Crack with 12AU7 or 6SN7 to start?

[dludingt]

Hello all,

I plan on purchasing a Crack+Speedball later this summer and wanted some quick feedback about driver tube choices. My dilemma is that I have a great stash of both types of tubes mentioned in the subject. I have Telefunken, Mullard (shield), Amperex Bugle Boy, and various American 12AU7s on hand, and RCA smoke glass VT-231s and some great Sylvania brown base 6SN7 tubes. Which should I start off with? I will be using HD-600's and like a rich, punchy sound for my listening. I'm thinking the 6SN7 would be a good choice, soncially for my listening tastes.

My first inclination would be to punch out the driver hole to accept an octal socket for the 6SN7 right off of the bat, then purchase an adapter for the noval sockets. Going from a larger to smaller socket seems like it would be the lower noise choice.

Does this sound like a good idea?

[Grainger49]

The answer is to build stock first.  Then you know what any modification brings to the table.

[dludingt]

Thanks for the reply. I have some experience with working on point to point amps (having restored some HH Scott equipment a while ago), and wanted to know how difficult it would be to make a socket swap after building stock? When I worked on my vintage equipment, I was never working on more than one or two tube pins.

For those that have made a socket switch, how much work was involved in this?

[Tubejack]

I built a Crack/Speedball with various sundry "upgrades".  ("Upgrades" is such a subjective term.  Yes, I have changed in a Goldpoint attenuator, added a PS choke, Mcap silver oils, etc.. How much any of those effect the sound is such a personal subjective opinion ..... more expensive components don't always equate to "upgraded sound" .... but I digress).  I have a personal tube stock similar to yours, and have been using an octal to 9-pin adapter for 2+ years.  I like the flexibility to go between types.  I have favorite flavors in both pin-outs.  I feel a properly wired and constructed adapter with good quality sockets and wire (I built my own adapter, but there are well made adapters on eBay) doesn't significantly effect the sonics for me to commit to a specific tube pin-out type.

[dludingt]

So, the issue with the adapters on eBay (from China) is that they use too cheap of material? Where would one find the parts for that? I'd imagine it would be easy to find a PCB mount octal socket, but what about the noval pin base?

[Paul Birkeland]

We suspected that the issue was that the heater wires weren't twisted and/or shielded.

I proposed a simple experiment to determine if this was the cause, but nobody seemed all that interested in trying it out.

-PB

[mcandmar]

That is interesting because i had no issues whatsoever with the adapters i made for my S.E.X. amp, i was half expecting it from seeing comments from Crack and Woo owners who have used them. Though it is a DC supply vs the Cracks AC...

[dludingt]

I work in lighting controls and for the any sensitive information, we always have to use twisted, shielded pair wire so Paul's observation makes sense. That would keep out any interference or noise from interjecting a hum into the signal from the noval socket to the octal.

I was planning using that kind of wire for everything in a theoretical adapter. So, where did everyone find the noval pin base to go up to the octal socket? My quick online searches haven't shown anything yet...

[dludingt]

Nevermind - I think that buying a noval socket saver and taking the screw out should give me the correct base to connect an octal socket to. https://www.tubedepot.com/products/9-pin-socket-saver

[Paul Birkeland]

I was planning using that kind of wire for everything in a theoretical adapter. So, where did everyone find the noval pin base to go up to the octal socket? My quick online searches haven't shown anything yet...

Be careful with that philosophy, as you don't want to to twist a grid wire together with a heater wire. 

[rlyach]

Here is the 9 pin socket saver opened up. Be sure that this is what you want. I have used these in the past but not for building an adapter. 

[Tubejack]

You could use one of these.

http://www.ebay.com/itm/4-pcs-CMC-9-Pin-Tube-Socket-PCB-Adapter-12AX7-EL84-/140343010840?pt=Vintage_Electronics_R2&hash=item20ad186618

Solder the socket saver (as it has long pins) to the PCB and use the outer pads to connect short leads to the octal socket which would be positioned above.  That assembly could then be fitted into either a short length of PVC or copper tubing  (I used a copper tube plumbing short piece from the plumbing section of Lowes, with an appropriate inside diameter to accept both the PCB and the octal socket, cut to 1.0 -1.5" (as needed) with a hacksaw and de-burred with a file).  I used 2 part epoxy to hold the ends in place.  The advantage of a copper sleeve is it could be grounded if you felt the small length of leads needed to be shielded from RFI.  (I have not found it necessary.)  A similar device would be this on epay .....

http://www.ebay.com/itm/1pc-6SN7-6n8p-CV181-TO-12AU7-ECC82-tube-adapter-6-3V-CNC-Copper-body-/201094586373?pt=US_Home_Audio_Amplifiers_Preamps&hash=item2ed22be005

[dludingt]

Be careful with that philosophy, as you don't want to to twist a grid wire together with a heater wire.

My tentative plan is to use a twisted shielded pair of thin 22awg wires for each pin (doubling up for the heater from 12AU7 to 6SN7).

What about getting one of the socket PCB's and a socket saver, soldering the pins to the standard tube depth (will have to measure) on the PCB, then clipping off the top end of the socket saver? That would leave me with a PCB with the correct length tube pins and an easy place to solder my wires to the octal socket.

I was also thinking of then making a mold for the whole converter and then filling the space between the noval and octal sides with a potting compound to decrease any potential for microphonics or vibrations. I could then add some kind of cover, whether it's copper pipe or something else.

Does this sound like it would work well? Funny how I'm planning this far more than my actual Crack build.

[rlyach]

That might work if you are careful. I have worked with these pin savers before. As soon as you heat a pin to solder it, it comes loose from the socket. The pins are only soldered to the socket and come off easily. Using a PCB will make it easier. You could just start with the correct diameter pins, cut them to length, and bend a loop at the top to solder to. Then insert the pins through the PCB and solder. You could also use a 9 pin socket to hold the pins in place during soldering. That way the pins will all be in correct alignment. Simply put the pins through the PCB and insert them into the socket and then solder to the PCB. Attaching the octal socket could be a little tricky because octal tubes have a center alignment post. You may be able to get a insulating tube of the correct diameter and glue the octal socket to the tube, solder the jumper wires, and then glue the PCB to the other end of the tube. Just food for thought.

[Tubejack]

Funny how I'm planning this far more than my actual Crack build.

Actually, if I was to do it again, I'd probably try one of the many available on epay.  http://www.ebay.com/sch/i.html?_trksid=p2047675.m570.l1313.TR0.TRC0.H0.X6sn7+to+12au7+converter&_nkw=6sn7+to+12au7+converter&_sacat=0&_from=R40

Between this hobby and HO model train supplies, I have purchased many, many items from Asia and China suppliers, and have never been disappointed, in terms of getting what I paid for as described.  It just takes 10-20 days for delivery.  The feedback should give an indication of the supplier reliability.