My new tube preamp build

PWRRYD

Hi guys.  It's that time of year again when it's getting colder outside and my DIY interests shift towards vacuum tubes...

I definitely don't need another tube amp.  Actually I don't really need another tube preamp, but they are fairly cheap and LOTS of fun to build.

A couple of years ago when I was at DIY S. Dakota I bought some old tube stuff off the swap meet table from Mike Jennings for only $5.  Turns out I got a very nice power transformer, a pair of cool vintage smoked glass 6V6GT tubes, a multi-section high voltage cap, and a decent 5Y3 rectifier tube.

Over at diyaudio.com there is an epic 6V6GT line preamp thread from a guy named Salas.  I have all the parts to build this design, sans the miada regulators. That doesn't bother me at all.  I like to keep tube circuits as simple as possible and feel they sound just fine or better that way.  So my power supply will be more my design.  Otherwise the basic circuit is his design.

I will post a butt load of build pictures here along the way.  I bought a nice hickory board today that has a ton of grain!!!  That board and a piece of 0.0625" aluminum plate I have will form the case.

More to follow Gents.

Tom_S

Cool! I never would have thought to use a 6V6 as a line amp. I just starting looking a that thread - are you doing the single stage triode wired version, or is there something more complex in the upcoming pages?

PWRRYD

Single stage, common cathode, triode wired.

Kornbread

   Plenty of pictures and simple explanations for dummies please.  I'd love to try and build this.  

PWRRYD

Yes for sure Kornbread.  I will take many pictures along the way with construction comments and answer any questions.

The great thing about many tube projects (like this one) is how simple the circuits are with only a few resistors and maybe a capacitor or two per channel.  Honestly they are no harder to construct than a 3 way passive speaker crossover.  That said, they do involve high voltage, high enough to kill you.  So proper fusing, grounding, and basic common sense are manditory.

I plan on designing my layout this weekend and will post those drawings.  This preamp could be build very compact, but because this is DIY (no commercial restrictions) I will build it jist as large as I need to.  That will allow me to keep very generous spacing between the noise generating power supply parts and the very sensitive small signal audio components.

ani_101

Hi Craig, what would be an approx cost be, with reasonably good components?

Tom_S

I just saw the schematic for one that uses the screen as the output. That one sure is twisting my brain....

PWRRYD

Good question Ani.  Let me do a quick survey BOM.  Off the cuff I'd guess around $200 max.  The nice thing about tube preamps vs tube amps is the preamps don't need the heavy and expensive output transformers or large power transformers or big output tubes.  These 6V6 tubes are only about $20 each (one per channel).  These are supposed to sound very nice:

https://www.tubedepot.com/products/tung-sol-6v6gt-new-production-power-vacuum-tube

ani_101

Great, thanks Craig. Guess I should start out with a pre amp before going the amp route....

PWRRYD

Tom S brought a very nice tube preamp to Iowa.  Unfortunately we didn't get a chance to listen to it.  I bet it sounds very good using 12BH7 tubes.  Tom, what would you guess it would cost to build it?  Maybe $125 or so?

Tom_S

I think you're in the right ballpark. I would have to price out the parts, since almost everything I used was surplus or salvaged from old tube gear.

Kornbread

   Yes, a BOM and a good parts source would be most excellent.  Will this be one of those we can roll a number of different tubes in?  

PWRRYD

You certainly can roll different brands of 6V6 tubes.  Some new production tubes include:

Electro-Harmonix
Genalex-Gold Lion
JJ Electronics
Tung-Sol
Mullard
Telefunken Black Diamond

These range from $14 - $40 each.

Then there are NOS (New Original Stock) tubes like RCA, Sylvania, Bendix, National Union which range from $60 - $250 each!

But this circuit is only optimized for 6V6 tubes.  Other tubes like the 6L6, EL34, etc. have the same octal base and may work in this preamp, however, the circuit values are not optimized for their tube curves.

PWRRYD

I will be building a prototype first to dial in my power supply part values.  I have a thrown together wood case with a sheet metal top plate that has several octal sockets.  That way I can build the final preamp and not have to solder and unsolder any parts.  Much easier to end up with a very clean build that way.

PWRRYD

I tried an "inlay" for the first time.  This is my 4" hickory board, with a 7/8" wide, 3/8" thick inlay of mahogany.  Pretty happy with how it turned out so far.  It still needs a lot of sanding after glue up and before finish.

Tom_S

Sweet! That should be your signature look for all your tube gear builds in the future.

Bryan@MAC

Bud, that's amazing....and please elaborate on that bench??  

PWRRYD

Bench?  You mean my rolling table saw which I do use as a bench?

S7910

I'll second the request for details on the rolling table saw / router table / bench combo

Bryan@MAC

PWRRYD said:

Bench?  You mean my rolling table saw which I do use as a bench?

Yes, that's what I meant:  The rolling table saw/router table/bench thinggy.  

PWRRYD

It all started with a $40 craigslist find, an old cast iron Craftsman 10" 3 HP table saw.  I called the guy and he said it had been in his father in law's leaky shed for longer than he could remember and that it was pretty rusty.  I went to check it out and discovered that it was all there, with a newer looking motor and the rust was only surface rust on top of the table.  It cleaned up nicely.

It didn't come with a stand, and since my work shop is my garage and driveway I built an over sized base out of left over 2x4's and plywood.  I bought some nice swivle casters with brakes.

A couple years later a guy at work sold me that cast iron router table for $75.  I had to drill new holes but it lines up perfectly and gives me even more table top area.

A couple years ago I so sick and tired of the wimpy Craftsman fence.  I found a floor model Sawstop fence at Woodcraft and got it for half price.

I keep the top clean and waxed and the saw alignment is dead nuts.  It is soooo much more fun to cut panels with a saw that has a perfectly parallel fence.

MartyH

"It is soooo much more fun to cut panels with a saw that has a perfectly parallel fence." 

I wonder what that's like.

Kornbread

   While we're on the subject, my sliding compound miter has never made a perfect 90* cut.  It's just enough off to be a problem. The longer the cut, the worse the problem.  Is there a way to true these things up, or is being a little off, to be expected?     

PWRRYD

I would think you should be able to dial it in.  I don't use my compound miter saw for that though.  I tilt my table saw blade 45 deg and push the pieces through with my sliding miter.

PWRRYD

Hey guys, just a quick little project update.  The power transformer I salvaged from the gear I bought was a pretty rough looking with gunk and bruises.  So I took it to work today and lightly blasted it then hit it with a couple of coats of high temp engine paint.  Here is a picture of it mounted to my prototype rig along with the tube sockets and tubes installed.  I think those Tung-Sol smoked glass 6V6 tubes look totally B/A!  The final (real) chassis will be 2 inches narrower and 2" shallower.

 

dynamo

Transformer really turned out nice! 

D1PP1N

Kornbread said:

   While we're on the subject, my sliding compound miter has never made a perfect 90* cut.  It's just enough off to be a problem. The longer the cut, the worse the problem.  Is there a way to true these things up, or is being a little off, to be expected?     

Ive been using this with success to calibrate my (90deg) stops or the zero on my tablesaw. It works for all angles. In increments of like 0.1 i think. 

 Calculated Industries 7434 AccuMASTER 2-in 1 Magnetic Digital Level and Angle Finder / Inclinometer / Bevel Gauge, Latest MEMs Technology, Certified IP54 Dust and Water Resistant https://www.amazon.com/dp/B0148M7P4O/ref=cm_sw_r_cp_apa_62zbAbK0V3NQY 

You put it on the tabletop of your tablesaw or miter saw and "zero" it. Then put it on your blade and set it to whatever angle you want. You would be surprised how many times your off by 1 deg. 

Just some random tips but if you cut a 45 cut one edge on the left of the blade and the other on the right side it should always add up to 90 again even if your off. 

The trouble with compound miter saws is that they always have flex when they are fully extended out. You can pull it outward all the way and apply sligjt pressure in either left or right direction and watch it deflect a little. I try to start the saw in the fully inward position and when you extend it outward try to use a soft touch so you dont apply pressure to one side and proceed with the cut. 

Bryan@MAC

That AccuMASTER toy is going on my secret Santa list....nice.  Thanks.

PWRRYD

Excellent info Mike!  Thanks.  I'm going to order one of those Accumasters.

D1PP1N

No problemo! I had to buy it when i bent my angle guide on my table saw. I was stacking all my cuts below me against the front of the saw. I then finished and set it back to zero but it was harder to turn. Turns out a board got wedged between the handle and the pointy angle guide and bent the shit out of it lol. 

Ron_E

When I need an accurate 45 degrees I take apart my metal combination square.



Ron