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My first DIY tube headphone amp - 12AU7 / 12BH7 with all Hashimoto transformers......

post #1 of 7
Thread Starter 

Soooo – I’ve been a lurker here for about 5 years.  Bought some headphones on the classified section, but this is my first post here ever. I spend most of my forum time on other sites (Mercedes Diesel forums, Photography forums).  Now’s the time to make my debut.

 

About 6 years ago I began this project, a friend made me a schematic, and bread boarded it.  I bought all the parts, started the fabrication, but then life got in the way; we moved across country and back 3 times (I'm in the Army National Guard) - now I am finally getting back to this.  I have many tube amps, all hand made by my friend Don Allen, from Phoenix, AZ, but I have never built anything myself.

 

 I hand built my 100K step attenuators (ladder type) out of a pair of 48 step Daven shells I got off eBay. 

 

The resistors came from a factory in Iowa. I bought three of each value and kept the two that were the closest.   I wanted a volume control for each channel.

 

 

During assembly I clamped it into a small vise. In this photo I'm almost done with one side.

 

I never get tired of looking at these, they came out sooooo nice.  All of the contacts were heavily coated with silver, and the main tie cable is actually solid silver wire.

 

 

 

I am now wiring the tube sockets together, following the schematic my friend made for me.  It’s a real challenge, actually looking at this paper and deciding on how to physically wire stuff together,  not knowing if the way I’m doing it is the right way or not (even though the logic is right there on paper, I’m sure there are a lot of things I’ve done wrong so far).  I have been reading whatever I can find online by Susumu Sakuma. He has some great tips for earth ground and signal ground that I’m going to try to employ.

So, here is what I've done so far - the power supply is all together and working, 5R4WGB rectifier for the 325 Vdc (regulated via a Welborne labs kit) - the 12.6 filaments are heated by another Welborne Labs kit. Fit it all into one Bud box, along with a Hashimoto power transformer and a Hashimoto 15 Henry choke.

 

All 4 front end tubes with their filaments ON !!!!

I have two lamps on the power supply.  One indicates that power is applied, the other blinks while a timer counts down from 60 (at which time the B+ voltage is actually switched onto the plates).

 

I still have a few parts on order, they’ll be in this coming week.  I’m hoping to have this running before the end of the month.  For now it will have only one input, for a CD player.

 

I'll work hard to keep this posting updated, as long as anyone is interested.  Thanks for looking !

post #2 of 7

Looks stupendous!!

 

Why in the world are you posting it in a forum section where the majority wants $100 amps that they can claim are the end game?

 

Please ask a mod to transfer this to the DIY section. :) 

 

P.S. Love your use of PRP resistors in those attenuators. ;)


Edited by tomb - 1/19/14 at 4:12pm
post #3 of 7
Thread Starter 
Thanks for the complement, Yes, PRP was real easy to work with and I really like that they are from the Midwest (I'm originally from Kansas).
post #4 of 7

WOOOOW!! thats one intense build.  I love the dual volume pots on my darkvoice amp.  I end up using them a lot, specifically for live recordings where the mix balance can go back and forth from right to left with different tunes and musical passages.  I am surprised more DIY builders don't use this configuration.

 

(Stupid question warning)

Are those EL84s?

Is this design (basically) a low wattage speaker amp, but with output transformers selected for higher impedance loads?

What resistors are you using in the tube power section?  These suckers get blazing HOT in my darkvoice.  I am using small PC cooling fans to vent the chassis, but they are really noisy and detract overall from the whole listening experience.  I'd love to see your cooling/venting method for those guys.

 

Impressive 6-year project you've got, good luck on the rest of the build!!


Edited by kramer5150 - 1/21/14 at 9:35am
post #5 of 7
Thread Starter 

Howdy and Thanks !

 

Nope - they're 12AU7 and 12BH7 (one feeding the other, then into the Hashimoto HL-20K-6 Line Input/Output trannys).  I am following the schematic that Isao Asakura drew for me (at Sound Traditions).  He was really cool to work with.    As for the resistors in the output section, I haven't finished that part yet (I just ordered all of the final resistors from eBay and should get them next week - mostly 5 and 10 watt examples, including a quad of gold bodied Dale 5K 10 Watt resistors).  Everything in the output section is slightly oversized - to help with the heat.  There will be no other special cooling applied, just gonna let it all get hot (just like in my SET 2A3 amps).

 

I forget where I found the case. I have seen someone else on the DIY section that has the same brand.   The power supply cabinet is a vintage Bud Box that I bought on eBay (actually scored a mint in the box pair of these which are painted in a cool grey hammertone). All of the metal brackets and mounts I fabricated (crudely) from parts I had laying around or found at the scrap yard.  By the time this is all done, it will be so dirty from sitting that some will mistake it for a 60 year old amp that spent it's life in the Abby Roads studio.  Too bad I'm not a cigerett smoker - that would really make it look like vintage gear.

 

So far this project is all show and no go.  Untill I do the final smoke test and then plug in my sacrafice pair of cans to see if it works,  I won't be making any promises.  This is my first complete build. I've helped build some things, cloned others, and repaired some of my own stuff,  but never actually done the whole thing by myself.  Everyone here will get to see me sing or cry (laughing and crying, isn't it all the same anyway?) Forgot who sang that line,  maybe Joni Mitchell - but it applies here I think.

post #6 of 7
Thread Starter 
Just figured out that I got the amp cabinet from Par-metals. Saw someone else here that was using one of their cases.
post #7 of 7

Could you post a schematic? 

 

I am always curious to see what other people are building & designing. 


Edited by nikongod - 1/23/14 at 6:32am
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