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planning DIY SE KT88 build

invaderzim

invaderzim

Super Member
I'm gathering parts for my first build:
http://diyaudioprojects.com/Tubes/KT88/

It lists a 5H 250R choke and I haven't been able to locate one.

would this work?
Inductor; Filter; Ind 6H; Tol -20%; +50%; Cur 200mA; Leads; DCR 150 Ohms

amp01.jpg
 
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There are at least several threads on this amp on AK and DIYAudio.com. The schematic you posted is very simple and would probably sound great.
But I would recommend reading this thread http://www.diyaudio.com/forums/tube...8-build-abdellah-diyaudioprojects-design.html

I built that amp (well...a refined version) and read as much as I could to understand what works and doesn't work. don't bother experimenting with all the tweaks you read. Just build the basic and be happy.
I rolled EL34 power tubes and 6GU7 preamp tubes. There isn't any noticable difference. LED cathode bias isn't worth trying either. I couldn't tell any difference.

Oh, btw, I used a 10H choke from Edcor. CXC125-10H-200mA
 
Lavane said:
Here is one. 150ma enough? http://www.angela.com/hammondchoke194d.aspx
Click to expand...

That's what I'm not sure about. In the power circuit it has a 10H 200mA but I wasn't sure about the specs on this one with it being 250R and not listing a mA rating.

jdsalinger said:
Oh, btw, I used a 10H choke from Edcor. CXC125-10H-200mA
Click to expand...

That's what I was planning to get for the one shown in the power circuit but it shows a second one on the amp circuit. Is that a mistake in the schematic or does it really need two so close together? Or am I reading the 5H 250R wrong?

choke.jpg


There were a couple of references in the other thread about the 5H choke but there weren't any answers about it and the schematics mentioned wouldn't show up anymore
 
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jdsalinger said:
But I would recommend reading this thread http://www.diyaudio.com/forums/tube...8-build-abdellah-diyaudioprojects-design.html

I built that amp (well...a refined version) and read as much as I could to understand what works and doesn't work. don't bother experimenting with all the tweaks you read. Just build the basic and be happy.
Click to expand...

Thank you for the tips and the thread link. I've read through a few on the amp, but often they quickly get more technical than I can currently grasp. I get the basic operation of the components but the math tends to lose me. But it is fun actually learning as I go.
 
Oops. Sorry for the confusion. The second inductor is correct. You need both the 10H in the power supply and the 5H on B+
I and most builders use (2) 5H inductors. One for each channel.
 
that makes sense, probably not the best idea to try to save $20 by tapping into the B+ power after those rather than splitting before. I'm about half way through the recommended thread and it looks like the:
Hammond 155H, 5 Henries, 50mA, 270 ohms, 400VDC
is one that people have used for that spot. Is the 50mA sufficient? It looks like 2 of those should pretty easily fit inside the case rather than distracting from the pretty edcore transformers on top :)
 
That's what I used. 155H I would post a pic, but I haven't figured out how to do it yet. Much easier on the old board.
I think the actual amp draw is more than 100mA total but that is the only choke I've ever seen used on this amp.
 
question on the output transformers

I was looking at getting the Edcor GXSE15-8-5K based on a recommendation in this thread: http://www.diytube.com/phpBB2/viewtopic.php?t=5347
But then it was pointed out to me that "The GXSE transformer is OK but being a guitar one, has a cut off on the bass end of around 30-40HZ. The CXSE ones are good down below 20HZ and would be my choice."

Am I sacrificing a lot of sound quality for the money savings?
Would it be that much better to get the: https://www.edcorusa.com/cxse25-8-5k?
or should I melt the credit card and do the original ones spec'd: http://tctubes.com/james-transformers-JS-6123HS.aspx
 
The only down side to Edcor is their extremely long lead times (6-8 weeks I think). But it's an American made product (not sure if you are in the states, or outside).

If this is an experimental project for fun and you build a lot of amps, you could go with the 15-8-5K and I bet it would sound fine, especially if you plan to use a powered sub.
Reviews for the 15-8-5K are favorable.

However, if you want to built a premium, once-in-a-lifetime amp and have it look muscular and never wonder "what if".... the 25-8-5K is the one you want. I was shocked at their size when I pulled them out of the box. They are so incredibly FAT and balance out the size of the power tranny. It's only about $100 more to upgrade from the 15-8 ( a trip to the grocery store? ).
Plus, it sounds like you have the budget for James, so stepping up to the larger Edcor should be a reasonable trade-off between the two extremes.
I chose the larger CXSE25-8-5K and didn't regret it.

I can't imagine HOW on earth the James OPT are worth three times the cost of the Edcor. I have never considered James and never wondered "what if" about those.
This amp is expensive enough as it is. Here is mine.
IMG_9613.JPG

Two things that I would change about my layout.... I would definitely turn all tubes 90 degrees because the best glow is facing to the sides the way I did it (I was thinking about the socket fasteners and after it was complete and warmed up, "DOH!").

Also, I wonder if turning the OPT and power transformers and the choke 90 degrees would have looked better. So you are looking at the bell end cap and can read the Edcor name (on the OPT & choke). Very minor, but you may want to lay yours out to see what you prefer.
 
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excellent advice on the OPT. The plan originally was to do an inexpensive, small build as a starter project but that quickly escalated. All this from dragging a nearly 60 year old Heathkit A-9C out of the attic and connecting some old speakers I'd never bother to throw away. Next thing I know I'm sending the half price Marantz amp back to Crutchfield and obsessively looking up tube amp info.

That is a great tip, I would never have thought about orienting the tubes for maximum glow effect either.

That looks sharp, what are the dimensions on the chassis?
 
I've also built this amp, I didn't use the 5H choke, or the 10uF poly cap for the power supply decoupling. Is there any benefit to adding this? The amp is dead quiet as-is.
I also used the Hammond 1628SE OPT's, and am happy with the sound, bass is very good for an SE amp. They are very substantial OPT's at 11lbs each!
I also changed my power tube bias to LED's, and thought it made an improvement in the sound to my ears.
Add a three-way switch so you can try Pentode mode as well as UL and Triode. I find Pentode with EL34's is very good sounding for rock. More distortion, but a little more power also. Not really noticeable unless you turn it to "11" :)

This amp was a very good sounding design, and going to it from a PP topology was surprisingly better sounding than I thought it was going to be.

Good luck
Glenn
 
11x17x3 were the dimensions that I used for the chassis (I think). I'll measure tonight and if different, I'll edit this post.
 
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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hmm, I just read one comment where someone suggested using a wine crate for a chassis and I just found one in about the right dimensions.
 
Not much help here but following along as I'm considering one of these.

For the chassis, steel can be a bear to cut/drill but the Hammond aluminum ones I've seen are really thin. Not sure they would hold up to the heavy transformers...
 
The steel ones are a pretty soft metal. I didn't have any problems using a step drill to punch socket holes. Just don't get a stainless steel chassis. They are way too hard. I had several bits weld to a SS chassis trying to drill a few holes.
 
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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