First Budgie SE (Single-ended EL84 amp)

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

Postby Shannon Parks » Fri Nov 02, 2012 5:19 am

Cool to see all your mods worked out nicely, Ed. Great job! So what was the trickiest part of the build? Getting the choke nestled in the sweet spot with wires out of the way?

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Postby EWBrown » Fri Nov 02, 2012 5:00 pm

I had to "try-fit" the choke, before deciding on it's permanent mounting location. Mounted on the chassis box, beneath the front OPT, there was a decent "sweet spot" for it. It was a bit of a squeeze, but it worked.

Plan B would have been to mount it (horizontally) on the left hand end of the chassis box.

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Postby jollyrogr » Fri Nov 02, 2012 10:41 pm

Shannon, in this pic it looks like you mounted the choke under the power tranny?

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Postby Shannon Parks » Sun Nov 04, 2012 7:24 am

Correct - it is nestled under the power transformer. On the main thread I have the exact dims for locating the mounting holes:
http://www.diytube.com/phpBB2/viewtopic.php?t=5563

If you keep the fast-ons from the fuse holder pointed away, the cables short & neat and use the stock bolts, it isn't difficult to squeeze it in. I was worried that Ed's Hammond choke might have been a little larger.

One important note on the choke. It is easy to fire up the amp without the choke attached (by accident). The bleeder resistor is downstream of the choke, so the first cap becomes fully charged and takes a long time to drain itself through its own leakage. So you'll want to manually drain it or wait awhile and verify with DMM if you do that. I'll move the bleeder to the first cap in future revisions.

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Postby jollyrogr » Wed Nov 07, 2012 10:25 pm

I just started soldering mine together and I have a question - what are R22 and R23 for? I don't see it on the schematic and I didn't have resistors for that location, so I checked the pics and sure enough - yours are empty too.

Design change?
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Postby Shannon Parks » Thu Nov 08, 2012 6:57 am

R22 & R23 are resistors (two 1Ks) to form a virtual tap to reference ground for the AC heaters. But the Edcor tranny has a center tap, and I further connected it to the cathode bias of the output. So I'll probably leave them there in future revs, but most of the time they will be unused.

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Postby jollyrogr » Thu Nov 08, 2012 9:29 am

ok. Following the trace I figured it had something to do with the heaters. Another question, have you tried rectifying the AC heaters? I guess if the amp is quiet, there's no need.

My pcb is done. It only took me a couple hours to solder it all up. Congrats on designing a slick and professional kit. Now I have to wait for my transformers to show up. It will be a few weeks yet most likely :(

pics: my J3 terminal is a little crooked but it will work
http://www.diytube.com/phpBB2/album_pic.php?pic_id=178
http://www.diytube.com/phpBB2/album_pic.php?pic_id=176

for some reason the don't work on those urls?
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Re: First Budgie SE (Single-ended EL84 amp)

Postby MacL » Tue Mar 26, 2013 9:35 am

Hi All,
Just ordered the PCB but I will install in/on a 12" x 7" x 2" aluminum chassis - and I think I may locate the on switch and volume pot on the front- so I will have a little more space than most.
I have built a few guitar tube amp in the past -none using chokes. I thought I might try a different choke and mount on top. I noted ed brown used a different choke.
It looked like Ed's MOD -Hammond 156R is rated at 1.5H @ 56 ohms. In general-Is it safe to assume that the more inductance the better (filtering)- as long as the resistance says close to the designed 50 ohms of the original c-24x? Can you hear a 1/2 Henry difference? Just thinking about under $20 "Choke" rolling. $)
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Re: First Budgie SE (Single-ended EL84 amp)

Postby Shannon Parks » Tue Mar 26, 2013 11:19 am

MacL wrote: In general-Is it safe to assume that the more inductance the better (filtering)- as long as the resistance says close to the designed 50 ohms of the original c-24x?

Correct.
MacL wrote:Can you hear a 1/2 Henry difference? Just thinking about under $20 "Choke" rolling. $)

In this application, the B+ ripple is already knocked below the audible range with 1H, so probably not unless you use very efficient speakers. I think hum and noise is about 350uV on my stock Budgie SE.

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Re: First Budgie SE (Single-ended EL84 amp)

Postby perkinsman » Fri Jan 23, 2015 1:13 pm

Hi Shannon,

First post here, was referred by others at AK. I'm a student learning the disappearing art & science of tube circuits for audio equipment. Of course no one teaches tube anymore but luckily my old timer instructor was an a tube audio guy in his younger days and has encouraged me to build a small wattage tube amp for entry into the Cal State Fair this summer '15. I like the idea of showing the public that you don't need massive Wattage to have a great sounding system with hi efficiency speakers, which one of the other students is building. I've only taken a few classes but my instructor said that I will learn more than I could from most books by building a tube amp. I've looked around and saw your Budgie SE and thought it would be a perfect project but I was questioning whether it would be a better learning experience to P2P the amp rather than just assembling the parts. Does doing P2P teach me more than just solder techniques or is it best to just go with a circuit board on my first project.

I have until the end of May to complete so theres plenty of time. Is this a good idea for a new student, and if so, what would I need besides the schematic & parts list?....and are all the parts readily available? I was not going to go very high end on the transformers since I would be using this primarily to drive an ipod, are Hammonds good enough to use?
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Re: First Budgie SE (Single-ended EL84 amp)

Postby mike567 » Fri Jan 23, 2015 2:08 pm

Unless you already have the transformers use the specified ones. Hammonds are twice the price. The Edcor are very hard to beat for the money. They make 3 grades so take your pick.
The downside.... It usually take 4 to 5 weeks to get them.
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Re: First Budgie SE (Single-ended EL84 amp)

Postby battradio » Fri Jan 23, 2015 6:08 pm

http://www.transcendar.com/2.html

This would be another choice of output transformer if time factor is important
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Re: First Budgie SE (Single-ended EL84 amp)

Postby perkinsman » Mon Jan 26, 2015 12:54 pm

How do I know what size transformer to buy?

I'm also trying to get a fix on the total costs involved here. Is the total cost the Budgie kit plus the transformers or are there add'l costs?

Also, from a learning experience, would there be any value to P2P the amp rather than just assembling the parts? Does doing P2P teach me more than just solder techniques or is it best to just go with a circuit board on my first project?
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Re: First Budgie SE (Single-ended EL84 amp)

Postby Shannon Parks » Tue Jan 27, 2015 6:38 pm

Finally have the new manual (purple Rev A) and BOMs up here:
viewtopic.php?f=21&t=6547

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