My new 2w amp build project - EF86/ECC83/ECC99

eddy999

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As I wait for my cab to be built and faceplate for my organ conversion I thought I'd get on with a new build. I decided to take the EF86 channel from my other build that I thought worked very well and build it into a low cost/low power amp.

I'm basically sticking with the EF86 channel from my other amp up until the output section, where I'm going to use a single ECC99 dual triode push-pull for around 2w. The EF86 feeds an ECC83 for gain, followed by the other triode as a cathode follower to drive the tone stack. Another ECC83 is used for the LTP PI (no presence control this time), then finally the ECC99 cathode biased. Again this amp will have no negative feedback (same as my organ conversion). This one will have a solid state rectifier rather than tube. I was originally planning to use an ECC82/12AU7 for the output section, but was inspired by Echevarria's recent build to use an ECC99 instead - not a tube I've ever tried before.

One of my goals of this project was to keep the cost down to £100/$150, whilst not skimping on the quality of the important components (this is excluding a cab etc). I'm pleased to say that my current total component cost is £99.98 :)

I've drawn up the schematic, simulated in LTSpice and produced a layout. The layout is mostly point-to-point as this is something I've been interested in trying, plus it helps to keep the cost down again as no turret boards/extra wiring to pay for. My initial attempt at producing the layout was a bit of a mess, as everything was pretty much connected exactly to where it needed to be.. It would have been a nightmare to build/debug however. I've added in a single tag strip to anchor components to and to keep the layout much cleaner, with additional wiring between tags where necessary.

Most components this time were bought from Farnell UK - excellent service, free next day delivery.. A number of components had to be bought in 50s however, but they were still dirt cheap and it means I'm pretty well stocked up now :)

Other bits were sourced from Modulus amplification (chassis, valve sockets and some other bits and pieces), and Ampmaker (the little 4w British made output transformers).

Power transformers are by Antek. It was cheaper to import them including shipping etc than it was to buy a UK made transformer.

I also decided to build two of these - one I'll be keeping (the prototype), and #2 will be sold off most likely.

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laxcdn

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Cool project. Will be interesting to see how the tranformers make it sound.
 

bwillard

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It will be fun watching your build. I'm curious to see how it turns out. I think I caught the amp-building bug...
 

eddy999

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front and rear panel chassis holes drilled and mostly populated (except power switch which i'm still waiting for). As my power transformer has windings for both 115v and 230v mains voltage (and supports 50/60hz) I thought I'd build in a voltage selector switch so it'll run either side of the pond.

From the left: power switch, bass, middle, treble, master, gain, bright switch, input.

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eddy999

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Frustratingly slow progress this evening. The only drill I have is cordless and it doesn't want to retain a charge for more than about a minute of drilling.. Lots of stopping and starting led to some holes that weren't quite on the mark, which made it a real pain mounting the valve sockets..

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Cygnus X1

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Are those Belton sockets?
Been using ceramics but those look nice...
 

eddy999

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Soldano style heater bus wiring with artificial CT. The socket on the right is for the EF86, hence the difference in heater wiring compared to the others.

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eddy999

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PT holes drilled and mounted, primaries wired up. The voltage selector wires the two 115v primaries of the PT in series for 230v, or parallel for 115v.

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Echevarria

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Looks very neat and clean just the way i like it. :)

I am uploading a youtube video of my ECC99 amp as i type, it's taking a while but hopefully will be able to post a link soon. It might give you some idea what the tube sounds like.

I find that using 22k primary on the OT even if it seems higher than what calculations suggest gives me a good balance of compression and chime for a single ECC99 in push-pull (i have my B+ at 310V). YMMV.
 

eddy999

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Heater wiring completed. Power supply section wired up, ready to be connected onwards via the HT fuse. I'm using Panasonic electrolytics - they were a great price and seem to be a decent spec.. The only issue is my layout was based on axial caps rather than radial, which led to some last minute re-juggling :) That's the PT all fully wired up now - I just have to cap off the second 6.3v winding and the unused high voltage tap (top left of the bottom pic).

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Lyle Caldwell

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The modern Panasonics and Nichicons cost less, take up less space, and perform better than the Spragues and F&Ts, etc. I have no idea why so many people are doggedly stuck in the past.
 

eddy999

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Yes I remembered you posting about it on another thread when I was shopping around for caps which helped influence my decision. I have Panasonics for filter caps and a couple of Nichicons for cathode bypass caps, great price too.
 

Lyle Caldwell

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I'm on a quest to limit the number of electrolytics I use as they fail over time.

So in my own builds I now use film and tantalum caps for cathode bypass and electrolytics only for high voltage/capacitance filter caps.

But yeah, if you compare a $0.45 Nichicon 25V 22uf cap to a $1.85 Sprague 25V 25uf cap, there's no reason for the Sprague to cost so much more and take up so much more space. The Nichicon/Panasonic caps are much tighter in tolerance, much lower ESR, and much better across a wide band of frequencies.

And if gets worse when you compare a $3 Nichicon 450V 22uf to a $10 Sprague 500V 20uf cap. In fact, you can use two modern 450V 10uf caps in parallel and get better performance, 900V capability, and still cost less and use a little less space than the old huge Sprague.
 

eddy999

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Hmmm... Now I know I mounted the OT around here somewhere - where has it gone???

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Ah there it is hiding under the lip of the chassis :)

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eddy999

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Passed the first smoke test. High voltage after rectification is as expected, as is the heater voltage. All good so far. The indicator lights up as well which helps! It's nice to be working with a solid state rectifier again after the valve one in my organ conversion, no waiting for the voltage to slowly creep up.
 

eddy999

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Progress with the component wiring. There's plenty of clearance between exposed leads and the structure is very rigid so I'm not worried about any shorts occurring. All leads also have good clearance from the heater bus. Again my layout was based on axial caps, however the radials worked out really well in the end.

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Eigen

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Great build! Can't wait for some tone clips referencing your tube choice man!

(Very tidy!)
 

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