps and is more listenable, while the different instruments in better jazz type recordings stand out more. The bass seems fuller. I find myself listening to the amp more and often louder than before.

I still have to try to get the pictures of the underside off the old blackberry tablet in the garage and see if they aren't too embarrassing for the wiring.

jdsalinger said:
I just ordered some 0.33uF Jantzen Superior Z caps

These will replace my 0.22 KimberKaps. I have the Superior Z caps in my preamp.
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Nice, what will going to .33 change for the sound?
 
invaderzim said:
Nice, what will going to .33 change for the sound?
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Seriously though, a few other builders have tried it and I've even read some recommendations, so I thought I'd give it a go. Probably not noticeable though. It will lower the -3dB point slightly.
 
Well, I'm done. :music:

These Jantzen Superior Z caps are the cat's pajamas! I have 2 way horn speakers & now when I listen to a saxophone, it sounds like the horn IS the saxophone. It just couldn't be much more realistic.

Another big difference is the intimacy & realism of brushes on a snare drum. I couldn't believe how "iin the room" it sounded. On one song, the snare sounded like it was sitting in the place of my left speaker...but then the sax came in and was hovering in the middle of the room. wow.

Familiar songs truly sound new because there is so much information that I never noticed before.

Sound stage didn't seem to be wider, but deeper. Most of the music I have listened to has been small jazz groups, so the venues or studios are smaller.
Some Beach Boys tunes had that nice reverb or concert hall effect though.

I don't think the .33uF vs. .22uF had any noticeable difference, but Superior Z are definitely superior to KimberKaps. And for $5 more per cap, they are pretty much 150% to 200% the sound quality of the KimberKap.

I read one review of the superior Z that said the mids are "dry", but I didn't find them to be. Midrange is really smooth and musical. I used to not care for mid-range and EQ'd my system to drop it. After I built my KT88 power amp, I realized that it sounded a tad forward, but more delicate and detailed without tone controls. My ears grew accustomed to the sound, so I designed my preamp without controls too. But now, these caps absolutely erased any thought of needing tone controls. Every frequency band is enjoyable and well balanced.

They sounded congested and peaky for the first hour, but after about 2-4 hours they were broken in. I have about 10 hours on them now.

Best $25 I've spent on mods.
 
jdsalinger said:
I got 442V B+ with my XPWR-222 Edcor power transformer (375-0-375). I added a 100ohm 10W power resistor right after the 10H choke and now I'm getting 406V B+ with the 5U4GB.
You could also probably put it between the 10uF and 100uF filter caps too.
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Hello,
I realize this is an older post but I've been reading up on this build and preparing an equipment list as well. I noticed that you're using the XPWR-222 (375-0-375) which is a bit more output than what was shown in the original schematic (350-0-350). Was this intentional or did you simply already have this available. I think the original call for a Hammond 273BX which is rated at 115 input with (350-0-350) out. I also noticed that all of the possible EDCOR alternates are rated assuming a 120 VAC input. Just curious.

Thanks,
 
Intentional. There were other KT88 projects like this one http://diyaudioprojects.com/Tubes/KT88/ that call for a 750V CT power transformer. I figured it was safe. You'll be OK with 700V CT too.
There are several other builders who actually use a much higher B+ than 400V ( 440 or 450 maybe?), so you're safe and probably wouldn't even need to add the power resistor like I did.

I chose the XPWR-222 for it's 350mA rating (way overkill, but not much more expensive). The Edcor that others were using seemed a bit low to me (175 mA I think?). The Hammond is 201mA and will be fine if that is what you use. Secondly I chose the 222 because it didn't have the un-necessary 240VAC primary. Simple as that.
 
jdsalinger said:
Intentional. There were other KT88 projects like this one http://diyaudioprojects.com/Tubes/KT88/ that call for a 750V CT power transformer. I figured it was safe. You'll be OK with 700V CT too.
There are several other builders who actually use a much higher B+ than 400V ( 440 or 450 maybe?), so you're safe and probably wouldn't even need to add the power resistor like I did.

I chose the XPWR-222 for it's 350mA rating (way overkill, but not much more expensive). The Edcor that others were using seemed a bit low to me (175 mA I think?). The Hammond is 201mA and will be fine if that is what you use. Secondly I chose the 222 because it didn't have the un-necessary 240VAC primary. Simple as that.
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Thanks very much for that explanation. I'm considering the EDCOR XPWR155. It's rated at 200mA and should to the job nicely.

Again, thanks!
 
I know I bitched about Edcor shipping before but... After flip flopping over a Maggie 93XX conversion or even a 93XX scratch build I might as well do it right the first time.

About to pull the trigger to get this thing started. What's the best Edcor PT to use?

I'm thinking...

PT: XPWR155
OT (x2): CXSE25-8-5K
Choke: CXC125-10H-200ma

Also... 2 separate smaller chokes after the main power supply, yes? (5H / 250R).

Thanks
 
Those are the part number I used in mine (except for the XPWR155...but the 155 is fine).
Also, YES on the 5H chokes.

Go for it. This is an extremely nice amp.
 
Thanks for the reply!

Couple more questions....

Is a Hammond 17x10x3 chassis big enough? Yours looks pretty tight and you posted it was 17x11x3. Not sure if that inch will be a problem or not... Any other good chassis sources?

Also, any chance you have a pic of the inside of yours?
 
17x10x3 is perfect. It is the standard dimensions of the KT88 kit that was offered by a member of DIYAudio (and maybe AK too) for a while. Not the least bit cramped.
 
Sweet.

Transformers ordered. ;)

Working up a parts order and starting on the layout. Couple more questions...

I'm rotating the transfomers and choke 90 degrees. I want to rotate tube sockets too for best appearance. I can't tell from the pic of yours which way yours are oriented. Where should the locate notch point for best effect?

The 2 caps mounted on top.... Are they electros for the power supply? I plan on using decent electros instead of film. Reading in the other thread that seems to work fine - especially if decoupling the driver stage with with a choke (times 2) and another electro. Is this a bad idea?

Again - any other pics (guts, rear view, etc.) of your build would be greatly appreciated.
 
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