[bengoshi2000]

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?
 
 

 

[Nixon]

Quote:

 
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. 
 

 

[bengoshi2000]

Quote:

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...
 
 
 

 

[Nixon]

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

 

[pmillett]

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
 
 

 

[Nixon]

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. 

 

[dsavitsk]

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

 

[nikongod]

 
Quote:

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. 

 

[bengoshi2000]

"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. .

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!

 

[mfm123]

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?

 

[Pietrone]

I've been messing about with the fa shmidt version, the aim being to get it into an altoids tin this is what I have so far



Obviously toner transfer





Notice the heatsink has changed orientation in the final version, it is just warm to the touch using 12volts so I think it will be fine in a tin

I used a 12AU7 and a JRC4556

sounds very nice for a simple project

If anyone wants the layout to try their own just drop me a PM I use pcbartist (cos its free)

cheers
FRED

Hi Fred
id love to try please!

moreover, I don’t know anything about electronics, would you guys be able to share good sources or at least list the concepts I need to understand? Thank you If you do!

 

[tomb]

Hi Fred
id love to try please!

moreover, I don’t know anything about electronics, would you guys be able to share good sources or at least list the concepts I need to understand? Thank you If you do!

Pete Millett's website on books has all you need to know: http://www.tubebooks.org/technical_books_online.htm . He posted in this thread, btw.

As for Fred, he left the business several years ago. I doubt you will find anything from him these days.

 

[Pietrone]

Pete Millett's website on books has all you need to know: http://www.tubebooks.org/technical_books_online.htm . He posted in this thread, btw.

As for Fred, he left the business several years ago. I doubt you will find anything from him these days.

Pete Millett is the man! he left a treasure there.

Tomb, thank you so much for your help! Appreciate it