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DIY portable tube headphone amp? - Page 2

post #16 of 25

Nixon,

I definitely want to see pics of your project!!

 

I broke down and bought one of the 6418 lots from eBay:  

 

http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&item=200736121697&ssPageName=ADME:L:OC:US:3160

 

Yesterday I pieced together a BOM from Mouser:

 

http://home.earthlink.net/~morgan.whitney/images/K272A.pdf

 

I'm interested in opinions on the upgrades, and I'd be grateful if y'all would double-check my components.  

 

I decided to go with Nichicon Muse Gold for all caps.  Output caps upgraded to 1000uf and input caps to 1.0uf WIMAs (an idea from Fred_fred2004 in this thread: http://www.head-fi.org/t/522639/oatley-k272a-build).  I also added another pair of 1.0uf WIMAs to use in parallel with the output caps.  

 

I'm a bit frustrated with the L4949 IC, it appears that no one (Mouser, DigiKey, Newark) has it in a dip-8, only in surface mount.  I know how to solder and have a good iron, but soldering smd seems to be another level of skill (that I'm not sure I've attained yet).  

 

I'm also unsure what to do about the trim pots since I'm looking to make this a portable amp.  Can I eliminate the pots entirely and go with the stereo pot I have in the cart, or do I use the trims AND the stereo pot together?  If so, how do I wire them in?

 

 

post #17 of 25
Thread Starter 
Quote:
Originally Posted by bengoshi2000 View Post

 

I'm also unsure what to do about the trim pots since I'm looking to make this a portable amp.  Can I eliminate the pots entirely and go with the stereo pot I have in the cart, or do I use the trims AND the stereo pot together?  If so, how do I wire them in?

 

 


As far as I can can tell you should be able to bypass the trim pots and use a stereo pot instead. 

 

 

As you're trying to make it as small as possible, you might want to hunt down the schematic for the first version of this amp that didn't have the 2 AA batteries and used the 9V battery for the tube heater. Battery life takes a knock but should make the amp smaller. 

 

post #18 of 25
Quote:
Originally Posted by Nixon View Post

As you're trying to make it as small as possible, you might want to hunt down the schematic for the first version of this amp that didn't have the 2 AA batteries and used the 9V battery for the tube heater. Battery life takes a knock but should make the amp smaller. 

 

 

I did take a look at that, but IIRC, it used 2 9volts in parallel... not much difference in size/weight.  :/

 

Right now I'm thinking of going with a pair of AAAs (LR03) for the heater circuit and a 12v keyless entry battery (http://www.amazon.com/Energizer-A23-Battery-12-Volt/dp/B00004YK10) for the main.  Seems like there was some discussion in the main K272A thread that moderately higher voltages could work.  Now whether these A23 (or similar) batteries could drive the amp remains to be seen.  I imagine that battery life will take a hit.  Perhaps a pair of A23s in parallel... hmmm...

 

 

 

post #19 of 25
Thread Starter 

Or you could use a voltage regulator to bring the 9 or 12v supply down to the 3v needed for the heaters. 

post #20 of 25

Welllll...

 

I could put the design of the hybrid portable out there, as there are no plans to do anything similar.  At least for now.  However, since it uses all SMT components and a fairly complex power supply (buck regulator to get the filament voltage and a flyback to get +/-24V from a single Li+ battery), not sure it would be a practical DIY project.

 

But at least I can offer up my experience:

 

I tried almost every battery tube out there.  Almost all of them (well, the ones that have directly-heated filaments of less than 3V) sing like mad.  The 6418 is one of them; works great other than the singing.  BTW, if anybody needs some, I have 20 that I have no use for... send me a message, maybe $5 each?

 

The best tube I found as far as being quiet and still having low filament power was the CK534AX, which was used in the hybrid.  I bought up all I could find, and there are very few around now.  Though you never know what might pop up out of some warehouse someday.

 

Though a tube is certainly a novelty, maybe a single-ended JFET stage is more practical.  You can get a JFET circuit to sound and measure an awful lot like a SE tube.

 

Hmmm, maybe THAT should be a new project.  Like I NEED another project.

 

Pete

 

 

post #21 of 25
Thread Starter 

Thanks for the input Pete.

 

Mainly making it tube powered so I can get use to working with tubes, will have a crack at a Starving Student after this one. 

post #22 of 25
Quote:
Originally Posted by pmillett View Post

Though a tube is certainly a novelty, maybe a single-ended JFET stage is more practical.  You can get a JFET circuit to sound and measure an awful lot like a SE tube.

Might be useful: http://www.radiomuseum.org/forum/the_trioderizer_a_solid_state_triode.html
post #23 of 25

 

Quote:
Originally Posted by Nixon View Post

Mainly making it tube powered so I can get use to working with tubes, will have a crack at a Starving Student after this one. 


Just build the starving student. Its fun, easy, relatively safe, and well documented. 

 

Building a portable tube amp combines all the challenges in building a tube amp with all the challenges of building a portable amp WITH challenges that are unique to a portable tube amp.

 

The problems & solutions in portable amps and stationary tube amps are well documented all over the place. People have been thinking about & solving these problems pretty much forever.

The problems & solutions in a portable tube amp are not so well documented. If your comfy figuring out how to solve a problem you may encounter on your own, go for it. If not stick to well documented projects where you are less likely to have problems. 

post #24 of 25
"Portable" probably means different things to different people. For me, I want an amp that's easily moved, but I don't plan on using it while in motion. I love my Starving Student, but I do get tired of lugging it from room to room. And clearly I couldn't use it in the vanpool on the way to work. biggrin.gif.

I'm also keeping my expectations in check... this project won't rival the sound of my Starving Student, I'm sure.

At the end of the day, I just want to see if (considering my minimal skills) I can build something that works!
Edited by bengoshi2000 - 4/3/12 at 4:40am
post #25 of 25

hmm i went around looking but never found anything about using the 6111. Is it possible to recreate the oakley k272a circuit for the 6111. Also what's the diff between the 5pin of the 6814 and the 7 or 8 (not sure) of the 6111?

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