Decware SE84 clone

jdsalinger

AK Subscriber
Subscriber
Last weekend I finished my SE84 clone and now have over 20 hrs on it, so thought I'd write a report.

This project started out with me being really excited about the clear and open sound I got from my Pilot 402 and wanting to to try to scratch build a power amp using Pilot transformers. I found a trashed Pilot 602 locally and bought it for parts. I didn't have a SE tube amp at the time, so after giving it some thought I decided to build an SE amp instead of a second PP. So I parted out the amp and sold the PP OPT. Tried to sell the PT, but it didn't go. So, I started to look into what I might be able to build with it.

The PT is just a massive hunk of iron. It was designed to use SS rectification (no 5V tap) but the Pilot 602 schematic showed that it could produce 330VDC rectified. So, I started looking for SE schematics with lower B+ SS rectified voltage. Not many out there, I can assure you. I came up with a few from DIYAudioProjects.com including a 6V6 and a 6CY7, but then I discovered the Decware Zkit schematic and realized that it used SS rectification and a B+ of about 325-350V. I had been very interested in Decware SE84 from all the reviews from happy customers. I decided that THIS was the amp I wanted to build.

Total cost, not including tubes was $200. Mouser, Parts Express, Edcor. See the Decware Zkit BOM for part numbers. Thanks Steve Deckert!! You da man!

I used a Hammond aluminum chassis 15x7x3. Just a bit larger than the Decware chassis with plenty of room to spare.

I really like the Decware layout and was torn at how to lay mine out, but in the end, I decided like the asymmetrical look of the PS on one side and amp on the other side. Plus, I liked the clean look of hiding the input jacks and speaker binding posts in the back to hide wires.

I left room for a future tube diode if I wanted, but I've never had an SS rectified tube amp before and from reading about them, they kind of seem like they offer more advantages in terms of punch.

I used Edcor CXSE 25watt OPT on a previous SE amp. They were impressive, but very expensive and I think overkill. I wanted to see what the GXSE could do and trusted it because that is what Decware specifies in their Zkit. The Pilot 402 and DGSE1 amps both have small OPT yet still produce very full bass. I'm sure others will disagree, but I no longer feel it necessary to use giant iron...especially for my type of listening. I have NO regrets for using the GXSE. More on that in the review section.

I had to replace the 6watt 1K power resistor with a 50watt one because when I first fired up the amp, the 6 watt resistor started smoking. ????

Regrets or things I would do differently
1) I think a shorter chassis would be OK. 3" is quite tall and the metal is kind of thin. More of a tactile thing. It doesn't sag at all.
2) Smaller coupling caps. I had great luck with the Audyn 1200V cap on a previous preamp build. They sound great but they're huge.
3) NO stranded wire. I hate that stuff, but I was too cheap and lazy to go pick up some and ran my heater wires with stranded. Not a huge deal, but I just hate that it doesn't stay put and it makes for ugly soldering.
4) Belton Micalex tube sockets vs. ceramic. A lot of amp kits use ceramic, so I thought I'd give them a try. Normally I use Belton as my standard. Boy, what a mistake. These ceramic sockets suck. Grip well, but springy and hard to insert. And the gold retaining rings look very cheap and flimsy.
5) I honestly think I would buy the Zkit board and UFO OPT from Decware next time. It would save so much time to not have to build a chassis and do PtoP wiring. Heck, even integrating the board into the chassis wouldn't look half bad. I just don't like the idea of board mounted sockets.
 
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Pics
(see what I mean about the ceramic sockets?) Actually, that LH tube can be adjusted to straight up.

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The sound is absolutely everything I hoped for. I had been really wanting a DHT like a 2A3 or 300B, but the cost is just way more than I wanted to shell out right now and I've learned that great sound doesn't necessarily have to cost a king's ransom. And after reading Steve Deckert commenting on customers selling their DHT after purchasing a Zen SE84, I figured it would be a great cost to performance amp if not better than a DHT. Not trying to start a war, just saying that I appreciate value.

I love clean and clear highs and this amp has that in spades. There is more detail and separation (both channel separation and instrument separation) I feel than any other amplifier I've heard. On live jazz recordings, I can eavesdrop on conversations in the audience. I think I hear inhaling of musicians on studio tracks like Donald Fagan's "Morph the Cat". Vocals seem to float in the middle of the room with instruments off to the side.

I had not given the EL84 much credit in the past. I just figured it was a ubiquitous "work horse" tube. Well, after really loving the sound of my 2 Magnavox 9302's, RCA RS177 and the Pilot 402. It finally dawned on me that the EL84/6BQ5 is simply a wonderful sounding tube that my ears really like. It was the Pilot amp that really opened my eyes. Pipsqueak output transformers and it still sounds so open full and airy. It turns my head every time I listen to it. Now after hearing it in SE, I am even more amazed at what it can do. I'm excited that such a reasonably priced and available tube can sound so good.

This amp is transparent and makes you want to listen to all your tracks again, for the first time. It is emotional. Tracks like " Just a Song Before I Go" has that warm, but detailed feeling like you're in a carpeted room with CSN. Modern Jazz Quartet "Pyramid" bursts with openness. Sound stage seems 20 ft wide and you really get a sense of the room the recording was made in. The guitars at the start of "Any Major Dude" are bright and metallic. Like I said, I hear new details that I've never heard before on other tracks.

Main speakers for this amp would be my Three Pi 2-way horns (95dB). They are a special and unique speaker. Very dry. But they they LOVE flea watt tube amps. That dry sound becomes organic, extremely detailed and life-like after my ears get accustomed to them. These speakers were designed and intended on being used with sub woofers. But this amp really brings out the best in them, out of any amp I've tried with them. I can actually listen to some pop tunes and don't feel the need to use a sub. There are some deep bass notes that don't shake your pant legs, but you just sense the low freq are there.

This amp is not powerful. I have no volume pot and my computer volume is about 75% with Spotify volume pegged. But hey, I don't need it any louder than that.

I purchased all the recommended tubes to see which are best. I have Svetlana SV83 and TAD EL84 STR. I think so far, I much prefer the TAD. Very full and more of a high quality sound. I realized after I purchased the SV83 that there are supposedly some counterfeit tubes that Decware does not recommend for some reason.

Driver tubes are a Russian 6N2P, NOS Sylvania 6DJ8 and NOS Sylvania 6922. Can't say that I notice a difference in any of these yet, but the amp is still breaking in and I'm still getting used to it. Have to get familiar with my favorite tracks before I can compare driver tubes.

Anyway, I'm really digging this thing and highly recommend it to anyone on the fence.
 
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This amp is NOT powerful. I have no volume pot and my computer volume is about 75% with Spotify volume pegged. But hey, I don't need it any louder than that.

You list a Forewatt in your signature, but don't mention it here.
I used to own a couple SE84Bs and found they worked better for me with a preamp.

Nice build and glad you are enjoying the amp.
 
I use the Forewatt, and it DOES make EVERYTHING sound better. But I have some issues with using it with the SE84. Here's what happens; sometimes I plug the preamp into the amp and....nothing.
Then I unplug the interconnect at the amp...hum/pop and then it works. When I first used the Forewatt in passive mode, it worked fine with the SE84.

Input jacks are grounded.

No problem going directly from the DAC into the SE84. And Forewatt into another power amp is fine too. They just don't play well together.

What would cause that? Is something not grounded?

On the SE84, I do not currently have the incoming power module grounded. I kind of thought that was optional and sometimes advised against for ground loop reasons.
I also realize that it is good to ground the power module for safety reasons. But I've used the Forewatt on other vintage power amps with 2 prong power cords and never an issue.

Edit: There is an issue with the Forewatt. Strange coincidence. It worked for a while. Must have been a fluke that it worked on my M2 after it cut out while using it on the SE84. Now I get nothing on any amp in active or passive modes.
 
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Regrets or things I would do differently
1) I think a shorter chassis would be OK. 3" is quite tall and the metal is kind of thin. More of a tactile thing. It doesn't sag at all.
2) Smaller coupling caps. I had great luck with the Audyn 1200V cap on a previous preamp build. They sound great but they're huge.
3) NO stranded wire. I hate that stuff, but I was too cheap and lazy to go pick up some and ran my heater wires with stranded. Not a huge deal, but I just hate that it doesn't stay put and it makes for ugly soldering.
4) Belton Micalex tube sockets vs. ceramic. A lot of amp kits use ceramic, so I thought I'd give them a try. Normally I use Belton as my standard. Boy, what a mistake. These ceramic sockets suck. Grip well, but springy and hard to insert. And the gold retaining rings look very cheap and flimsy.
5) I honestly think I would buy the Zkit board and UFO OPT from Decware next time. It would save so much time to not have to build a chassis and do PtoP wiring. Heck, even integrating the board into the chassis wouldn't look half bad. I just don't like the idea of board mounted sockets.

This is great feedback for any DIY tube project.
 
I appreciate that, Sound.

I hope this report encourages others and helps them avoid my mistakes. That's the only reason I wrote it.
If not for AK & DIYAudio build threads, I don't know that I would have discovered the joy of building my own gear.
 
I appreciate that, Sound.

I hope this report encourages others and helps them avoid my mistakes. That's the only reason I wrote it.
If not for AK & DIYAudio build threads, I don't know that I would have discovered the joy of building my own gear.

Reading insights on what to change after a project is completed is as valuable as knowing what went right.

Great feedback on the sockets specifically, I've wondered about those too.
 
That large aluminum finned resistor won't run hot enough to melt the plastic zip tie will it ?
 
I considered that but haven't checked yet. Zip tie is rated 185 deg F or around that.
I have a laser thermometer at work, I'll bring home and check.
 
Nice build!
At first glance it looks like a scratch build DGSE amp (no bad thing)
Probably similar
 
Nice build!
At first glance it looks like a scratch build DGSE amp (no bad thing)
Probably similar

Thanks. The last amp I built was a DGSE-1. It sounded clear smooth and detailed, but had more of a PP sound than SE.
I really need to let the enthusiasm of novelty of this current amp settle down before I write much more about it.

Schematically, there are quite a few differences. The Zkit doesn't use NFB, is SS rectified and uses CRCRC filter. DGSE uses NFB, tube rectified with CLCRC and operates at about 100V lower B+
Several other differences in the schematic. I'm not a designer, just a DIY'er, so I can't comment on the significance of the differences.

I put a laser thermometer on the 50w power resistor and read 130 F after an hour of use. The zip tie was only around 110-114 F.
I think I'll let it be, since the reason for zip tying is to eliminate screw heads in the side of the chassis.
The zip ties are rated to 185 F. I think that's the point where the strength rating of 75lb drops off, not where it melts. Not only that...I'm sure there is probably 20-30% safety factor in there.

Forewatt is still acting weird. Last night I was able to use it on the SE84 in active mode. This morning, I fired it up and nothing. No sound.
I was thinking last night that it was a Spotify bug. I had some quirky issues with my computer and Spotify on another amp. Seems like when you unplug interconnects, sometimes Spotify will pause and you have to restart it.
 
I'm not a designer either .
I'm somewhat at a loss to hear your more push pull description. I'm not even sure what that means, but obviously SE is SE.
I know the voltages on the DGSE were optimized for the plate curves,( most linear region of the el84.
My thoughts are the iron would be the biggest difference in the 2 designs .Perhaps different impedance requires different tube voltages.
And lack of feedback

Designing around the iron called for the feedback .
Those OPTs may not require the feedback.
As they say , there is no free lunch. There are drawbacks and compromises
Ultimately it comes down to your enjoyment .
The DSEG was made (tweaked?) To still be a magnavox. Most who have made one feel it was a smash hit.
Not being locked into any pre conceived design parameters, let's the Decware do pretty much anything. I suspect it has a degree of refinement the maggy is lacking.
Itd be interesting to see some test data.
Even at that , it doesn't tell the whole story.
Sorry about the side track.
I think it'd be interesting to hear your impressions of the 2 when you get a chance. Enjoy!
 
Here are the voltages I'm measuring.

Rectified voltage between bridge rectifier and first resistor: 378V
Ua = 300V. Decware schematic shows 346 +/- 10V at point A.
Ug1 = 10.5V Decware schematic shows 10.25 +/- 2V Data sheets show -7.8V

So, I looked at the el84 tube data sheets and plate characteristics. Seems that Decware is calling for running Ua 46 volts higher than max (300V)
Also, appears that generally, Ua is recommended to be should be around 250V. In that case, the DGSE-1 is much closer to optimal (255 V).

Another thing I noticed is, according to the data sheet, the nominal Ug1 is -7.8V. I'm running -10.5 (Decware Zkit calls for -10.25 +/- 2V)

I was going to drop the value of the first resistor (1K) to around 400-450 to try to get my voltage at 'A' closer to Decware's recommendation.
But looking at the el84 plate characteristics, the graph doesn't even go past 300V Ua and the curve for the -10V bias is very flat.
Not sure I want to, or if it would be noticable to increase my B+ to match Decware. I'm thinking I'll just leave it as is.

https://drtube.com/datasheets/el84-jj2003.pdf
 
Great stuff. I was actually looking into building one of these. I would probably use their board and build my own wood chassis with a metal top plate. You mentioned in your first post you would probably go with a Decware UFO OPT - do they offer that option? I had pondered the same thing, but I didn't see where they had those for sale.
 
You should email Steve. He may sell you a pair, even though they don't offer them on the site. I think I saw a post on the Decware forum where someone was able to purchase a pair.
I know they offer upgrades for Zen owners who bought before they came out with the UFO XFMR.

Good call on using their PCB. It should save you a lot of time.
 
Bought the PC board and added a note asking if it was possible to buy the UFO transformers. I'll let you know what they come back with.
 
Last weekend I finished my SE84 clone and now have over 20 hrs on it, so thought I'd write a report.

This project started out with me being really excited about the clear and open sound I got from my Pilot 402 and wanting to to try to scratch build a power amp using Pilot transformers. I found a trashed Pilot 602 locally and bought it for parts. I didn't have a SE tube amp at the time, so after giving it some thought I decided to build an SE amp instead of a second PP. So I parted out the amp and sold the PP OPT. Tried to sell the PT, but it didn't go. So, I started to look into what I might be able to build with it.

The PT is just a massive hunk of iron. It was designed to use SS rectification (no 5V tap) but the Pilot 602 schematic showed that it could produce 330VDC rectified. So, I started looking for SE schematics with lower B+ SS rectified voltage. Not many out there, I can assure you. I came up with a few from DIYAudioProjects.com including a 6V6 and a 6CY7, but then I discovered the Decware Zkit schematic and realized that it used SS rectification and a B+ of about 325-350V. I had been very interested in Decware SE84 from all the reviews from happy customers. I decided that THIS was the amp I wanted to build.

Total cost, not including tubes was $200. Mouser, Parts Express, Edcor. See the Decware Zkit BOM for part numbers. Thanks Steve Deckert!! You da man!

I used a Hammond aluminum chassis 15x7x3. Just a bit larger than the Decware chassis with plenty of room to spare.

I really like the Decware layout and was torn at how to lay mine out, but in the end, I decided like the asymmetrical look of the PS on one side and amp on the other side. Plus, I liked the clean look of hiding the input jacks and speaker binding posts in the back to hide wires.

I left room for a future tube diode if I wanted, but I've never had an SS rectified tube amp before and from reading about them, they kind of seem like they offer more advantages in terms of punch.

I used Edcor CXSE 25watt OPT on a previous SE amp. They were impressive, but very expensive and I think overkill. I wanted to see what the GXSE could do and trusted it because that is what Decware specifies in their Zkit. The Pilot 402 and DGSE1 amps both have small OPT yet still produce very full bass. I'm sure others will disagree, but I no longer feel it necessary to use giant iron...especially for my type of listening. I have NO regrets for using the GXSE. More on that in the review section.

I had to replace the 6watt 1K power resistor with a 50watt one because when I first fired up the amp, the 6 watt resistor started smoking. ????

Regrets or things I would do differently
1) I think a shorter chassis would be OK. 3" is quite tall and the metal is kind of thin. More of a tactile thing. It doesn't sag at all.
2) Smaller coupling caps. I had great luck with the Audyn 1200V cap on a previous preamp build. They sound great but they're huge.
3) NO stranded wire. I hate that stuff, but I was too cheap and lazy to go pick up some and ran my heater wires with stranded. Not a huge deal, but I just hate that it doesn't stay put and it makes for ugly soldering.
4) Belton Micalex tube sockets vs. ceramic. A lot of amp kits use ceramic, so I thought I'd give them a try. Normally I use Belton as my standard. Boy, what a mistake. These ceramic sockets suck. Grip well, but springy and hard to insert. And the gold retaining rings look very cheap and flimsy.
5) I honestly think I would buy the Zkit board and UFO OPT from Decware next time. It would save so much time to not have to build a chassis and do PtoP wiring. Heck, even integrating the board into the chassis wouldn't look half bad. I just don't like the idea of board mounted sockets.

I'm inspired to do a DIY tube build which would be my first. With that in mind Regret #5 resonates with me.
Thank you for the detailed breakdown.
 
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