Weekend Project - JE Labs EL-34 SE Amp

[TomMcNally]

I got the bug to build this Friday night and finished it up Saturday. This is a JE Labs EL-34 Single Ended stereo amp. It uses a Hammond 272HX power transformer, 193G choke, Edcor XSE15-8-5K outputs. I used a pair of new Tung-Sol 6SL7's, and a pair of Tesla "Firecracker" EL-34's I had left from the original eight that came with my Velleman K-4000. Unfortunately, one of those true to their legend blew the fuse as soon as the JJ "New Firecracker" GZ-34 started to warm up, so I popped another one in and it worked fine. The 6SL7 sections are paralleled in Joe Esmilla's design.

This is single ended amp with some kick ! It was an easy build and sounds great. It looks nice in the dark, since all of the tubes have a nice visible glow. The schematic is available on Angela Instruments site http://www.angela.com/catalog/how-to/SE.EL34.html. The amp runs fairly cool, with only a little hot spot above each 880 ohm/25 watt cathode resistor. I used ReliableCap's AudioCap polyprop/aluminum coupling capacitors from Handmade Electronics.



Upon investigation, the brown substance on the edge of the chassis seems to be squirrel poop from the railing on the deck. Yuck.

[SDS-PAGE]

How does the sound of this compare to that of DHT amps? I always wondered how EL-34 sounds in SE mode. So, you're running this in triode mode? You take nice pictures of your amps! Sounds like a fun little project. -Min

[wiredbecker]

Squirrel poop aside, bad ass as always Tom.

[TomMcNally]

Thanks Chris !

Min - I think the sound this amp beats the heck out of my 300B, but since you mentioned the new design, I may rip into that one and see if it improves. I was going to go with the design with the 6NP1, but I didn't have any until last night, when Sal visited me at work and brought me two, wrapped nicely in Russian newspaper.

... tom

[Sal Brisindi]

Tom,
If I were you, I would check those tubes with your Geiger counter, you never know..... Yellow_Light_Colorz_PDT_09

Nice job on your amp as usual.

Sal

[EWBrown]

I've found from experience that EL34s and EL84s sound great in SET mode. Nice amp, looks good as always! Even the nearby squirrel doodie doesn't detract from it Yellow_Light_Colorz_PDT_04

(FWIW your deck rails and mine are nearly identical in every way) Yellow_Light_Colorz_PDT_06

My two EL34 pseudo-SETs are based on the Claudio Bonavolta "EL34SE #3", and the diagram is posted elsewhere in this forum. I ran the cathode current a tad higher, around 50 mA per tube (as opposed to his suggested 64 mA), and the B+ is around the same as yours, around my "typical" 365 to 3780VDC.but as always YMMV, etc.... I started out with Svet EL34s later stuck in some UOS (used old stock) Amperex EL34s (pulled from a "dubious" ST70 that I obtained a LONG time ago) and UOS Tele 12AX7s, and it "kicks butt" Yellow_Light_Colorz_PDT_03 other than a tad o' ripple / hum, as I wasn't all that savvy on the subtleties of single point grounding at the time. Not bad enough to re-wire, so I've left them be.


/ed B in NH / NC

[TomMcNally]

I realize I didn't answer your question Min - yes - the EL-34's are in Triode Mode - 100 ohm resistor from plate to screen. I could try ultralinear since the Edcor OPTs have a tap ... by the way ... they are 5K but I see that most of the other designs are using 2.5K ...

I did look at Bonavoltas design ... I wanted to use octals so I went with the 6SL7's that Joe Esmilla came up with Ed. Yeah my deck needs a good power washing and maybe I'll get around to staining it someday ... it's got that seashore weathered look.

I'll measure some voltages today, nothing is running hot, I touched all the resistors yeaterday when I turned it off and took the pictures.

... tom

[jduffy]

Great amp per usual. I love the industrial look your equipment has. It looks like it belongs in a radio station back in the 50s.

And I don't think that's poop on the deck (no pun) but some kind of moss or mold or something. I remember getting that stuff on wood when I lived back east. You must have been getting some serious rain for that stuff to appear.

[EWBrown]

The 6SL7s are probably a better match for the EL34s, the extra 12AX7 gain isn't needed for 99% of cases.

I found that SET mode was around 5WPC and UL mode was 7.5WPC, using 3K (SET) or 3.5K (UL) OPTs. The 5Ks will deliver a tad less power, but also significantly lower THD, so it is a good trade off, the difference of a watt is hardly audible, anyway, but the THD improvement is.
I've used 5K OPTs with 6B4Gs, too, and the sound is superb!.

I don't have the "sea washed" deck,s being around 60 miles inland, but there is a slight greenish hue of algae on the 6 year old portions of the deck, as the area is woodsy and not a lot of direct sunshine to dry it out.

I gave up on hanging bird feeders after the third late-night visit by a black bear, which totally destroyed my feeders. :o Squirrels and chipmunks are one thing, but big black bears aren't in the same league, and I didn't want them to "test" my glass sliders. :o Yellow_Light_Colorz_PDT_07


/ed B in NH

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Thanks for the info, Tom. It looks like you can use other tubes like KT88s, 6550s, KT66s, etc in lieu of EL-34s with no major modification. How versatile! I am somewhat surprised by the fact that those Edcors have a UL tap. I used them to build 13EM7 amps last time, so I don't remember what taps there were besides 5K.

[EWBrown]

I'm more than certain that the decware 4.2K / 6 ohm SE OPTs I got a few months ago are indeed made by Edcor, other than having wire leads, rather than solder tabs, they look identical... They even have the same blue plastic bobbin and the labelling on top of the frame looks the same Yellow_Light_Colorz_PDT_11 The decwares also have a label on the side stating "Made in USA" and have a little "OK" hand symbol.

I started yet another small amp project last nite, using one of my oddball dumpster chassis, size 13.5 X 8 X 1.5 inches (same as used for the 6S4PSE amp). Drilled out for one of the MPS 285-0-285 and 2X 6.3 CAX / 2.5A power trannies, and one Hammond 158L choke, plus a few "pilot" holes for the tube sox, etc...
I got a late start, so I didn't get a lot done, but then there is no real rush, either...

The final configuration is still a YTBD work in progress, and will most likely result is 6CK4 SET, with the decware/edcor iron and Angela's "mystery tube" 12AZ7N SRPP drivers. I tested the tubes from Angela last night, and they test near identical to NOS 12AT7s, so I'll give them a try, if they aren't up to snuff, then I can plug 'n' play with other 9A based tubes.

The target for the 6CK4s is approx 270VDC P to K voltage, at around 45 mA which then is a near perfect match for the aforementioned small OPTs. The cathode voltage should be 27-28 VDC, so 600-620 ohms works out - I've already "breadboard" tested it, and it's spot-on. Yellow_Light_Colorz_PDT_03

/ed B in NH

[TomMcNally]

Wow ! Some of you may remember that the receptionist at work brought me a big box of "those bulbs like the ones in that thing in your office" ... I just now looked in the box and took a pair of Leslie branded 6550's and popped them in the SE amp and they rock !

Here is the list of what she brought me ... no EBPlinkers !!!!

BOXED ...
2 - 6550
4 - 6L6GC
2 - 5Z3
2 - 5AR4 (Mullard and Amperex)
1 - 0C3
8 - 6BQ5
4 - 7025
4 - 12AX7A
2 - 12AU7A
1 - 12AT7
1 - 6267
1 - 6AV6
and a bunch of loose ones in the bottom
of the old Lafayette Radio Box

"Boxed" doesn't mean new ... the Leslie tubes were in RCA boxes with $ 10.00 penciled on them from a radio store of old ... probably Lafayette.

[Sal Brisindi]

Tom,
Nice score! The tubes definitely came from an audio/guitar guy.

Sal

[TomMcNally]

I popped in a set of ancient Lafayette Radio branded 6L6's tonight ... they sound great ! You're right Min - this is a universal amp.

[kheper]

I'd like to make one of these SE amps with the Transcender 'economy' SE outputs, available on ebay.