I want to build a tube amp

I've been lurking over on head-fi for almost a week now, its just the last thing I need is to join another enabling group, err, forum. The Millet looks to be my ideal shot for a first tube build, but after a bit of searching the 19j6 tubes are scarce! There are a few old repair shops still around town I plan to investigate tomorrow, hopfully I can score a couple pairs. If not, then I guess I'll do the work around design on the Millet for the 12AU7 tubes, those are easy to find.


Still open to ideas for other simple inexpensive tube designs, but the Millet Hybrid looks like the best candidate so far.


-Xander
 
Enabling group is right. :/ Sorry about your wallet.

If you don't want to bother with the work around, decent 19j6's are about $8 at ESRC (if they actually have them in stock, anyway) - because it's a mosfet tube follower, this design doesn't benefit as much from tube rolling as some do.

There is also a somewhat easier conversion to 12SR7 tubes, using an octal socket. I think Logistic at Head-fi wrote out the conversion details.
 
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Yeah, I found them at VacuumTubes.net for $10 ea. Couldn't find them at RadioDaze though. Fleabay seems to have the highest prices! I saw some for $20, untested unmatched!!

From the reading I have been doing on this amp, tube trouble shooting seems the default. I have only seen mention of the 12AU7 work around, haven't found the details about it yet. I will look for the 12SR7 details as well.

I am finding out that I really need to brush up on my print reading! Circuit diagrams are still a bit intimidating, lol! I guess I have forgotten more from my drafting days than I remembered! Its coming back slowly though.


-Xander
 
Found it, copied from this thread - http://www.diyaudio.com/forums/tubes-valves/142000-19j6-replacement.html :

I wanted to modify the starving student amp using an alternative tube to the scarce 19J6's. I finally settled on the 12SR7 and 12SW7 which are only $1 each at vacuumtubes.net. Perfect for the starving student. The caveat is that they are metal tubes and some people may prefer glass tubes. In that case the 12SR7GT is the glass tube version of the 12SR7. It is a few dollars more per tube but still cheap.


Here is the result, the metal starving student:


If you want to build this version, you have to make some small changes -

R1/R7 - 44k
R5/R11 - 4K
R2/R8 - 330K
R4/R10 - 180K

You will have to use an octal socket, and here are the conversions from the seven pin socket in the original circuit diagram:

1,2 -> 6
5,6 -> 2
3,4 -> 7,8
7->3

You will also have to ground pin 1 which is for the metal casing. It is probably a good idea to ground pin 1 with a separate path to ground from the heaters (pins 7,8). That way if the ground connection for the heaters breaks for whatever reason you don't see that voltage on the tubes.

Using 2" heatsinks is also recommended since the heaters are running at 12V instead of 19V.
 
Liamstrain, cool, thanx! I made a few phone calls to the local repair shops but no luck in finding the tubes. I always like to check locally first before ordering. I will check with the spot that FBC recommended though.

I will make some notes on the print for the SSMH and a second parts list.

Ugh, I stubled across a thread on Head-fi about making custom wood cups, I already have a couple wood lathes and some very nice woods. Someone shoot me now! I gotta try it out! Maybe a set completely from scratch, minus the drivers....

Anyone have a really good scripted apology to a wife I can use?! :p


-Xander
 
They can tell when it's scripted/rehearsed. Heartfelt and improvised is the only way to go.

Sorry about your wallet.

I sent you some info via PM, but just thought of another track you could go. Get a pair of used/beat up Grado SR60 - build a custom set around them - order a set of replacement pads (I prefer the bowl pads that come on the SR125 and above, they cost the same). Then when you scrape together the extra dosh, you can get the Grado Magnum drivers and do a swap down the road. the 60s are no slouch to begin with, and that would be a fun project to pair well with the Millet amp.
 
I ordered a PCB for the Starving Student Millett Hybrid amp based on 12AU7 tubes! I'll make up a tweaked build list with slightly upgraded components from the basic list.

I was really considering going with point to point wiring, but the simplicity of using a PCB really eliminates issues. Also, much easier to build an enclosure around a board than to try and stuff things into a box and hope nothing shorts!

Next I will get the tubes, heat sinks and power supply. I think I will order 4 tubes to have spares and hopefully get matched brand tubes.


-Xander
 
interesting - I like PTP, but a board does simplify things, especially if doing a modified circuit.

I really like vintage 12AU7's - I've got some old globes, rca's, and Mullard's I love (running a Dumont, currently too). All of which can be purchased for less than one vintage telefunken.
 
Yeah, I figure I can get my feet wet with this and then do a ptp amp next. Plus, the board was only $6.75 shipped from AUS.

Will update as things go.


-X
 
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