New Crack planning

[ALL212]

There are many posts to go over and I'm hoping for some clarification. 

I'm going to build the next Crack and Speedball with a 6SN7 instead of the 12AU7 and it looks like this is just a different socket with wiring changes with no change to components.  Is that true?  I did find this:

12AU7 Pin  wired to 6SN7 Pin
    1                            2
    2                            1
    3                            3
    4                            7
    5                            No Connection
    6                            5
    7                            4
    8                            6
    9                            8

Is there any rewire/changes needed to optimize running the 5998 tube?

Thanks.

 

[ALL212]

Guess I have to pay the piper.  Here's a pic of the plan and parts acquired so far.  It's not out of perspective either!

 

[mcandmar]

Nice collection of parts you have there

A 6SN7 and 12AU7 is essentially the same tube in a different bottle, only real difference is the heater wiring. If you download the datasheets for both and you will quickly figure it out.

 

[Doc B]

A 6SN7 and 12AU7 is essentially the same tube in a different bottle, only real difference is the heater wiring.

Yeah, not exactly. The 6SN7 is more linear, can take higher voltages. It's a somewhat different tube with a similar mu. Closest 12v 9pin tube to a 6SN7 is a 12FQ7 - which won't work in a Crack because it has a 12V (300ma) only heater.  But you can mod a Crack to use a 6SN7 instead of a 12AU7 without changing the op point.

 

[mcandmar]

Interesting, i didn't know they were more linear, i just assumed they were a direct successor similar to the 6F8G to 6SN7.  I guess that explains why i always preferred them over the 12AU7s. The tube i liked the most of the 9pins was the 6FQ7/6CG7, which i assume is just a 6volt version of the 12FQ7.

Come to think of it i dont really like 12au7's at all, i've used them in a number of mock ups and didn't keep any of them.

 

[ALL212]

More parts in.

I traded out the big blue Clarity caps in my existing crack for a pair of Audynes so I could use them in the BAC.  Tipped the Audynes with some 1uf Sonicaps.

Will tip the Clarity PX's with a pair of 1uf MR's.    The big kid in there is a 220uf Solen for the PS.

 

[JamieMcC]

Looks like a lot of fun in the making. Where did you find the little pcb board for the rectification diodes?

 

[Hornet900]

Jamie

I have a spare pcb board for the rectification diodes that I just got from partsconnexion.com .

its a little shorter on the left side than the picture above where its been cut  so maybe tricky to drill the  hole for mounting but its the same size the other guys have

pm your address if you want it i@ll send it free mate no charge  :-*

 

[grausch]

Regarding the rectifier pcb, no need to drill any holes in there. Lee Haskins just used 18 awg to hold them in position - http://bottlehead.com/smf/index.php?topic=7787.0. Quite nice the way he placed everything.

However, I was really not really comfortable doing that, so I used a zip tie mount and a zip tie to hold it in place. Combined with 18 awg, it does not move. Pictures can be found here - http://bottlehead.com/smf/index.php?topic=7945.msg77011#msg77011. The second picture gives a nice view.

 

[Hornet900]

thanks grausch

I already seen your pictures thanks    I did read the wire could hold it mate thank you

I've not installed my pcb rectifier yet as my amps stripped down I'm  rebuilding it. 

I was going to get my top plate powder coated but changed my mind ,  yesterday  i cleaned the top plate and  sprayed  clear gloss lacquer on top and sprayed the bell and transformers plates black

looks nice just waiting for it to dry now .....My  top plate was a bugger to keep clean with dust should be better now    . Waiting for parts  to start

 

[caffeinator]

Hi ALL212,

Great looking project!  Is BAC = Big Ass Crack?  Where did you get (or will you get) the top plate?

thanks,

David

 

[ALL212]

Got lucky on the PCB - it's still got a lip on it.  My original crack has a standoff glued to the top plate but I can't get anything to stick to the PCB.  The 18g solid core wires hold it just fine.

Front plate express should be able to do this.  I'm cheating - I work at a steel/aluminum distributor and we've got a laser burner.

Yep - BAC is Big Ass Crack...gotta get a label for the base with that on it..

Does anyone know if it hurts to mount a cap on the top of the plate next to the transformer? 

 

[caffeinator]

Hi there,

Thanks for the info; looks like a great build and fun project.

As for caps on the top plate; a question and  some comments.

So, the question is what sort of a cap is it?  A PS cap or something else?  If it's a power supply cap, that's not unusual; a lot of tube amps have a 'Cap Farm' sitting near the Power XFMR and near the PS choke, sometimes betwixt the two (take a look at, say, a Dyna ST-70, vintage Marantz Amps, lots of SE amps - there are caps jutting out of the top plate right by - albeit an inch or two away from - the power XFMR).  That it's such a common practice suggests to me it's not altogether bad though I don't know if a headphone amp sets a low enough noise threshold to make a difference.  Breadboard it and see, perhaps?

The comments are that for some caps (say, the Jupiter wax/foil caps), if the power XFMR runs hot, the heat exposure might be a reason to relocate, as might the presence of high voltage on exposed wiring, depending on how well insulated or concealed from inadvertent contact it happens to be.

 

[ALL212]

You're right, just not thinking through it.  I've seen the Dyna and the caps are right there on top.  These are the power supply caps I'm thinking of mounting on top so there is even more room underneath.  That big Solen will be the last PS cap.  The big glass tube is a cap to tip the 2nd PS cap with.

I'm not going to run any caps that should be affected by heat so this should be ok.  I just have to figure out an attractive way of doing it.

Thanks, appreciate the input.
Aaron