New Build

a 3W single ended EL84 amp for home, work & school

Re: New Build

Postby MacL » Tue Jan 14, 2014 3:47 pm

I understand you wanting a show piece and I applaud you building yourself. Someone will use your pieces in the future and I try to help out them out by including the schematic and transformer specs on the inside bottom of the my project chassis. I have built a few guitar amp chassis from scratch and I have learned a couple tricks but I sure there are others more advanced than I that could advise.

Drill bits for tube holes - if you don't have a punch. I used to use step bits - but now purchase a cheap new 3/4" spade (wood) bit (disposable) to use for 12ax7's and el84-people will laugh - but I dare anyone to try and compare the quality of the first half dozen cuts.

Use a IEC socket with integral fuse.

Buy a hand nibbler to cut socket hole in aluminum if you don't have a punch-drill large hole first and nibble the rest out.

Use stainless steel bolts, washers, and lock nuts and good Belton tube sockets.

I worked a few turret board board builds but I am really coming around to quality PCB pieces like Shannon sells- the screw terminal blocks are great and I may even be swayed to prefer board mounted sockets someday.

GOOD LUCK
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Re: New Build

Postby AmadeusMozart » Tue Jan 14, 2014 10:57 pm

Yeah, woodworking tools work fine on aluminium as long as you do not go too fast. I have actually ordered a tungsten tipped hole saw that's integrated with the centre drill bit (unlike the hole saws that are more or less sitting loose on a spindle).

I always use SS fasteners, nothing worse than rust etc. (actually on audiokarma.org are pictures of my 6L6-GC SE build, same name, about three years ago). And yes I always include the schematics, nothing worse than have to guess what parts and voltages are when you need to do a repair on someone else's work.

If you get an ordinary HSS spiral router bit, preferably 1/4" then you can happily use it in a router, once again go slowly and cut only a few mm at a time. Use beeswax as lubricant. Wear proper clothing, safety glasses and hearing protection - slivers fly everywhere so not a job to do in the lounge (wink).

I've used J B Weld to glue everything together and then afterwards drilled for 3mm countersink screws and used that to fasten afterwards. Then fill the countersink side up before putting the undercoat on.

Before ordering from the US (cost of freight is more than the cost of the actual item) I'm going to have one final attempt at getting something made in our country. Prefer to have some jarrah at the ends.

16 January - Had to bring some relatives to the big city (201 Km away) to catch a flight back overseas. After dropping them off I visited a sheet metal outlet and they managed to bend some 1/8" aluminium in a U-shape with some lips on the bottom. Had to come back two hours later to pick it up that was fine with me - did some shopping with the wife in a mall close by. It still needs a bottom plate and some wooden sides but at least it is the size I wanted and it is very sturdy. Needs painting but I am pleased, now I can move forwards without having to wait.

20 January - Got notification that the Hammond Power transformer has been shipped. Don't know what the break points (in weight and size) for charging shipping are but these were shipped without shipping costs so for the price of Edcors + freight I now have Hammond and a beefy one to boot. Chassis is slightly oversized for the budgy but that allows me to change to a different SE if I need to (hopefully not, have yet to hear a bad 6BQ5)

28 January - most holes have been cut and am waiting on a parcel with the RCA and speaker connectors from tubesandmore. Once that arrives I can drill those holes and clean the aluminium and paint. Only machine screws visible on the top will be those for the transformers and choke. Layout has been a pain because the power transformer is universal and has many voltages so had to find a place to leave those surplus wires. (plus it has a CT 5V for rectifier, three more wires to leave somewhere safely)
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Panic and later relief

Postby AmadeusMozart » Tue Mar 04, 2014 10:16 pm

After a stroke and partial loss of right hand movements the amplifier has been finally finished by my wife. Soldering has not been up to my usual standard but am not complaining.

Am using DSSF3E software as tone generator and it goes from 10 Hz to 20 kHz. Bought on the local auction website an old scope and hooked it up. Panic: at 100Hz nice square wave but at higher frequencies irregularities. Volume change - still same shape. Disconnected feedback - still present. Take out output tubes - still present on anodes of ECC803S. Powering down - same shape and nicely gradually whole shape reducing in size, surely cannot be parasitic oscillation?Hmmm.... Tried some bypass capacitors - no change, still present.

Hook up solid state amplifier - same irregularity, ok, no problem: scope needs recapping / re-alignment. Relief.

Ruler flat response from ~ 18 Hz to 16 000 Hz (as designed), minimal rise at 10 Hz and slight drop off at 20 KHz.

Some changes to the design were made: B+ lowered to 265V (250 V at plate), cathode resistors 140 Ohm each. A 100 Ohm resistor between UL tap and g2. A 1000 pF capacitor between plate and g2. (both recommended by Langford-Smith of Radio Designer Handbook fame), V1, V2 & V3 g1 input resistors increased to 10k. A 100 pF capacitor across the resistor to ground of V2 and V3. Input resistors V2 & V3 increased to 340K.

Overal pleased with the end-result.
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Re: New Build

Postby Shannon Parks » Wed Mar 05, 2014 9:36 am

Looks beautiful on your desk. Thanks for the thread updates and documenting your mods. I hope to revise the Budgie SE project this summer and everyone's feedback has been helpful.

Best of luck in your recovery - it certainly sounds like you have a heckuva wife!

Shannon
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Re: New Build

Postby AmadeusMozart » Fri Mar 07, 2014 11:51 pm

I do not remember if I documented that I made a slight change to the power supply - I used a large Hammond transformer and in order to limit the peak current I used immediately behind the rectifiers a 300 Ohm adjustable resistor followed by a 30 uF /350 WV AC motor run capacitor. The transformer I have is the "universal" one and it has multiple taps for the mains voltage. I tried to adjust the filament voltage to exactly 6.3V in by selecting another tap. That did not work - could not get it low enough. Using a resistor in series with the mains to adjust the filament voltage to obtain exactly 6.3V AC was the solution (was often done with tube testers, they had an adjustable rheostat).

I still have one more job to do - I have an aluminium bottom plate but when I put it on I can hear a slight hum. Need to find a way to dampen it.
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Re: New Build

Postby AmadeusMozart » Mon Mar 17, 2014 11:13 pm

Slight transformer hum, with bottom plate more noticeable.

Put a bit of stiff foam between the bottom plate and the top of the choke, slightly (approx. 1 mm) bending the bottom plate. No hum at all, perfect. Perhaps the mains transformer and the choke were slightly interacting with each other.

Have a resistor in series with the mains and measuring the current across it I've calculated that I am using 62 watts. (running the tubes at 250V / 50mA on the plate).

Been using my Mac mini which is running windows 8 with a 31 band equalizer to smooth out the room curve. Speakers are the FF105WK metronome (88 dB) but I am not lacking anything in bass region or SPL levels. Very satisfied, thanks Shannon.
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Re: New Build

Postby Shannon Parks » Tue Mar 18, 2014 12:49 pm

AmadeusMozart wrote:Put a bit of stiff foam between the bottom plate and the top of the choke, slightly (approx. 1 mm) bending the bottom plate. No hum at all, perfect. Perhaps the mains transformer and the choke were slightly interacting with each other.


Maybe the foam is damping a 120Hz vibration?

AmadeusMozart wrote:Been using my Mac mini which is running windows 8 with a 31 band equalizer to smooth out the room curve. Speakers re the FF105WK metronome (88 dB) but I am not lacking anything in bass region or SPL levels. Very satisfied, thanks Shannon.


Great to hear this, and thank you.

Shannon
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Re: New Build

Postby AmadeusMozart » Tue May 30, 2017 8:09 pm

It is some time since I have posted an update. This amplifier has been running 5 days/week and 8 ~ 10 hours/day. It has proven to be the one I liked the most of all that I've owned previously which had SE 6L6GC, 4 x KT88 PP monoblocks, EL34 PP, Leak 20, Quad II amongst the more well known ones.

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inside view
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Re: New Build

Postby AmadeusMozart » Wed May 31, 2017 10:01 pm

I'm looking for a second SE Budgie amp board for building another one for one of my children. If one does not turn up then I'll be doing point to point wiring like I did when i build my 6L6GC amplifier (a heavy beast with James transformers and choke but not as satisfying as the little Budgy). Chassis was made with some sheet and angle aluminum, screwed together with JB Weld metal expoxy. Some pic's of the 6L6GC build attached.
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